tools/perf/util/Build | 1 + tools/perf/util/dso.c | 2 + tools/perf/util/dso.h | 11 +++ tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++ tools/perf/util/libdw.h | 60 +++++++++++++++++ tools/perf/util/srcline.c | 5 ++ 6 files changed, 215 insertions(+) create mode 100644 tools/perf/util/libdw.c create mode 100644 tools/perf/util/libdw.h
Add an implementation of addr2line that uses libdw. Other addr2line
implementations or, in the case of forking addr2line, slow. Add an
implementation that caches the libdw information in the dso and uses
it to find the file and line number information.
Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/Build | 1 +
tools/perf/util/dso.c | 2 +
tools/perf/util/dso.h | 11 +++
tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
tools/perf/util/libdw.h | 60 +++++++++++++++++
tools/perf/util/srcline.c | 5 ++
6 files changed, 215 insertions(+)
create mode 100644 tools/perf/util/libdw.c
create mode 100644 tools/perf/util/libdw.h
diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 1c2a43e1dc68..2bed6274e248 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
perf-util-$(CONFIG_LIBDW) += debuginfo.o
perf-util-$(CONFIG_LIBDW) += annotate-data.o
+perf-util-$(CONFIG_LIBDW) += libdw.o
perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 344e689567ee..06980844c014 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -32,6 +32,7 @@
#include "string2.h"
#include "vdso.h"
#include "annotate-data.h"
+#include "libdw.h"
static const char * const debuglink_paths[] = {
"%.0s%s",
@@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
dso_cache__free(dso);
dso__free_a2l(dso);
+ dso__free_a2l_libdw(dso);
dso__free_symsrc_filename(dso);
nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
mutex_destroy(dso__lock(dso));
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index f8ccb9816b89..4aee23775054 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
const char *short_name;
const char *long_name;
void *a2l;
+ void *a2l_libdw;
char *symsrc_filename;
#if defined(__powerpc__)
void *dwfl; /* DWARF debug info */
@@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
RC_CHK_ACCESS(dso)->a2l = val;
}
+static inline void *dso__a2l_libdw(const struct dso *dso)
+{
+ return RC_CHK_ACCESS(dso)->a2l_libdw;
+}
+
+static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
+{
+ RC_CHK_ACCESS(dso)->a2l_libdw = val;
+}
+
static inline unsigned int dso__a2l_fails(const struct dso *dso)
{
return RC_CHK_ACCESS(dso)->a2l_fails;
diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
new file mode 100644
index 000000000000..c4331fa8e1a3
--- /dev/null
+++ b/tools/perf/util/libdw.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "dso.h"
+#include "libdw.h"
+#include "srcline.h"
+#include "symbol.h"
+#include "dwarf-aux.h"
+#include <fcntl.h>
+#include <unistd.h>
+#include <elfutils/libdwfl.h>
+
+void dso__free_a2l_libdw(struct dso *dso)
+{
+ Dwfl *dwfl = dso__a2l_libdw(dso);
+
+ if (dwfl) {
+ dwfl_end(dwfl);
+ dso__set_a2l_libdw(dso, NULL);
+ }
+}
+
+int libdw__addr2line(const char *dso_name, u64 addr,
+ char **file, unsigned int *line_nr,
+ struct dso *dso, bool unwind_inlines,
+ struct inline_node *node, struct symbol *sym)
+{
+ static const Dwfl_Callbacks offline_callbacks = {
+ .find_debuginfo = dwfl_standard_find_debuginfo,
+ .section_address = dwfl_offline_section_address,
+ .find_elf = dwfl_build_id_find_elf,
+ };
+ Dwfl *dwfl = dso__a2l_libdw(dso);
+ Dwfl_Module *mod;
+ Dwfl_Line *dwline;
+ Dwarf_Addr bias;
+ const char *src;
+ int lineno;
+
+ if (!dwfl) {
+ /*
+ * Initialize Dwfl session.
+ * We need to open the DSO file to report it to libdw.
+ */
+ int fd;
+
+ fd = open(dso_name, O_RDONLY);
+ if (fd < 0)
+ return 0;
+
+ dwfl = dwfl_begin(&offline_callbacks);
+ if (!dwfl) {
+ close(fd);
+ return 0;
+ }
+
+ /*
+ * If the report is successful, the file descriptor fd is consumed
+ * and closed by the Dwfl. If not, it is not closed.
+ */
+ mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
+ if (!mod) {
+ dwfl_end(dwfl);
+ close(fd);
+ return 0;
+ }
+
+ dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
+ dso__set_a2l_libdw(dso, dwfl);
+ } else {
+ /* Dwfl session already initialized, get module for address. */
+ mod = dwfl_addrmodule(dwfl, addr);
+ }
+
+ if (!mod)
+ return 0;
+
+ /* Find source line information for the address. */
+ dwline = dwfl_module_getsrc(mod, addr);
+ if (!dwline)
+ return 0;
+
+ /* Get line information. */
+ src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
+
+ if (file)
+ *file = src ? strdup(src) : NULL;
+ if (line_nr)
+ *line_nr = lineno;
+
+ /* Optionally unwind inline function call chain. */
+ if (unwind_inlines && node && src) {
+ Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
+ Dwarf_Die *scopes = NULL;
+ int nscopes;
+
+ if (!cudie)
+ return 1;
+
+ nscopes = die_get_scopes(cudie, addr, &scopes);
+ if (nscopes > 0) {
+ int i;
+ const char *call_file = src;
+ unsigned int call_line = lineno;
+
+ for (i = 0; i < nscopes; i++) {
+ Dwarf_Die *die = &scopes[i];
+ struct symbol *inline_sym;
+ char *srcline = NULL;
+ int tag = dwarf_tag(die);
+
+ /* We are interested in inlined subroutines. */
+ if (tag != DW_TAG_inlined_subroutine &&
+ tag != DW_TAG_subprogram)
+ continue;
+
+ inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
+
+ if (call_file)
+ srcline = srcline_from_fileline(call_file, call_line);
+
+ inline_list__append(inline_sym, srcline, node);
+
+ /* Update call site for next level. */
+ if (tag == DW_TAG_inlined_subroutine) {
+ call_file = die_get_call_file(die);
+ call_line = die_get_call_lineno(die);
+ } else {
+ /* Reached the root subprogram. */
+ break;
+ }
+ }
+ free(scopes);
+ }
+ }
+
+ return 1;
+}
diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
new file mode 100644
index 000000000000..0f8d7b4a11a5
--- /dev/null
+++ b/tools/perf/util/libdw.h
@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef PERF_LIBDW_H
+#define PERF_LIBDW_H
+
+#include <linux/types.h>
+
+struct dso;
+struct inline_node;
+struct symbol;
+
+#ifdef HAVE_LIBDW_SUPPORT
+/*
+ * libdw__addr2line - Convert address to source location using libdw
+ * @dso_name: Name of the DSO
+ * @addr: Address to resolve
+ * @file: Pointer to return filename (caller must free)
+ * @line_nr: Pointer to return line number
+ * @dso: The dso struct
+ * @unwind_inlines: Whether to unwind inline function calls
+ * @node: Inline node list to append to
+ * @sym: The symbol associated with the address
+ *
+ * This function initializes a Dwfl context for the DSO if not already present,
+ * finds the source line information for the given address, and optionally
+ * resolves inline function call chains.
+ *
+ * Returns 1 on success (found), 0 on failure (not found).
+ */
+int libdw__addr2line(const char *dso_name, u64 addr, char **file,
+ unsigned int *line_nr, struct dso *dso,
+ bool unwind_inlines, struct inline_node *node,
+ struct symbol *sym);
+
+/*
+ * dso__free_a2l_libdw - Free libdw resources associated with the DSO
+ * @dso: The dso to free resources for
+ *
+ * This function cleans up the Dwfl context used for addr2line lookups.
+ */
+void dso__free_a2l_libdw(struct dso *dso);
+
+#else /* HAVE_LIBDW_SUPPORT */
+
+static inline int libdw__addr2line(const char *dso_name __maybe_unused,
+ u64 addr __maybe_unused, char **file __maybe_unused,
+ unsigned int *line_nr __maybe_unused,
+ struct dso *dso __maybe_unused,
+ bool unwind_inlines __maybe_unused,
+ struct inline_node *node __maybe_unused,
+ struct symbol *sym __maybe_unused)
+{
+ return 0;
+}
+
+static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
+{
+}
+#endif /* HAVE_LIBDW_SUPPORT */
+
+#endif /* PERF_LIBDW_H */
diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
index 27c0966611ab..4b456c4d4138 100644
--- a/tools/perf/util/srcline.c
+++ b/tools/perf/util/srcline.c
@@ -6,6 +6,7 @@
#include "libbfd.h"
#include "llvm.h"
#include "symbol.h"
+#include "libdw.h"
#include <inttypes.h>
#include <string.h>
@@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
{
int ret;
+ ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
+ if (ret > 0)
+ return ret;
+
ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
if (ret > 0)
return ret;
--
2.52.0.rc2.455.g230fcf2819-googOn Sat, Nov 22, 2025 at 01:39:34AM -0800, Ian Rogers wrote:
> Add an implementation of addr2line that uses libdw. Other addr2line
> implementations or, in the case of forking addr2line, slow. Add an
> implementation that caches the libdw information in the dso and uses
> it to find the file and line number information.
My concern is the limit in the open file descriptors in case the data
touched a lot of different libraries. The DSO code has some logic to
deal with it but I'm not sure if we can share that since libdw seems to
want to own the FD.
Also, have you checked if this generates the exactly same output with
other implementations?
Thanks,
Namhyung
>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/util/Build | 1 +
> tools/perf/util/dso.c | 2 +
> tools/perf/util/dso.h | 11 +++
> tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
> tools/perf/util/libdw.h | 60 +++++++++++++++++
> tools/perf/util/srcline.c | 5 ++
> 6 files changed, 215 insertions(+)
> create mode 100644 tools/perf/util/libdw.c
> create mode 100644 tools/perf/util/libdw.h
>
> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> index 1c2a43e1dc68..2bed6274e248 100644
> --- a/tools/perf/util/Build
> +++ b/tools/perf/util/Build
> @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
> perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
> perf-util-$(CONFIG_LIBDW) += debuginfo.o
> perf-util-$(CONFIG_LIBDW) += annotate-data.o
> +perf-util-$(CONFIG_LIBDW) += libdw.o
>
> perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
> perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index 344e689567ee..06980844c014 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -32,6 +32,7 @@
> #include "string2.h"
> #include "vdso.h"
> #include "annotate-data.h"
> +#include "libdw.h"
>
> static const char * const debuglink_paths[] = {
> "%.0s%s",
> @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
> auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
> dso_cache__free(dso);
> dso__free_a2l(dso);
> + dso__free_a2l_libdw(dso);
> dso__free_symsrc_filename(dso);
> nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
> mutex_destroy(dso__lock(dso));
> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> index f8ccb9816b89..4aee23775054 100644
> --- a/tools/perf/util/dso.h
> +++ b/tools/perf/util/dso.h
> @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
> const char *short_name;
> const char *long_name;
> void *a2l;
> + void *a2l_libdw;
> char *symsrc_filename;
> #if defined(__powerpc__)
> void *dwfl; /* DWARF debug info */
> @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
> RC_CHK_ACCESS(dso)->a2l = val;
> }
>
> +static inline void *dso__a2l_libdw(const struct dso *dso)
> +{
> + return RC_CHK_ACCESS(dso)->a2l_libdw;
> +}
> +
> +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
> +{
> + RC_CHK_ACCESS(dso)->a2l_libdw = val;
> +}
> +
> static inline unsigned int dso__a2l_fails(const struct dso *dso)
> {
> return RC_CHK_ACCESS(dso)->a2l_fails;
> diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
> new file mode 100644
> index 000000000000..c4331fa8e1a3
> --- /dev/null
> +++ b/tools/perf/util/libdw.c
> @@ -0,0 +1,136 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "dso.h"
> +#include "libdw.h"
> +#include "srcline.h"
> +#include "symbol.h"
> +#include "dwarf-aux.h"
> +#include <fcntl.h>
> +#include <unistd.h>
> +#include <elfutils/libdwfl.h>
> +
> +void dso__free_a2l_libdw(struct dso *dso)
> +{
> + Dwfl *dwfl = dso__a2l_libdw(dso);
> +
> + if (dwfl) {
> + dwfl_end(dwfl);
> + dso__set_a2l_libdw(dso, NULL);
> + }
> +}
> +
> +int libdw__addr2line(const char *dso_name, u64 addr,
> + char **file, unsigned int *line_nr,
> + struct dso *dso, bool unwind_inlines,
> + struct inline_node *node, struct symbol *sym)
> +{
> + static const Dwfl_Callbacks offline_callbacks = {
> + .find_debuginfo = dwfl_standard_find_debuginfo,
> + .section_address = dwfl_offline_section_address,
> + .find_elf = dwfl_build_id_find_elf,
> + };
> + Dwfl *dwfl = dso__a2l_libdw(dso);
> + Dwfl_Module *mod;
> + Dwfl_Line *dwline;
> + Dwarf_Addr bias;
> + const char *src;
> + int lineno;
> +
> + if (!dwfl) {
> + /*
> + * Initialize Dwfl session.
> + * We need to open the DSO file to report it to libdw.
> + */
> + int fd;
> +
> + fd = open(dso_name, O_RDONLY);
> + if (fd < 0)
> + return 0;
> +
> + dwfl = dwfl_begin(&offline_callbacks);
> + if (!dwfl) {
> + close(fd);
> + return 0;
> + }
> +
> + /*
> + * If the report is successful, the file descriptor fd is consumed
> + * and closed by the Dwfl. If not, it is not closed.
> + */
> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> + if (!mod) {
> + dwfl_end(dwfl);
> + close(fd);
> + return 0;
> + }
> +
> + dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
> + dso__set_a2l_libdw(dso, dwfl);
> + } else {
> + /* Dwfl session already initialized, get module for address. */
> + mod = dwfl_addrmodule(dwfl, addr);
> + }
> +
> + if (!mod)
> + return 0;
> +
> + /* Find source line information for the address. */
> + dwline = dwfl_module_getsrc(mod, addr);
> + if (!dwline)
> + return 0;
> +
> + /* Get line information. */
> + src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
> +
> + if (file)
> + *file = src ? strdup(src) : NULL;
> + if (line_nr)
> + *line_nr = lineno;
> +
> + /* Optionally unwind inline function call chain. */
> + if (unwind_inlines && node && src) {
> + Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
> + Dwarf_Die *scopes = NULL;
> + int nscopes;
> +
> + if (!cudie)
> + return 1;
> +
> + nscopes = die_get_scopes(cudie, addr, &scopes);
> + if (nscopes > 0) {
> + int i;
> + const char *call_file = src;
> + unsigned int call_line = lineno;
> +
> + for (i = 0; i < nscopes; i++) {
> + Dwarf_Die *die = &scopes[i];
> + struct symbol *inline_sym;
> + char *srcline = NULL;
> + int tag = dwarf_tag(die);
> +
> + /* We are interested in inlined subroutines. */
> + if (tag != DW_TAG_inlined_subroutine &&
> + tag != DW_TAG_subprogram)
> + continue;
> +
> + inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
> +
> + if (call_file)
> + srcline = srcline_from_fileline(call_file, call_line);
> +
> + inline_list__append(inline_sym, srcline, node);
> +
> + /* Update call site for next level. */
> + if (tag == DW_TAG_inlined_subroutine) {
> + call_file = die_get_call_file(die);
> + call_line = die_get_call_lineno(die);
> + } else {
> + /* Reached the root subprogram. */
> + break;
> + }
> + }
> + free(scopes);
> + }
> + }
> +
> + return 1;
> +}
> diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
> new file mode 100644
> index 000000000000..0f8d7b4a11a5
> --- /dev/null
> +++ b/tools/perf/util/libdw.h
> @@ -0,0 +1,60 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef PERF_LIBDW_H
> +#define PERF_LIBDW_H
> +
> +#include <linux/types.h>
> +
> +struct dso;
> +struct inline_node;
> +struct symbol;
> +
> +#ifdef HAVE_LIBDW_SUPPORT
> +/*
> + * libdw__addr2line - Convert address to source location using libdw
> + * @dso_name: Name of the DSO
> + * @addr: Address to resolve
> + * @file: Pointer to return filename (caller must free)
> + * @line_nr: Pointer to return line number
> + * @dso: The dso struct
> + * @unwind_inlines: Whether to unwind inline function calls
> + * @node: Inline node list to append to
> + * @sym: The symbol associated with the address
> + *
> + * This function initializes a Dwfl context for the DSO if not already present,
> + * finds the source line information for the given address, and optionally
> + * resolves inline function call chains.
> + *
> + * Returns 1 on success (found), 0 on failure (not found).
> + */
> +int libdw__addr2line(const char *dso_name, u64 addr, char **file,
> + unsigned int *line_nr, struct dso *dso,
> + bool unwind_inlines, struct inline_node *node,
> + struct symbol *sym);
> +
> +/*
> + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
> + * @dso: The dso to free resources for
> + *
> + * This function cleans up the Dwfl context used for addr2line lookups.
> + */
> +void dso__free_a2l_libdw(struct dso *dso);
> +
> +#else /* HAVE_LIBDW_SUPPORT */
> +
> +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
> + u64 addr __maybe_unused, char **file __maybe_unused,
> + unsigned int *line_nr __maybe_unused,
> + struct dso *dso __maybe_unused,
> + bool unwind_inlines __maybe_unused,
> + struct inline_node *node __maybe_unused,
> + struct symbol *sym __maybe_unused)
> +{
> + return 0;
> +}
> +
> +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
> +{
> +}
> +#endif /* HAVE_LIBDW_SUPPORT */
> +
> +#endif /* PERF_LIBDW_H */
> diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
> index 27c0966611ab..4b456c4d4138 100644
> --- a/tools/perf/util/srcline.c
> +++ b/tools/perf/util/srcline.c
> @@ -6,6 +6,7 @@
> #include "libbfd.h"
> #include "llvm.h"
> #include "symbol.h"
> +#include "libdw.h"
>
> #include <inttypes.h>
> #include <string.h>
> @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
> {
> int ret;
>
> + ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> + if (ret > 0)
> + return ret;
> +
> ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> if (ret > 0)
> return ret;
> --
> 2.52.0.rc2.455.g230fcf2819-goog
>
On Wed, Nov 26, 2025 at 10:27 AM Namhyung Kim <namhyung@kernel.org> wrote:
>
> On Sat, Nov 22, 2025 at 01:39:34AM -0800, Ian Rogers wrote:
> > Add an implementation of addr2line that uses libdw. Other addr2line
> > implementations or, in the case of forking addr2line, slow. Add an
> > implementation that caches the libdw information in the dso and uses
> > it to find the file and line number information.
Thanks James and Namhyung for the reviews! I agree with James' comment
about a typo in the commit message.
> My concern is the limit in the open file descriptors in case the data
> touched a lot of different libraries. The DSO code has some logic to
> deal with it but I'm not sure if we can share that since libdw seems to
> want to own the FD.
The code opens the FD:
+ fd = open(dso_name, O_RDONLY);
+ if (fd < 0)
+ return 0;
+
+ dwfl = dwfl_begin(&offline_callbacks);
+ if (!dwfl) {
+ close(fd);
+ return 0;
+ }
It then uses the FD and closes it (the close is hidden in libdw itself):
+ /*
+ * If the report is successful, the file descriptor fd
is consumed
+ * and closed by the Dwfl. If not, it is not closed.
+ */
+ mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
So it is possible we exhaust all the file descriptors if there are
multiple concurrent calls to libdw__addr2line and every dso has
missing libdw dwfl data... but because the open/close are close
together and that 1 FD is say small to the FDs needed for the
cmd__addr2line, I don't think it is a problem we need to specifically
handle. Were the FD kept open until the dso was deleted, I'd agree
with you.
> Also, have you checked if this generates the exactly same output with
> other implementations?
So the code passes `perf test` and I was checking functionality with
perf annotate, top, etc. What I saw looked good, but it may not have
been exhaustive. I didn't specifically create a test that compares the
output of the different addr2line implementations. Such a test would
be possible, it's not something we've done elsewhere.
Thanks,
Ian
> Thanks,
> Namhyung
>
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> > tools/perf/util/Build | 1 +
> > tools/perf/util/dso.c | 2 +
> > tools/perf/util/dso.h | 11 +++
> > tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
> > tools/perf/util/libdw.h | 60 +++++++++++++++++
> > tools/perf/util/srcline.c | 5 ++
> > 6 files changed, 215 insertions(+)
> > create mode 100644 tools/perf/util/libdw.c
> > create mode 100644 tools/perf/util/libdw.h
> >
> > diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> > index 1c2a43e1dc68..2bed6274e248 100644
> > --- a/tools/perf/util/Build
> > +++ b/tools/perf/util/Build
> > @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
> > perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
> > perf-util-$(CONFIG_LIBDW) += debuginfo.o
> > perf-util-$(CONFIG_LIBDW) += annotate-data.o
> > +perf-util-$(CONFIG_LIBDW) += libdw.o
> >
> > perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
> > perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
> > diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> > index 344e689567ee..06980844c014 100644
> > --- a/tools/perf/util/dso.c
> > +++ b/tools/perf/util/dso.c
> > @@ -32,6 +32,7 @@
> > #include "string2.h"
> > #include "vdso.h"
> > #include "annotate-data.h"
> > +#include "libdw.h"
> >
> > static const char * const debuglink_paths[] = {
> > "%.0s%s",
> > @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
> > auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
> > dso_cache__free(dso);
> > dso__free_a2l(dso);
> > + dso__free_a2l_libdw(dso);
> > dso__free_symsrc_filename(dso);
> > nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
> > mutex_destroy(dso__lock(dso));
> > diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> > index f8ccb9816b89..4aee23775054 100644
> > --- a/tools/perf/util/dso.h
> > +++ b/tools/perf/util/dso.h
> > @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
> > const char *short_name;
> > const char *long_name;
> > void *a2l;
> > + void *a2l_libdw;
> > char *symsrc_filename;
> > #if defined(__powerpc__)
> > void *dwfl; /* DWARF debug info */
> > @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
> > RC_CHK_ACCESS(dso)->a2l = val;
> > }
> >
> > +static inline void *dso__a2l_libdw(const struct dso *dso)
> > +{
> > + return RC_CHK_ACCESS(dso)->a2l_libdw;
> > +}
> > +
> > +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
> > +{
> > + RC_CHK_ACCESS(dso)->a2l_libdw = val;
> > +}
> > +
> > static inline unsigned int dso__a2l_fails(const struct dso *dso)
> > {
> > return RC_CHK_ACCESS(dso)->a2l_fails;
> > diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
> > new file mode 100644
> > index 000000000000..c4331fa8e1a3
> > --- /dev/null
> > +++ b/tools/perf/util/libdw.c
> > @@ -0,0 +1,136 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include "dso.h"
> > +#include "libdw.h"
> > +#include "srcline.h"
> > +#include "symbol.h"
> > +#include "dwarf-aux.h"
> > +#include <fcntl.h>
> > +#include <unistd.h>
> > +#include <elfutils/libdwfl.h>
> > +
> > +void dso__free_a2l_libdw(struct dso *dso)
> > +{
> > + Dwfl *dwfl = dso__a2l_libdw(dso);
> > +
> > + if (dwfl) {
> > + dwfl_end(dwfl);
> > + dso__set_a2l_libdw(dso, NULL);
> > + }
> > +}
> > +
> > +int libdw__addr2line(const char *dso_name, u64 addr,
> > + char **file, unsigned int *line_nr,
> > + struct dso *dso, bool unwind_inlines,
> > + struct inline_node *node, struct symbol *sym)
> > +{
> > + static const Dwfl_Callbacks offline_callbacks = {
> > + .find_debuginfo = dwfl_standard_find_debuginfo,
> > + .section_address = dwfl_offline_section_address,
> > + .find_elf = dwfl_build_id_find_elf,
> > + };
> > + Dwfl *dwfl = dso__a2l_libdw(dso);
> > + Dwfl_Module *mod;
> > + Dwfl_Line *dwline;
> > + Dwarf_Addr bias;
> > + const char *src;
> > + int lineno;
> > +
> > + if (!dwfl) {
> > + /*
> > + * Initialize Dwfl session.
> > + * We need to open the DSO file to report it to libdw.
> > + */
> > + int fd;
> > +
> > + fd = open(dso_name, O_RDONLY);
> > + if (fd < 0)
> > + return 0;
> > +
> > + dwfl = dwfl_begin(&offline_callbacks);
> > + if (!dwfl) {
> > + close(fd);
> > + return 0;
> > + }
> > +
> > + /*
> > + * If the report is successful, the file descriptor fd is consumed
> > + * and closed by the Dwfl. If not, it is not closed.
> > + */
> > + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> > + if (!mod) {
> > + dwfl_end(dwfl);
> > + close(fd);
> > + return 0;
> > + }
> > +
> > + dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
> > + dso__set_a2l_libdw(dso, dwfl);
> > + } else {
> > + /* Dwfl session already initialized, get module for address. */
> > + mod = dwfl_addrmodule(dwfl, addr);
> > + }
> > +
> > + if (!mod)
> > + return 0;
> > +
> > + /* Find source line information for the address. */
> > + dwline = dwfl_module_getsrc(mod, addr);
> > + if (!dwline)
> > + return 0;
> > +
> > + /* Get line information. */
> > + src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
> > +
> > + if (file)
> > + *file = src ? strdup(src) : NULL;
> > + if (line_nr)
> > + *line_nr = lineno;
> > +
> > + /* Optionally unwind inline function call chain. */
> > + if (unwind_inlines && node && src) {
> > + Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
> > + Dwarf_Die *scopes = NULL;
> > + int nscopes;
> > +
> > + if (!cudie)
> > + return 1;
> > +
> > + nscopes = die_get_scopes(cudie, addr, &scopes);
> > + if (nscopes > 0) {
> > + int i;
> > + const char *call_file = src;
> > + unsigned int call_line = lineno;
> > +
> > + for (i = 0; i < nscopes; i++) {
> > + Dwarf_Die *die = &scopes[i];
> > + struct symbol *inline_sym;
> > + char *srcline = NULL;
> > + int tag = dwarf_tag(die);
> > +
> > + /* We are interested in inlined subroutines. */
> > + if (tag != DW_TAG_inlined_subroutine &&
> > + tag != DW_TAG_subprogram)
> > + continue;
> > +
> > + inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
> > +
> > + if (call_file)
> > + srcline = srcline_from_fileline(call_file, call_line);
> > +
> > + inline_list__append(inline_sym, srcline, node);
> > +
> > + /* Update call site for next level. */
> > + if (tag == DW_TAG_inlined_subroutine) {
> > + call_file = die_get_call_file(die);
> > + call_line = die_get_call_lineno(die);
> > + } else {
> > + /* Reached the root subprogram. */
> > + break;
> > + }
> > + }
> > + free(scopes);
> > + }
> > + }
> > +
> > + return 1;
> > +}
> > diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
> > new file mode 100644
> > index 000000000000..0f8d7b4a11a5
> > --- /dev/null
> > +++ b/tools/perf/util/libdw.h
> > @@ -0,0 +1,60 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef PERF_LIBDW_H
> > +#define PERF_LIBDW_H
> > +
> > +#include <linux/types.h>
> > +
> > +struct dso;
> > +struct inline_node;
> > +struct symbol;
> > +
> > +#ifdef HAVE_LIBDW_SUPPORT
> > +/*
> > + * libdw__addr2line - Convert address to source location using libdw
> > + * @dso_name: Name of the DSO
> > + * @addr: Address to resolve
> > + * @file: Pointer to return filename (caller must free)
> > + * @line_nr: Pointer to return line number
> > + * @dso: The dso struct
> > + * @unwind_inlines: Whether to unwind inline function calls
> > + * @node: Inline node list to append to
> > + * @sym: The symbol associated with the address
> > + *
> > + * This function initializes a Dwfl context for the DSO if not already present,
> > + * finds the source line information for the given address, and optionally
> > + * resolves inline function call chains.
> > + *
> > + * Returns 1 on success (found), 0 on failure (not found).
> > + */
> > +int libdw__addr2line(const char *dso_name, u64 addr, char **file,
> > + unsigned int *line_nr, struct dso *dso,
> > + bool unwind_inlines, struct inline_node *node,
> > + struct symbol *sym);
> > +
> > +/*
> > + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
> > + * @dso: The dso to free resources for
> > + *
> > + * This function cleans up the Dwfl context used for addr2line lookups.
> > + */
> > +void dso__free_a2l_libdw(struct dso *dso);
> > +
> > +#else /* HAVE_LIBDW_SUPPORT */
> > +
> > +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
> > + u64 addr __maybe_unused, char **file __maybe_unused,
> > + unsigned int *line_nr __maybe_unused,
> > + struct dso *dso __maybe_unused,
> > + bool unwind_inlines __maybe_unused,
> > + struct inline_node *node __maybe_unused,
> > + struct symbol *sym __maybe_unused)
> > +{
> > + return 0;
> > +}
> > +
> > +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
> > +{
> > +}
> > +#endif /* HAVE_LIBDW_SUPPORT */
> > +
> > +#endif /* PERF_LIBDW_H */
> > diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
> > index 27c0966611ab..4b456c4d4138 100644
> > --- a/tools/perf/util/srcline.c
> > +++ b/tools/perf/util/srcline.c
> > @@ -6,6 +6,7 @@
> > #include "libbfd.h"
> > #include "llvm.h"
> > #include "symbol.h"
> > +#include "libdw.h"
> >
> > #include <inttypes.h>
> > #include <string.h>
> > @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
> > {
> > int ret;
> >
> > + ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> > + if (ret > 0)
> > + return ret;
> > +
> > ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> > if (ret > 0)
> > return ret;
> > --
> > 2.52.0.rc2.455.g230fcf2819-goog
> >
On Thu, Nov 27, 2025 at 03:43:34AM -0800, Ian Rogers wrote:
> On Wed, Nov 26, 2025 at 10:27 AM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > On Sat, Nov 22, 2025 at 01:39:34AM -0800, Ian Rogers wrote:
> > > Add an implementation of addr2line that uses libdw. Other addr2line
> > > implementations or, in the case of forking addr2line, slow. Add an
> > > implementation that caches the libdw information in the dso and uses
> > > it to find the file and line number information.
>
> Thanks James and Namhyung for the reviews! I agree with James' comment
> about a typo in the commit message.
>
> > My concern is the limit in the open file descriptors in case the data
> > touched a lot of different libraries. The DSO code has some logic to
> > deal with it but I'm not sure if we can share that since libdw seems to
> > want to own the FD.
>
> The code opens the FD:
>
> + fd = open(dso_name, O_RDONLY);
> + if (fd < 0)
> + return 0;
> +
> + dwfl = dwfl_begin(&offline_callbacks);
> + if (!dwfl) {
> + close(fd);
> + return 0;
> + }
>
> It then uses the FD and closes it (the close is hidden in libdw itself):
>
> + /*
> + * If the report is successful, the file descriptor fd
> is consumed
> + * and closed by the Dwfl. If not, it is not closed.
> + */
> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
>
> So it is possible we exhaust all the file descriptors if there are
> multiple concurrent calls to libdw__addr2line and every dso has
> missing libdw dwfl data... but because the open/close are close
> together and that 1 FD is say small to the FDs needed for the
> cmd__addr2line, I don't think it is a problem we need to specifically
> handle. Were the FD kept open until the dso was deleted, I'd agree
> with you.
Oh, I thought libdwfl keeps the FD open until you call dwfl_end().
Are you sure the dwfl function would close the FD? I've quickly checked
the code, but it doesn't seem to close if you pass an FD manually.
Thanks,
Namhyung
>
> > Also, have you checked if this generates the exactly same output with
> > other implementations?
>
> So the code passes `perf test` and I was checking functionality with
> perf annotate, top, etc. What I saw looked good, but it may not have
> been exhaustive. I didn't specifically create a test that compares the
> output of the different addr2line implementations. Such a test would
> be possible, it's not something we've done elsewhere.
>
> Thanks,
> Ian
>
> > Thanks,
> > Namhyung
> >
> > >
> > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > ---
> > > tools/perf/util/Build | 1 +
> > > tools/perf/util/dso.c | 2 +
> > > tools/perf/util/dso.h | 11 +++
> > > tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
> > > tools/perf/util/libdw.h | 60 +++++++++++++++++
> > > tools/perf/util/srcline.c | 5 ++
> > > 6 files changed, 215 insertions(+)
> > > create mode 100644 tools/perf/util/libdw.c
> > > create mode 100644 tools/perf/util/libdw.h
> > >
> > > diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> > > index 1c2a43e1dc68..2bed6274e248 100644
> > > --- a/tools/perf/util/Build
> > > +++ b/tools/perf/util/Build
> > > @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
> > > perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
> > > perf-util-$(CONFIG_LIBDW) += debuginfo.o
> > > perf-util-$(CONFIG_LIBDW) += annotate-data.o
> > > +perf-util-$(CONFIG_LIBDW) += libdw.o
> > >
> > > perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
> > > perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
> > > diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> > > index 344e689567ee..06980844c014 100644
> > > --- a/tools/perf/util/dso.c
> > > +++ b/tools/perf/util/dso.c
> > > @@ -32,6 +32,7 @@
> > > #include "string2.h"
> > > #include "vdso.h"
> > > #include "annotate-data.h"
> > > +#include "libdw.h"
> > >
> > > static const char * const debuglink_paths[] = {
> > > "%.0s%s",
> > > @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
> > > auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
> > > dso_cache__free(dso);
> > > dso__free_a2l(dso);
> > > + dso__free_a2l_libdw(dso);
> > > dso__free_symsrc_filename(dso);
> > > nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
> > > mutex_destroy(dso__lock(dso));
> > > diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> > > index f8ccb9816b89..4aee23775054 100644
> > > --- a/tools/perf/util/dso.h
> > > +++ b/tools/perf/util/dso.h
> > > @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
> > > const char *short_name;
> > > const char *long_name;
> > > void *a2l;
> > > + void *a2l_libdw;
> > > char *symsrc_filename;
> > > #if defined(__powerpc__)
> > > void *dwfl; /* DWARF debug info */
> > > @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
> > > RC_CHK_ACCESS(dso)->a2l = val;
> > > }
> > >
> > > +static inline void *dso__a2l_libdw(const struct dso *dso)
> > > +{
> > > + return RC_CHK_ACCESS(dso)->a2l_libdw;
> > > +}
> > > +
> > > +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
> > > +{
> > > + RC_CHK_ACCESS(dso)->a2l_libdw = val;
> > > +}
> > > +
> > > static inline unsigned int dso__a2l_fails(const struct dso *dso)
> > > {
> > > return RC_CHK_ACCESS(dso)->a2l_fails;
> > > diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
> > > new file mode 100644
> > > index 000000000000..c4331fa8e1a3
> > > --- /dev/null
> > > +++ b/tools/perf/util/libdw.c
> > > @@ -0,0 +1,136 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +#include "dso.h"
> > > +#include "libdw.h"
> > > +#include "srcline.h"
> > > +#include "symbol.h"
> > > +#include "dwarf-aux.h"
> > > +#include <fcntl.h>
> > > +#include <unistd.h>
> > > +#include <elfutils/libdwfl.h>
> > > +
> > > +void dso__free_a2l_libdw(struct dso *dso)
> > > +{
> > > + Dwfl *dwfl = dso__a2l_libdw(dso);
> > > +
> > > + if (dwfl) {
> > > + dwfl_end(dwfl);
> > > + dso__set_a2l_libdw(dso, NULL);
> > > + }
> > > +}
> > > +
> > > +int libdw__addr2line(const char *dso_name, u64 addr,
> > > + char **file, unsigned int *line_nr,
> > > + struct dso *dso, bool unwind_inlines,
> > > + struct inline_node *node, struct symbol *sym)
> > > +{
> > > + static const Dwfl_Callbacks offline_callbacks = {
> > > + .find_debuginfo = dwfl_standard_find_debuginfo,
> > > + .section_address = dwfl_offline_section_address,
> > > + .find_elf = dwfl_build_id_find_elf,
> > > + };
> > > + Dwfl *dwfl = dso__a2l_libdw(dso);
> > > + Dwfl_Module *mod;
> > > + Dwfl_Line *dwline;
> > > + Dwarf_Addr bias;
> > > + const char *src;
> > > + int lineno;
> > > +
> > > + if (!dwfl) {
> > > + /*
> > > + * Initialize Dwfl session.
> > > + * We need to open the DSO file to report it to libdw.
> > > + */
> > > + int fd;
> > > +
> > > + fd = open(dso_name, O_RDONLY);
> > > + if (fd < 0)
> > > + return 0;
> > > +
> > > + dwfl = dwfl_begin(&offline_callbacks);
> > > + if (!dwfl) {
> > > + close(fd);
> > > + return 0;
> > > + }
> > > +
> > > + /*
> > > + * If the report is successful, the file descriptor fd is consumed
> > > + * and closed by the Dwfl. If not, it is not closed.
> > > + */
> > > + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> > > + if (!mod) {
> > > + dwfl_end(dwfl);
> > > + close(fd);
> > > + return 0;
> > > + }
> > > +
> > > + dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
> > > + dso__set_a2l_libdw(dso, dwfl);
> > > + } else {
> > > + /* Dwfl session already initialized, get module for address. */
> > > + mod = dwfl_addrmodule(dwfl, addr);
> > > + }
> > > +
> > > + if (!mod)
> > > + return 0;
> > > +
> > > + /* Find source line information for the address. */
> > > + dwline = dwfl_module_getsrc(mod, addr);
> > > + if (!dwline)
> > > + return 0;
> > > +
> > > + /* Get line information. */
> > > + src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
> > > +
> > > + if (file)
> > > + *file = src ? strdup(src) : NULL;
> > > + if (line_nr)
> > > + *line_nr = lineno;
> > > +
> > > + /* Optionally unwind inline function call chain. */
> > > + if (unwind_inlines && node && src) {
> > > + Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
> > > + Dwarf_Die *scopes = NULL;
> > > + int nscopes;
> > > +
> > > + if (!cudie)
> > > + return 1;
> > > +
> > > + nscopes = die_get_scopes(cudie, addr, &scopes);
> > > + if (nscopes > 0) {
> > > + int i;
> > > + const char *call_file = src;
> > > + unsigned int call_line = lineno;
> > > +
> > > + for (i = 0; i < nscopes; i++) {
> > > + Dwarf_Die *die = &scopes[i];
> > > + struct symbol *inline_sym;
> > > + char *srcline = NULL;
> > > + int tag = dwarf_tag(die);
> > > +
> > > + /* We are interested in inlined subroutines. */
> > > + if (tag != DW_TAG_inlined_subroutine &&
> > > + tag != DW_TAG_subprogram)
> > > + continue;
> > > +
> > > + inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
> > > +
> > > + if (call_file)
> > > + srcline = srcline_from_fileline(call_file, call_line);
> > > +
> > > + inline_list__append(inline_sym, srcline, node);
> > > +
> > > + /* Update call site for next level. */
> > > + if (tag == DW_TAG_inlined_subroutine) {
> > > + call_file = die_get_call_file(die);
> > > + call_line = die_get_call_lineno(die);
> > > + } else {
> > > + /* Reached the root subprogram. */
> > > + break;
> > > + }
> > > + }
> > > + free(scopes);
> > > + }
> > > + }
> > > +
> > > + return 1;
> > > +}
> > > diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
> > > new file mode 100644
> > > index 000000000000..0f8d7b4a11a5
> > > --- /dev/null
> > > +++ b/tools/perf/util/libdw.h
> > > @@ -0,0 +1,60 @@
> > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > +#ifndef PERF_LIBDW_H
> > > +#define PERF_LIBDW_H
> > > +
> > > +#include <linux/types.h>
> > > +
> > > +struct dso;
> > > +struct inline_node;
> > > +struct symbol;
> > > +
> > > +#ifdef HAVE_LIBDW_SUPPORT
> > > +/*
> > > + * libdw__addr2line - Convert address to source location using libdw
> > > + * @dso_name: Name of the DSO
> > > + * @addr: Address to resolve
> > > + * @file: Pointer to return filename (caller must free)
> > > + * @line_nr: Pointer to return line number
> > > + * @dso: The dso struct
> > > + * @unwind_inlines: Whether to unwind inline function calls
> > > + * @node: Inline node list to append to
> > > + * @sym: The symbol associated with the address
> > > + *
> > > + * This function initializes a Dwfl context for the DSO if not already present,
> > > + * finds the source line information for the given address, and optionally
> > > + * resolves inline function call chains.
> > > + *
> > > + * Returns 1 on success (found), 0 on failure (not found).
> > > + */
> > > +int libdw__addr2line(const char *dso_name, u64 addr, char **file,
> > > + unsigned int *line_nr, struct dso *dso,
> > > + bool unwind_inlines, struct inline_node *node,
> > > + struct symbol *sym);
> > > +
> > > +/*
> > > + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
> > > + * @dso: The dso to free resources for
> > > + *
> > > + * This function cleans up the Dwfl context used for addr2line lookups.
> > > + */
> > > +void dso__free_a2l_libdw(struct dso *dso);
> > > +
> > > +#else /* HAVE_LIBDW_SUPPORT */
> > > +
> > > +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
> > > + u64 addr __maybe_unused, char **file __maybe_unused,
> > > + unsigned int *line_nr __maybe_unused,
> > > + struct dso *dso __maybe_unused,
> > > + bool unwind_inlines __maybe_unused,
> > > + struct inline_node *node __maybe_unused,
> > > + struct symbol *sym __maybe_unused)
> > > +{
> > > + return 0;
> > > +}
> > > +
> > > +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
> > > +{
> > > +}
> > > +#endif /* HAVE_LIBDW_SUPPORT */
> > > +
> > > +#endif /* PERF_LIBDW_H */
> > > diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
> > > index 27c0966611ab..4b456c4d4138 100644
> > > --- a/tools/perf/util/srcline.c
> > > +++ b/tools/perf/util/srcline.c
> > > @@ -6,6 +6,7 @@
> > > #include "libbfd.h"
> > > #include "llvm.h"
> > > #include "symbol.h"
> > > +#include "libdw.h"
> > >
> > > #include <inttypes.h>
> > > #include <string.h>
> > > @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
> > > {
> > > int ret;
> > >
> > > + ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> > > + if (ret > 0)
> > > + return ret;
> > > +
> > > ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> > > if (ret > 0)
> > > return ret;
> > > --
> > > 2.52.0.rc2.455.g230fcf2819-goog
> > >
On Thu, Nov 27, 2025 at 12:53 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> On Thu, Nov 27, 2025 at 03:43:34AM -0800, Ian Rogers wrote:
> > On Wed, Nov 26, 2025 at 10:27 AM Namhyung Kim <namhyung@kernel.org> wrote:
> > >
> > > On Sat, Nov 22, 2025 at 01:39:34AM -0800, Ian Rogers wrote:
> > > > Add an implementation of addr2line that uses libdw. Other addr2line
> > > > implementations or, in the case of forking addr2line, slow. Add an
> > > > implementation that caches the libdw information in the dso and uses
> > > > it to find the file and line number information.
> >
> > Thanks James and Namhyung for the reviews! I agree with James' comment
> > about a typo in the commit message.
> >
> > > My concern is the limit in the open file descriptors in case the data
> > > touched a lot of different libraries. The DSO code has some logic to
> > > deal with it but I'm not sure if we can share that since libdw seems to
> > > want to own the FD.
> >
> > The code opens the FD:
> >
> > + fd = open(dso_name, O_RDONLY);
> > + if (fd < 0)
> > + return 0;
> > +
> > + dwfl = dwfl_begin(&offline_callbacks);
> > + if (!dwfl) {
> > + close(fd);
> > + return 0;
> > + }
> >
> > It then uses the FD and closes it (the close is hidden in libdw itself):
> >
> > + /*
> > + * If the report is successful, the file descriptor fd
> > is consumed
> > + * and closed by the Dwfl. If not, it is not closed.
> > + */
> > + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> >
> > So it is possible we exhaust all the file descriptors if there are
> > multiple concurrent calls to libdw__addr2line and every dso has
> > missing libdw dwfl data... but because the open/close are close
> > together and that 1 FD is say small to the FDs needed for the
> > cmd__addr2line, I don't think it is a problem we need to specifically
> > handle. Were the FD kept open until the dso was deleted, I'd agree
> > with you.
>
> Oh, I thought libdwfl keeps the FD open until you call dwfl_end().
> Are you sure the dwfl function would close the FD? I've quickly checked
> the code, but it doesn't seem to close if you pass an FD manually.
So in the documentation there is:
https://sourceware.org/git/?p=elfutils.git;a=blob;f=libdwfl/libdwfl.h;h=90523283c9359b09a16709a8422917a44257932f;hb=HEAD#l155
```
/* ...On success, FD is consumed by the
library, ... */
extern Dwfl_Module *dwfl_report_elf (Dwfl *dwfl, const char *name,
const char *file_name, int fd,
GElf_Addr base, bool add_p_vaddr);
/* Similar, but report the module for offline use. ... */
extern Dwfl_Module *dwfl_report_offline (Dwfl *dwfl, const char *name,
const char *file_name, int fd);
```
Running with gdb I see:
```
$ perf record perf test -w noploop
Lowering default frequency rate from 4000 to 2500.
Please consider tweaking /proc/sys/kernel/perf_event_max_sample_rate.
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.611 MB perf.data (2534 samples) ]
$ gdb --args perf --no-pager annotate -l --stdio
...
Reading symbols from /tmp/perf/perf...
(gdb) b libdw__addr2line
Breakpoint 1 at 0x392b98: file util/libdw.c, line 25.
(gdb) r
Starting program: /tmp/perf/perf --no-pager annotate -l --stdio
...
Breakpoint 1, libdw__addr2line (dso_name=0x555557b41270
"/root/.debug/.build-id/4c/72a04e484e8636631219f4454cc64a674a5f57/elf",
addr=1903613,
file=0x7fffffffa830, line_nr=0x7fffffffa82c, dso=0x5555569eba20,
unwind_inlines=false, node=0x0, sym=0x0) at util/libdw.c:25
25 {
(gdb) n
31 Dwfl *dwfl = dso__a2l_libdw(dso);
(gdb)
38 if (!dwfl) {
(gdb)
45 fd = open(dso_name, O_RDONLY);
(gdb)
46 if (fd < 0)
(gdb) p fd
$1 = 5
(gdb) n
49 dwfl = dwfl_begin(&offline_callbacks);
(gdb) b close
Breakpoint 2 at 0x7fffedf09760: close. (15 locations)
(gdb) c
Continuing.
Breakpoint 2.1, __GI___close (fd=5) at ../sysdeps/unix/sysv/linux/close.c:27
warning: 27 ../sysdeps/unix/sysv/linux/close.c: No such file or directory
(gdb) bt
#0 __GI___close (fd=5) at ../sysdeps/unix/sysv/linux/close.c:27
#1 0x00007ffff7e0e122 in ?? () from /lib/x86_64-linux-gnu/libdw.so.1
#2 0x00007ffff7e0e6f7 in ?? () from /lib/x86_64-linux-gnu/libdw.so.1
#3 0x00005555558e6c3c in libdw__addr2line (dso_name=0x555557b41270
"/root/.debug/.build-id/4c/72a04e484e8636631219f4454cc64a674a5f57/elf",
addr=1903613, file=0x7fffffffa830, line_nr=0x7fffffffa82c,
dso=0x5555569eba20, unwind_inlines=false, node=0x0, sym=0x0) at
util/libdw.c:59
#4 0x000055555584c861 in addr2line (dso_name=0x555557b41270
"/root/.debug/.build-id/4c/72a04e484e8636631219f4454cc64a674a5f57/elf",
addr=1903613, file=0x7fffffffa830, line_nr=0x7fffffffa82c,
dso=0x5555569eba20, unwind_inlines=false, node=0x0, sym=0x0)
at util/srcline.c:124
#5 0x000055555584ca9c in __get_srcline (dso=0x5555569eba20,
addr=1903613, sym=0x0, show_sym=false, show_addr=true,
unwind_inlines=false,
ip=1903613) at util/srcline.c:181
#6 0x000055555584ce21 in get_srcline (dso=0x5555569eba20,
addr=1903613, sym=0x0, show_sym=false, show_addr=true, ip=1903613)
at util/srcline.c:259
#7 0x0000555555754a63 in annotation__calc_lines
(notes=0x5555586d02d0, ms=0x555558665600, root=0x7fffffffa9a0) at
util/annotate.c:1651
#8 0x0000555555754b20 in symbol__calc_lines (ms=0x555558665600,
root=0x7fffffffa9a0) at util/annotate.c:1663
#9 0x0000555555754f22 in hist_entry__tty_annotate (he=0x555558665560,
evsel=0x5555561dc6e0) at util/annotate.c:1728
#10 0x00005555555a829a in hist_entry__stdio_annotate
(he=0x555558665560, evsel=0x5555561dc6e0, ann=0x7fffffffcc90) at
builtin-annotate.c:332
#11 0x00005555555a8ed4 in hists__find_annotations
(hists=0x5555561dc998, evsel=0x5555561dc6e0, ann=0x7fffffffcc90) at
builtin-annotate.c:545
#12 0x00005555555a9404 in __cmd_annotate (ann=0x7fffffffcc90) at
builtin-annotate.c:655
#13 0x00005555555aa5c6 in cmd_annotate (argc=0, argv=0x7fffffffe318)
at builtin-annotate.c:949
#14 0x0000555555655e11 in run_builtin (p=0x555556128650
<commands+432>, argc=3, argv=0x7fffffffe318) at perf.c:349
#15 0x00005555556560a9 in handle_internal_command (argc=3,
argv=0x7fffffffe318) at perf.c:401
#16 0x0000555555656202 in run_argv (argcp=0x7fffffffe10c,
argv=0x7fffffffe100) at perf.c:445
#17 0x000055555565654b in main (argc=3, argv=0x7fffffffe318) at perf.c:553
(gdb) frame 3
#3 0x00005555558e6c3c in libdw__addr2line (dso_name=0x555557b41270
"/root/.debug/.build-id/4c/72a04e484e8636631219f4454cc64a674a5f57/elf",
addr=1903613, file=0x7fffffffa830, line_nr=0x7fffffffa82c,
dso=0x5555569eba20, unwind_inlines=false, node=0x0, sym=0x0) at
util/libdw.c:59
59 mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
```
So I think everything is working as explained. The open happens
returning fd 5, dwfl_report_offline is called and on success it closes
fd 5. Were the dwfl_report_offline to fail then the error path in
libdw__addr2line closes fd.
Looking at older versions of the code (10 years old) the header file
documentation is the same, so I'm not sure why you are seeing a
different behavior.
Thanks,
Ian
> Thanks,
> Namhyung
>
> >
> > > Also, have you checked if this generates the exactly same output with
> > > other implementations?
> >
> > So the code passes `perf test` and I was checking functionality with
> > perf annotate, top, etc. What I saw looked good, but it may not have
> > been exhaustive. I didn't specifically create a test that compares the
> > output of the different addr2line implementations. Such a test would
> > be possible, it's not something we've done elsewhere.
> >
> > Thanks,
> > Ian
> >
> > > Thanks,
> > > Namhyung
> > >
> > > >
> > > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > > ---
> > > > tools/perf/util/Build | 1 +
> > > > tools/perf/util/dso.c | 2 +
> > > > tools/perf/util/dso.h | 11 +++
> > > > tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
> > > > tools/perf/util/libdw.h | 60 +++++++++++++++++
> > > > tools/perf/util/srcline.c | 5 ++
> > > > 6 files changed, 215 insertions(+)
> > > > create mode 100644 tools/perf/util/libdw.c
> > > > create mode 100644 tools/perf/util/libdw.h
> > > >
> > > > diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> > > > index 1c2a43e1dc68..2bed6274e248 100644
> > > > --- a/tools/perf/util/Build
> > > > +++ b/tools/perf/util/Build
> > > > @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
> > > > perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
> > > > perf-util-$(CONFIG_LIBDW) += debuginfo.o
> > > > perf-util-$(CONFIG_LIBDW) += annotate-data.o
> > > > +perf-util-$(CONFIG_LIBDW) += libdw.o
> > > >
> > > > perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
> > > > perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
> > > > diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> > > > index 344e689567ee..06980844c014 100644
> > > > --- a/tools/perf/util/dso.c
> > > > +++ b/tools/perf/util/dso.c
> > > > @@ -32,6 +32,7 @@
> > > > #include "string2.h"
> > > > #include "vdso.h"
> > > > #include "annotate-data.h"
> > > > +#include "libdw.h"
> > > >
> > > > static const char * const debuglink_paths[] = {
> > > > "%.0s%s",
> > > > @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
> > > > auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
> > > > dso_cache__free(dso);
> > > > dso__free_a2l(dso);
> > > > + dso__free_a2l_libdw(dso);
> > > > dso__free_symsrc_filename(dso);
> > > > nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
> > > > mutex_destroy(dso__lock(dso));
> > > > diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> > > > index f8ccb9816b89..4aee23775054 100644
> > > > --- a/tools/perf/util/dso.h
> > > > +++ b/tools/perf/util/dso.h
> > > > @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
> > > > const char *short_name;
> > > > const char *long_name;
> > > > void *a2l;
> > > > + void *a2l_libdw;
> > > > char *symsrc_filename;
> > > > #if defined(__powerpc__)
> > > > void *dwfl; /* DWARF debug info */
> > > > @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
> > > > RC_CHK_ACCESS(dso)->a2l = val;
> > > > }
> > > >
> > > > +static inline void *dso__a2l_libdw(const struct dso *dso)
> > > > +{
> > > > + return RC_CHK_ACCESS(dso)->a2l_libdw;
> > > > +}
> > > > +
> > > > +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
> > > > +{
> > > > + RC_CHK_ACCESS(dso)->a2l_libdw = val;
> > > > +}
> > > > +
> > > > static inline unsigned int dso__a2l_fails(const struct dso *dso)
> > > > {
> > > > return RC_CHK_ACCESS(dso)->a2l_fails;
> > > > diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
> > > > new file mode 100644
> > > > index 000000000000..c4331fa8e1a3
> > > > --- /dev/null
> > > > +++ b/tools/perf/util/libdw.c
> > > > @@ -0,0 +1,136 @@
> > > > +// SPDX-License-Identifier: GPL-2.0
> > > > +#include "dso.h"
> > > > +#include "libdw.h"
> > > > +#include "srcline.h"
> > > > +#include "symbol.h"
> > > > +#include "dwarf-aux.h"
> > > > +#include <fcntl.h>
> > > > +#include <unistd.h>
> > > > +#include <elfutils/libdwfl.h>
> > > > +
> > > > +void dso__free_a2l_libdw(struct dso *dso)
> > > > +{
> > > > + Dwfl *dwfl = dso__a2l_libdw(dso);
> > > > +
> > > > + if (dwfl) {
> > > > + dwfl_end(dwfl);
> > > > + dso__set_a2l_libdw(dso, NULL);
> > > > + }
> > > > +}
> > > > +
> > > > +int libdw__addr2line(const char *dso_name, u64 addr,
> > > > + char **file, unsigned int *line_nr,
> > > > + struct dso *dso, bool unwind_inlines,
> > > > + struct inline_node *node, struct symbol *sym)
> > > > +{
> > > > + static const Dwfl_Callbacks offline_callbacks = {
> > > > + .find_debuginfo = dwfl_standard_find_debuginfo,
> > > > + .section_address = dwfl_offline_section_address,
> > > > + .find_elf = dwfl_build_id_find_elf,
> > > > + };
> > > > + Dwfl *dwfl = dso__a2l_libdw(dso);
> > > > + Dwfl_Module *mod;
> > > > + Dwfl_Line *dwline;
> > > > + Dwarf_Addr bias;
> > > > + const char *src;
> > > > + int lineno;
> > > > +
> > > > + if (!dwfl) {
> > > > + /*
> > > > + * Initialize Dwfl session.
> > > > + * We need to open the DSO file to report it to libdw.
> > > > + */
> > > > + int fd;
> > > > +
> > > > + fd = open(dso_name, O_RDONLY);
> > > > + if (fd < 0)
> > > > + return 0;
> > > > +
> > > > + dwfl = dwfl_begin(&offline_callbacks);
> > > > + if (!dwfl) {
> > > > + close(fd);
> > > > + return 0;
> > > > + }
> > > > +
> > > > + /*
> > > > + * If the report is successful, the file descriptor fd is consumed
> > > > + * and closed by the Dwfl. If not, it is not closed.
> > > > + */
> > > > + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> > > > + if (!mod) {
> > > > + dwfl_end(dwfl);
> > > > + close(fd);
> > > > + return 0;
> > > > + }
> > > > +
> > > > + dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
> > > > + dso__set_a2l_libdw(dso, dwfl);
> > > > + } else {
> > > > + /* Dwfl session already initialized, get module for address. */
> > > > + mod = dwfl_addrmodule(dwfl, addr);
> > > > + }
> > > > +
> > > > + if (!mod)
> > > > + return 0;
> > > > +
> > > > + /* Find source line information for the address. */
> > > > + dwline = dwfl_module_getsrc(mod, addr);
> > > > + if (!dwline)
> > > > + return 0;
> > > > +
> > > > + /* Get line information. */
> > > > + src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
> > > > +
> > > > + if (file)
> > > > + *file = src ? strdup(src) : NULL;
> > > > + if (line_nr)
> > > > + *line_nr = lineno;
> > > > +
> > > > + /* Optionally unwind inline function call chain. */
> > > > + if (unwind_inlines && node && src) {
> > > > + Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
> > > > + Dwarf_Die *scopes = NULL;
> > > > + int nscopes;
> > > > +
> > > > + if (!cudie)
> > > > + return 1;
> > > > +
> > > > + nscopes = die_get_scopes(cudie, addr, &scopes);
> > > > + if (nscopes > 0) {
> > > > + int i;
> > > > + const char *call_file = src;
> > > > + unsigned int call_line = lineno;
> > > > +
> > > > + for (i = 0; i < nscopes; i++) {
> > > > + Dwarf_Die *die = &scopes[i];
> > > > + struct symbol *inline_sym;
> > > > + char *srcline = NULL;
> > > > + int tag = dwarf_tag(die);
> > > > +
> > > > + /* We are interested in inlined subroutines. */
> > > > + if (tag != DW_TAG_inlined_subroutine &&
> > > > + tag != DW_TAG_subprogram)
> > > > + continue;
> > > > +
> > > > + inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
> > > > +
> > > > + if (call_file)
> > > > + srcline = srcline_from_fileline(call_file, call_line);
> > > > +
> > > > + inline_list__append(inline_sym, srcline, node);
> > > > +
> > > > + /* Update call site for next level. */
> > > > + if (tag == DW_TAG_inlined_subroutine) {
> > > > + call_file = die_get_call_file(die);
> > > > + call_line = die_get_call_lineno(die);
> > > > + } else {
> > > > + /* Reached the root subprogram. */
> > > > + break;
> > > > + }
> > > > + }
> > > > + free(scopes);
> > > > + }
> > > > + }
> > > > +
> > > > + return 1;
> > > > +}
> > > > diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
> > > > new file mode 100644
> > > > index 000000000000..0f8d7b4a11a5
> > > > --- /dev/null
> > > > +++ b/tools/perf/util/libdw.h
> > > > @@ -0,0 +1,60 @@
> > > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > > +#ifndef PERF_LIBDW_H
> > > > +#define PERF_LIBDW_H
> > > > +
> > > > +#include <linux/types.h>
> > > > +
> > > > +struct dso;
> > > > +struct inline_node;
> > > > +struct symbol;
> > > > +
> > > > +#ifdef HAVE_LIBDW_SUPPORT
> > > > +/*
> > > > + * libdw__addr2line - Convert address to source location using libdw
> > > > + * @dso_name: Name of the DSO
> > > > + * @addr: Address to resolve
> > > > + * @file: Pointer to return filename (caller must free)
> > > > + * @line_nr: Pointer to return line number
> > > > + * @dso: The dso struct
> > > > + * @unwind_inlines: Whether to unwind inline function calls
> > > > + * @node: Inline node list to append to
> > > > + * @sym: The symbol associated with the address
> > > > + *
> > > > + * This function initializes a Dwfl context for the DSO if not already present,
> > > > + * finds the source line information for the given address, and optionally
> > > > + * resolves inline function call chains.
> > > > + *
> > > > + * Returns 1 on success (found), 0 on failure (not found).
> > > > + */
> > > > +int libdw__addr2line(const char *dso_name, u64 addr, char **file,
> > > > + unsigned int *line_nr, struct dso *dso,
> > > > + bool unwind_inlines, struct inline_node *node,
> > > > + struct symbol *sym);
> > > > +
> > > > +/*
> > > > + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
> > > > + * @dso: The dso to free resources for
> > > > + *
> > > > + * This function cleans up the Dwfl context used for addr2line lookups.
> > > > + */
> > > > +void dso__free_a2l_libdw(struct dso *dso);
> > > > +
> > > > +#else /* HAVE_LIBDW_SUPPORT */
> > > > +
> > > > +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
> > > > + u64 addr __maybe_unused, char **file __maybe_unused,
> > > > + unsigned int *line_nr __maybe_unused,
> > > > + struct dso *dso __maybe_unused,
> > > > + bool unwind_inlines __maybe_unused,
> > > > + struct inline_node *node __maybe_unused,
> > > > + struct symbol *sym __maybe_unused)
> > > > +{
> > > > + return 0;
> > > > +}
> > > > +
> > > > +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
> > > > +{
> > > > +}
> > > > +#endif /* HAVE_LIBDW_SUPPORT */
> > > > +
> > > > +#endif /* PERF_LIBDW_H */
> > > > diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
> > > > index 27c0966611ab..4b456c4d4138 100644
> > > > --- a/tools/perf/util/srcline.c
> > > > +++ b/tools/perf/util/srcline.c
> > > > @@ -6,6 +6,7 @@
> > > > #include "libbfd.h"
> > > > #include "llvm.h"
> > > > #include "symbol.h"
> > > > +#include "libdw.h"
> > > >
> > > > #include <inttypes.h>
> > > > #include <string.h>
> > > > @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
> > > > {
> > > > int ret;
> > > >
> > > > + ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> > > > + if (ret > 0)
> > > > + return ret;
> > > > +
> > > > ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> > > > if (ret > 0)
> > > > return ret;
> > > > --
> > > > 2.52.0.rc2.455.g230fcf2819-goog
> > > >
On 27/11/2025 11:43 am, Ian Rogers wrote:
> On Wed, Nov 26, 2025 at 10:27 AM Namhyung Kim <namhyung@kernel.org> wrote:
>>
>> On Sat, Nov 22, 2025 at 01:39:34AM -0800, Ian Rogers wrote:
>>> Add an implementation of addr2line that uses libdw. Other addr2line
>>> implementations or, in the case of forking addr2line, slow. Add an
>>> implementation that caches the libdw information in the dso and uses
>>> it to find the file and line number information.
>
> Thanks James and Namhyung for the reviews! I agree with James' comment
> about a typo in the commit message.
>
>> My concern is the limit in the open file descriptors in case the data
>> touched a lot of different libraries. The DSO code has some logic to
>> deal with it but I'm not sure if we can share that since libdw seems to
>> want to own the FD.
>
> The code opens the FD:
>
> + fd = open(dso_name, O_RDONLY);
> + if (fd < 0)
> + return 0;
> +
> + dwfl = dwfl_begin(&offline_callbacks);
> + if (!dwfl) {
> + close(fd);
> + return 0;
> + }
>
> It then uses the FD and closes it (the close is hidden in libdw itself):
>
> + /*
> + * If the report is successful, the file descriptor fd
> is consumed
> + * and closed by the Dwfl. If not, it is not closed.
> + */
> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
>
> So it is possible we exhaust all the file descriptors if there are
> multiple concurrent calls to libdw__addr2line and every dso has
> missing libdw dwfl data... but because the open/close are close
> together and that 1 FD is say small to the FDs needed for the
> cmd__addr2line, I don't think it is a problem we need to specifically
> handle. Were the FD kept open until the dso was deleted, I'd agree
> with you.
>
>> Also, have you checked if this generates the exactly same output with
>> other implementations?
>
> So the code passes `perf test` and I was checking functionality with
> perf annotate, top, etc. What I saw looked good, but it may not have
> been exhaustive. I didn't specifically create a test that compares the
> output of the different addr2line implementations. Such a test would
> be possible, it's not something we've done elsewhere.
>
> Thanks,
> Ian
>
I manually looked at a couple of line numbers and they looked
reasonable. I think an automated test that compared dwarf decoders would
be a bit of a nightmare because I'm sure there would always be subtle
differences.
Doing a manual side by side comparison of libdw__addr2line() and
llvm__addr2line(), they seem to be quite different:
$ perf record -- perf test -w leafloop
$ perf script -F ip,srcline > libdw_addr2line.txt
# Comment out libdw_addr2line() and rebuild
$ perf script -F ip,srcline > llvm_addr2line.txt
$ diff libdw_addr2line.txt llvm_addr2line.txt
It gets all of the simple leafloop workload lines the same, but lots of
the libc stuff is different.
For example libdw gives cpu-features.c:350 where llvm gives strcmp.S. At
least that one looks like inlining so llvm might be "better", but where
it gives dl-cache.c:490 isntead of llvm's mmap64.c:47, it's hard to see
how that can be inlining if they're in different compilation units.
If the llvm addr2line implementation is also supposed to be slow, it
just means we're trading speed with accuracy with this change. Hard to
say what the default should be in that case.
>> Thanks,
>> Namhyung
>>
>>>
>>> Signed-off-by: Ian Rogers <irogers@google.com>
>>> ---
>>> tools/perf/util/Build | 1 +
>>> tools/perf/util/dso.c | 2 +
>>> tools/perf/util/dso.h | 11 +++
>>> tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
>>> tools/perf/util/libdw.h | 60 +++++++++++++++++
>>> tools/perf/util/srcline.c | 5 ++
>>> 6 files changed, 215 insertions(+)
>>> create mode 100644 tools/perf/util/libdw.c
>>> create mode 100644 tools/perf/util/libdw.h
>>>
>>> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
>>> index 1c2a43e1dc68..2bed6274e248 100644
>>> --- a/tools/perf/util/Build
>>> +++ b/tools/perf/util/Build
>>> @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
>>> perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
>>> perf-util-$(CONFIG_LIBDW) += debuginfo.o
>>> perf-util-$(CONFIG_LIBDW) += annotate-data.o
>>> +perf-util-$(CONFIG_LIBDW) += libdw.o
>>>
>>> perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
>>> perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
>>> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
>>> index 344e689567ee..06980844c014 100644
>>> --- a/tools/perf/util/dso.c
>>> +++ b/tools/perf/util/dso.c
>>> @@ -32,6 +32,7 @@
>>> #include "string2.h"
>>> #include "vdso.h"
>>> #include "annotate-data.h"
>>> +#include "libdw.h"
>>>
>>> static const char * const debuglink_paths[] = {
>>> "%.0s%s",
>>> @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
>>> auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
>>> dso_cache__free(dso);
>>> dso__free_a2l(dso);
>>> + dso__free_a2l_libdw(dso);
>>> dso__free_symsrc_filename(dso);
>>> nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
>>> mutex_destroy(dso__lock(dso));
>>> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
>>> index f8ccb9816b89..4aee23775054 100644
>>> --- a/tools/perf/util/dso.h
>>> +++ b/tools/perf/util/dso.h
>>> @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
>>> const char *short_name;
>>> const char *long_name;
>>> void *a2l;
>>> + void *a2l_libdw;
>>> char *symsrc_filename;
>>> #if defined(__powerpc__)
>>> void *dwfl; /* DWARF debug info */
>>> @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
>>> RC_CHK_ACCESS(dso)->a2l = val;
>>> }
>>>
>>> +static inline void *dso__a2l_libdw(const struct dso *dso)
>>> +{
>>> + return RC_CHK_ACCESS(dso)->a2l_libdw;
>>> +}
>>> +
>>> +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
>>> +{
>>> + RC_CHK_ACCESS(dso)->a2l_libdw = val;
>>> +}
>>> +
>>> static inline unsigned int dso__a2l_fails(const struct dso *dso)
>>> {
>>> return RC_CHK_ACCESS(dso)->a2l_fails;
>>> diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
>>> new file mode 100644
>>> index 000000000000..c4331fa8e1a3
>>> --- /dev/null
>>> +++ b/tools/perf/util/libdw.c
>>> @@ -0,0 +1,136 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +#include "dso.h"
>>> +#include "libdw.h"
>>> +#include "srcline.h"
>>> +#include "symbol.h"
>>> +#include "dwarf-aux.h"
>>> +#include <fcntl.h>
>>> +#include <unistd.h>
>>> +#include <elfutils/libdwfl.h>
>>> +
>>> +void dso__free_a2l_libdw(struct dso *dso)
>>> +{
>>> + Dwfl *dwfl = dso__a2l_libdw(dso);
>>> +
>>> + if (dwfl) {
>>> + dwfl_end(dwfl);
>>> + dso__set_a2l_libdw(dso, NULL);
>>> + }
>>> +}
>>> +
>>> +int libdw__addr2line(const char *dso_name, u64 addr,
>>> + char **file, unsigned int *line_nr,
>>> + struct dso *dso, bool unwind_inlines,
>>> + struct inline_node *node, struct symbol *sym)
>>> +{
>>> + static const Dwfl_Callbacks offline_callbacks = {
>>> + .find_debuginfo = dwfl_standard_find_debuginfo,
>>> + .section_address = dwfl_offline_section_address,
>>> + .find_elf = dwfl_build_id_find_elf,
>>> + };
>>> + Dwfl *dwfl = dso__a2l_libdw(dso);
>>> + Dwfl_Module *mod;
>>> + Dwfl_Line *dwline;
>>> + Dwarf_Addr bias;
>>> + const char *src;
>>> + int lineno;
>>> +
>>> + if (!dwfl) {
>>> + /*
>>> + * Initialize Dwfl session.
>>> + * We need to open the DSO file to report it to libdw.
>>> + */
>>> + int fd;
>>> +
>>> + fd = open(dso_name, O_RDONLY);
>>> + if (fd < 0)
>>> + return 0;
>>> +
>>> + dwfl = dwfl_begin(&offline_callbacks);
>>> + if (!dwfl) {
>>> + close(fd);
>>> + return 0;
>>> + }
>>> +
>>> + /*
>>> + * If the report is successful, the file descriptor fd is consumed
>>> + * and closed by the Dwfl. If not, it is not closed.
>>> + */
>>> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
>>> + if (!mod) {
>>> + dwfl_end(dwfl);
>>> + close(fd);
>>> + return 0;
>>> + }
>>> +
>>> + dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
>>> + dso__set_a2l_libdw(dso, dwfl);
>>> + } else {
>>> + /* Dwfl session already initialized, get module for address. */
>>> + mod = dwfl_addrmodule(dwfl, addr);
>>> + }
>>> +
>>> + if (!mod)
>>> + return 0;
>>> +
>>> + /* Find source line information for the address. */
>>> + dwline = dwfl_module_getsrc(mod, addr);
>>> + if (!dwline)
>>> + return 0;
>>> +
>>> + /* Get line information. */
>>> + src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
>>> +
>>> + if (file)
>>> + *file = src ? strdup(src) : NULL;
>>> + if (line_nr)
>>> + *line_nr = lineno;
>>> +
>>> + /* Optionally unwind inline function call chain. */
>>> + if (unwind_inlines && node && src) {
>>> + Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
>>> + Dwarf_Die *scopes = NULL;
>>> + int nscopes;
>>> +
>>> + if (!cudie)
>>> + return 1;
>>> +
>>> + nscopes = die_get_scopes(cudie, addr, &scopes);
>>> + if (nscopes > 0) {
>>> + int i;
>>> + const char *call_file = src;
>>> + unsigned int call_line = lineno;
>>> +
>>> + for (i = 0; i < nscopes; i++) {
>>> + Dwarf_Die *die = &scopes[i];
>>> + struct symbol *inline_sym;
>>> + char *srcline = NULL;
>>> + int tag = dwarf_tag(die);
>>> +
>>> + /* We are interested in inlined subroutines. */
>>> + if (tag != DW_TAG_inlined_subroutine &&
>>> + tag != DW_TAG_subprogram)
>>> + continue;
>>> +
>>> + inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
>>> +
>>> + if (call_file)
>>> + srcline = srcline_from_fileline(call_file, call_line);
>>> +
>>> + inline_list__append(inline_sym, srcline, node);
>>> +
>>> + /* Update call site for next level. */
>>> + if (tag == DW_TAG_inlined_subroutine) {
>>> + call_file = die_get_call_file(die);
>>> + call_line = die_get_call_lineno(die);
>>> + } else {
>>> + /* Reached the root subprogram. */
>>> + break;
>>> + }
>>> + }
>>> + free(scopes);
>>> + }
>>> + }
>>> +
>>> + return 1;
>>> +}
>>> diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
>>> new file mode 100644
>>> index 000000000000..0f8d7b4a11a5
>>> --- /dev/null
>>> +++ b/tools/perf/util/libdw.h
>>> @@ -0,0 +1,60 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>> +#ifndef PERF_LIBDW_H
>>> +#define PERF_LIBDW_H
>>> +
>>> +#include <linux/types.h>
>>> +
>>> +struct dso;
>>> +struct inline_node;
>>> +struct symbol;
>>> +
>>> +#ifdef HAVE_LIBDW_SUPPORT
>>> +/*
>>> + * libdw__addr2line - Convert address to source location using libdw
>>> + * @dso_name: Name of the DSO
>>> + * @addr: Address to resolve
>>> + * @file: Pointer to return filename (caller must free)
>>> + * @line_nr: Pointer to return line number
>>> + * @dso: The dso struct
>>> + * @unwind_inlines: Whether to unwind inline function calls
>>> + * @node: Inline node list to append to
>>> + * @sym: The symbol associated with the address
>>> + *
>>> + * This function initializes a Dwfl context for the DSO if not already present,
>>> + * finds the source line information for the given address, and optionally
>>> + * resolves inline function call chains.
>>> + *
>>> + * Returns 1 on success (found), 0 on failure (not found).
>>> + */
>>> +int libdw__addr2line(const char *dso_name, u64 addr, char **file,
>>> + unsigned int *line_nr, struct dso *dso,
>>> + bool unwind_inlines, struct inline_node *node,
>>> + struct symbol *sym);
>>> +
>>> +/*
>>> + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
>>> + * @dso: The dso to free resources for
>>> + *
>>> + * This function cleans up the Dwfl context used for addr2line lookups.
>>> + */
>>> +void dso__free_a2l_libdw(struct dso *dso);
>>> +
>>> +#else /* HAVE_LIBDW_SUPPORT */
>>> +
>>> +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
>>> + u64 addr __maybe_unused, char **file __maybe_unused,
>>> + unsigned int *line_nr __maybe_unused,
>>> + struct dso *dso __maybe_unused,
>>> + bool unwind_inlines __maybe_unused,
>>> + struct inline_node *node __maybe_unused,
>>> + struct symbol *sym __maybe_unused)
>>> +{
>>> + return 0;
>>> +}
>>> +
>>> +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
>>> +{
>>> +}
>>> +#endif /* HAVE_LIBDW_SUPPORT */
>>> +
>>> +#endif /* PERF_LIBDW_H */
>>> diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
>>> index 27c0966611ab..4b456c4d4138 100644
>>> --- a/tools/perf/util/srcline.c
>>> +++ b/tools/perf/util/srcline.c
>>> @@ -6,6 +6,7 @@
>>> #include "libbfd.h"
>>> #include "llvm.h"
>>> #include "symbol.h"
>>> +#include "libdw.h"
>>>
>>> #include <inttypes.h>
>>> #include <string.h>
>>> @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
>>> {
>>> int ret;
>>>
>>> + ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
>>> + if (ret > 0)
>>> + return ret;
>>> +
>>> ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
>>> if (ret > 0)
>>> return ret;
>>> --
>>> 2.52.0.rc2.455.g230fcf2819-goog
>>>
On Thu, Nov 27, 2025 at 4:16 AM James Clark <james.clark@linaro.org> wrote:
>
>
>
> On 27/11/2025 11:43 am, Ian Rogers wrote:
> > On Wed, Nov 26, 2025 at 10:27 AM Namhyung Kim <namhyung@kernel.org> wrote:
> >>
> >> On Sat, Nov 22, 2025 at 01:39:34AM -0800, Ian Rogers wrote:
> >>> Add an implementation of addr2line that uses libdw. Other addr2line
> >>> implementations or, in the case of forking addr2line, slow. Add an
> >>> implementation that caches the libdw information in the dso and uses
> >>> it to find the file and line number information.
> >
> > Thanks James and Namhyung for the reviews! I agree with James' comment
> > about a typo in the commit message.
> >
> >> My concern is the limit in the open file descriptors in case the data
> >> touched a lot of different libraries. The DSO code has some logic to
> >> deal with it but I'm not sure if we can share that since libdw seems to
> >> want to own the FD.
> >
> > The code opens the FD:
> >
> > + fd = open(dso_name, O_RDONLY);
> > + if (fd < 0)
> > + return 0;
> > +
> > + dwfl = dwfl_begin(&offline_callbacks);
> > + if (!dwfl) {
> > + close(fd);
> > + return 0;
> > + }
> >
> > It then uses the FD and closes it (the close is hidden in libdw itself):
> >
> > + /*
> > + * If the report is successful, the file descriptor fd
> > is consumed
> > + * and closed by the Dwfl. If not, it is not closed.
> > + */
> > + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> >
> > So it is possible we exhaust all the file descriptors if there are
> > multiple concurrent calls to libdw__addr2line and every dso has
> > missing libdw dwfl data... but because the open/close are close
> > together and that 1 FD is say small to the FDs needed for the
> > cmd__addr2line, I don't think it is a problem we need to specifically
> > handle. Were the FD kept open until the dso was deleted, I'd agree
> > with you.
> >
> >> Also, have you checked if this generates the exactly same output with
> >> other implementations?
> >
> > So the code passes `perf test` and I was checking functionality with
> > perf annotate, top, etc. What I saw looked good, but it may not have
> > been exhaustive. I didn't specifically create a test that compares the
> > output of the different addr2line implementations. Such a test would
> > be possible, it's not something we've done elsewhere.
> >
> > Thanks,
> > Ian
> >
>
> I manually looked at a couple of line numbers and they looked
> reasonable. I think an automated test that compared dwarf decoders would
> be a bit of a nightmare because I'm sure there would always be subtle
> differences.
>
> Doing a manual side by side comparison of libdw__addr2line() and
> llvm__addr2line(), they seem to be quite different:
>
> $ perf record -- perf test -w leafloop
> $ perf script -F ip,srcline > libdw_addr2line.txt
> # Comment out libdw_addr2line() and rebuild
> $ perf script -F ip,srcline > llvm_addr2line.txt
> $ diff libdw_addr2line.txt llvm_addr2line.txt
>
> It gets all of the simple leafloop workload lines the same, but lots of
> the libc stuff is different.
>
> For example libdw gives cpu-features.c:350 where llvm gives strcmp.S. At
> least that one looks like inlining so llvm might be "better", but where
> it gives dl-cache.c:490 isntead of llvm's mmap64.c:47, it's hard to see
> how that can be inlining if they're in different compilation units.
>
> If the llvm addr2line implementation is also supposed to be slow, it
> just means we're trading speed with accuracy with this change. Hard to
> say what the default should be in that case.
Agreed. We could do some kind of option scheme like with the disassemblers:
https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/disasm.c?h=perf-tools-next#n1715
I'm not sure there are currently any distributions using the LLVM
options, this in part motivates:
https://lore.kernel.org/lkml/20251007163835.3152881-1-irogers@google.com/
but the addr2line APIs are a pain there - see the extra generated .so.
Because of that it could be reasonable to delete the LLVM addr2line
code and just focus on libdw. I kind of wish we could also delete the
precarious command forking versions too. And libbfd... Perhaps with
this code, those advocating libbfd have a fast enough alternative
without bringing in large dependencies like libLLVM.
Thanks,
Ian
> >> Thanks,
> >> Namhyung
> >>
> >>>
> >>> Signed-off-by: Ian Rogers <irogers@google.com>
> >>> ---
> >>> tools/perf/util/Build | 1 +
> >>> tools/perf/util/dso.c | 2 +
> >>> tools/perf/util/dso.h | 11 +++
> >>> tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
> >>> tools/perf/util/libdw.h | 60 +++++++++++++++++
> >>> tools/perf/util/srcline.c | 5 ++
> >>> 6 files changed, 215 insertions(+)
> >>> create mode 100644 tools/perf/util/libdw.c
> >>> create mode 100644 tools/perf/util/libdw.h
> >>>
> >>> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> >>> index 1c2a43e1dc68..2bed6274e248 100644
> >>> --- a/tools/perf/util/Build
> >>> +++ b/tools/perf/util/Build
> >>> @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
> >>> perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
> >>> perf-util-$(CONFIG_LIBDW) += debuginfo.o
> >>> perf-util-$(CONFIG_LIBDW) += annotate-data.o
> >>> +perf-util-$(CONFIG_LIBDW) += libdw.o
> >>>
> >>> perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
> >>> perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
> >>> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> >>> index 344e689567ee..06980844c014 100644
> >>> --- a/tools/perf/util/dso.c
> >>> +++ b/tools/perf/util/dso.c
> >>> @@ -32,6 +32,7 @@
> >>> #include "string2.h"
> >>> #include "vdso.h"
> >>> #include "annotate-data.h"
> >>> +#include "libdw.h"
> >>>
> >>> static const char * const debuglink_paths[] = {
> >>> "%.0s%s",
> >>> @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
> >>> auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
> >>> dso_cache__free(dso);
> >>> dso__free_a2l(dso);
> >>> + dso__free_a2l_libdw(dso);
> >>> dso__free_symsrc_filename(dso);
> >>> nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
> >>> mutex_destroy(dso__lock(dso));
> >>> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> >>> index f8ccb9816b89..4aee23775054 100644
> >>> --- a/tools/perf/util/dso.h
> >>> +++ b/tools/perf/util/dso.h
> >>> @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
> >>> const char *short_name;
> >>> const char *long_name;
> >>> void *a2l;
> >>> + void *a2l_libdw;
> >>> char *symsrc_filename;
> >>> #if defined(__powerpc__)
> >>> void *dwfl; /* DWARF debug info */
> >>> @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
> >>> RC_CHK_ACCESS(dso)->a2l = val;
> >>> }
> >>>
> >>> +static inline void *dso__a2l_libdw(const struct dso *dso)
> >>> +{
> >>> + return RC_CHK_ACCESS(dso)->a2l_libdw;
> >>> +}
> >>> +
> >>> +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
> >>> +{
> >>> + RC_CHK_ACCESS(dso)->a2l_libdw = val;
> >>> +}
> >>> +
> >>> static inline unsigned int dso__a2l_fails(const struct dso *dso)
> >>> {
> >>> return RC_CHK_ACCESS(dso)->a2l_fails;
> >>> diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
> >>> new file mode 100644
> >>> index 000000000000..c4331fa8e1a3
> >>> --- /dev/null
> >>> +++ b/tools/perf/util/libdw.c
> >>> @@ -0,0 +1,136 @@
> >>> +// SPDX-License-Identifier: GPL-2.0
> >>> +#include "dso.h"
> >>> +#include "libdw.h"
> >>> +#include "srcline.h"
> >>> +#include "symbol.h"
> >>> +#include "dwarf-aux.h"
> >>> +#include <fcntl.h>
> >>> +#include <unistd.h>
> >>> +#include <elfutils/libdwfl.h>
> >>> +
> >>> +void dso__free_a2l_libdw(struct dso *dso)
> >>> +{
> >>> + Dwfl *dwfl = dso__a2l_libdw(dso);
> >>> +
> >>> + if (dwfl) {
> >>> + dwfl_end(dwfl);
> >>> + dso__set_a2l_libdw(dso, NULL);
> >>> + }
> >>> +}
> >>> +
> >>> +int libdw__addr2line(const char *dso_name, u64 addr,
> >>> + char **file, unsigned int *line_nr,
> >>> + struct dso *dso, bool unwind_inlines,
> >>> + struct inline_node *node, struct symbol *sym)
> >>> +{
> >>> + static const Dwfl_Callbacks offline_callbacks = {
> >>> + .find_debuginfo = dwfl_standard_find_debuginfo,
> >>> + .section_address = dwfl_offline_section_address,
> >>> + .find_elf = dwfl_build_id_find_elf,
> >>> + };
> >>> + Dwfl *dwfl = dso__a2l_libdw(dso);
> >>> + Dwfl_Module *mod;
> >>> + Dwfl_Line *dwline;
> >>> + Dwarf_Addr bias;
> >>> + const char *src;
> >>> + int lineno;
> >>> +
> >>> + if (!dwfl) {
> >>> + /*
> >>> + * Initialize Dwfl session.
> >>> + * We need to open the DSO file to report it to libdw.
> >>> + */
> >>> + int fd;
> >>> +
> >>> + fd = open(dso_name, O_RDONLY);
> >>> + if (fd < 0)
> >>> + return 0;
> >>> +
> >>> + dwfl = dwfl_begin(&offline_callbacks);
> >>> + if (!dwfl) {
> >>> + close(fd);
> >>> + return 0;
> >>> + }
> >>> +
> >>> + /*
> >>> + * If the report is successful, the file descriptor fd is consumed
> >>> + * and closed by the Dwfl. If not, it is not closed.
> >>> + */
> >>> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> >>> + if (!mod) {
> >>> + dwfl_end(dwfl);
> >>> + close(fd);
> >>> + return 0;
> >>> + }
> >>> +
> >>> + dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
> >>> + dso__set_a2l_libdw(dso, dwfl);
> >>> + } else {
> >>> + /* Dwfl session already initialized, get module for address. */
> >>> + mod = dwfl_addrmodule(dwfl, addr);
> >>> + }
> >>> +
> >>> + if (!mod)
> >>> + return 0;
> >>> +
> >>> + /* Find source line information for the address. */
> >>> + dwline = dwfl_module_getsrc(mod, addr);
> >>> + if (!dwline)
> >>> + return 0;
> >>> +
> >>> + /* Get line information. */
> >>> + src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
> >>> +
> >>> + if (file)
> >>> + *file = src ? strdup(src) : NULL;
> >>> + if (line_nr)
> >>> + *line_nr = lineno;
> >>> +
> >>> + /* Optionally unwind inline function call chain. */
> >>> + if (unwind_inlines && node && src) {
> >>> + Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
> >>> + Dwarf_Die *scopes = NULL;
> >>> + int nscopes;
> >>> +
> >>> + if (!cudie)
> >>> + return 1;
> >>> +
> >>> + nscopes = die_get_scopes(cudie, addr, &scopes);
> >>> + if (nscopes > 0) {
> >>> + int i;
> >>> + const char *call_file = src;
> >>> + unsigned int call_line = lineno;
> >>> +
> >>> + for (i = 0; i < nscopes; i++) {
> >>> + Dwarf_Die *die = &scopes[i];
> >>> + struct symbol *inline_sym;
> >>> + char *srcline = NULL;
> >>> + int tag = dwarf_tag(die);
> >>> +
> >>> + /* We are interested in inlined subroutines. */
> >>> + if (tag != DW_TAG_inlined_subroutine &&
> >>> + tag != DW_TAG_subprogram)
> >>> + continue;
> >>> +
> >>> + inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
> >>> +
> >>> + if (call_file)
> >>> + srcline = srcline_from_fileline(call_file, call_line);
> >>> +
> >>> + inline_list__append(inline_sym, srcline, node);
> >>> +
> >>> + /* Update call site for next level. */
> >>> + if (tag == DW_TAG_inlined_subroutine) {
> >>> + call_file = die_get_call_file(die);
> >>> + call_line = die_get_call_lineno(die);
> >>> + } else {
> >>> + /* Reached the root subprogram. */
> >>> + break;
> >>> + }
> >>> + }
> >>> + free(scopes);
> >>> + }
> >>> + }
> >>> +
> >>> + return 1;
> >>> +}
> >>> diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
> >>> new file mode 100644
> >>> index 000000000000..0f8d7b4a11a5
> >>> --- /dev/null
> >>> +++ b/tools/perf/util/libdw.h
> >>> @@ -0,0 +1,60 @@
> >>> +/* SPDX-License-Identifier: GPL-2.0 */
> >>> +#ifndef PERF_LIBDW_H
> >>> +#define PERF_LIBDW_H
> >>> +
> >>> +#include <linux/types.h>
> >>> +
> >>> +struct dso;
> >>> +struct inline_node;
> >>> +struct symbol;
> >>> +
> >>> +#ifdef HAVE_LIBDW_SUPPORT
> >>> +/*
> >>> + * libdw__addr2line - Convert address to source location using libdw
> >>> + * @dso_name: Name of the DSO
> >>> + * @addr: Address to resolve
> >>> + * @file: Pointer to return filename (caller must free)
> >>> + * @line_nr: Pointer to return line number
> >>> + * @dso: The dso struct
> >>> + * @unwind_inlines: Whether to unwind inline function calls
> >>> + * @node: Inline node list to append to
> >>> + * @sym: The symbol associated with the address
> >>> + *
> >>> + * This function initializes a Dwfl context for the DSO if not already present,
> >>> + * finds the source line information for the given address, and optionally
> >>> + * resolves inline function call chains.
> >>> + *
> >>> + * Returns 1 on success (found), 0 on failure (not found).
> >>> + */
> >>> +int libdw__addr2line(const char *dso_name, u64 addr, char **file,
> >>> + unsigned int *line_nr, struct dso *dso,
> >>> + bool unwind_inlines, struct inline_node *node,
> >>> + struct symbol *sym);
> >>> +
> >>> +/*
> >>> + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
> >>> + * @dso: The dso to free resources for
> >>> + *
> >>> + * This function cleans up the Dwfl context used for addr2line lookups.
> >>> + */
> >>> +void dso__free_a2l_libdw(struct dso *dso);
> >>> +
> >>> +#else /* HAVE_LIBDW_SUPPORT */
> >>> +
> >>> +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
> >>> + u64 addr __maybe_unused, char **file __maybe_unused,
> >>> + unsigned int *line_nr __maybe_unused,
> >>> + struct dso *dso __maybe_unused,
> >>> + bool unwind_inlines __maybe_unused,
> >>> + struct inline_node *node __maybe_unused,
> >>> + struct symbol *sym __maybe_unused)
> >>> +{
> >>> + return 0;
> >>> +}
> >>> +
> >>> +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
> >>> +{
> >>> +}
> >>> +#endif /* HAVE_LIBDW_SUPPORT */
> >>> +
> >>> +#endif /* PERF_LIBDW_H */
> >>> diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
> >>> index 27c0966611ab..4b456c4d4138 100644
> >>> --- a/tools/perf/util/srcline.c
> >>> +++ b/tools/perf/util/srcline.c
> >>> @@ -6,6 +6,7 @@
> >>> #include "libbfd.h"
> >>> #include "llvm.h"
> >>> #include "symbol.h"
> >>> +#include "libdw.h"
> >>>
> >>> #include <inttypes.h>
> >>> #include <string.h>
> >>> @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
> >>> {
> >>> int ret;
> >>>
> >>> + ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> >>> + if (ret > 0)
> >>> + return ret;
> >>> +
> >>> ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> >>> if (ret > 0)
> >>> return ret;
> >>> --
> >>> 2.52.0.rc2.455.g230fcf2819-goog
> >>>
>
On 27/11/2025 1:19 pm, Ian Rogers wrote:
> On Thu, Nov 27, 2025 at 4:16 AM James Clark <james.clark@linaro.org> wrote:
>>
>>
>>
>> On 27/11/2025 11:43 am, Ian Rogers wrote:
>>> On Wed, Nov 26, 2025 at 10:27 AM Namhyung Kim <namhyung@kernel.org> wrote:
>>>>
>>>> On Sat, Nov 22, 2025 at 01:39:34AM -0800, Ian Rogers wrote:
>>>>> Add an implementation of addr2line that uses libdw. Other addr2line
>>>>> implementations or, in the case of forking addr2line, slow. Add an
>>>>> implementation that caches the libdw information in the dso and uses
>>>>> it to find the file and line number information.
>>>
>>> Thanks James and Namhyung for the reviews! I agree with James' comment
>>> about a typo in the commit message.
>>>
>>>> My concern is the limit in the open file descriptors in case the data
>>>> touched a lot of different libraries. The DSO code has some logic to
>>>> deal with it but I'm not sure if we can share that since libdw seems to
>>>> want to own the FD.
>>>
>>> The code opens the FD:
>>>
>>> + fd = open(dso_name, O_RDONLY);
>>> + if (fd < 0)
>>> + return 0;
>>> +
>>> + dwfl = dwfl_begin(&offline_callbacks);
>>> + if (!dwfl) {
>>> + close(fd);
>>> + return 0;
>>> + }
>>>
>>> It then uses the FD and closes it (the close is hidden in libdw itself):
>>>
>>> + /*
>>> + * If the report is successful, the file descriptor fd
>>> is consumed
>>> + * and closed by the Dwfl. If not, it is not closed.
>>> + */
>>> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
>>>
>>> So it is possible we exhaust all the file descriptors if there are
>>> multiple concurrent calls to libdw__addr2line and every dso has
>>> missing libdw dwfl data... but because the open/close are close
>>> together and that 1 FD is say small to the FDs needed for the
>>> cmd__addr2line, I don't think it is a problem we need to specifically
>>> handle. Were the FD kept open until the dso was deleted, I'd agree
>>> with you.
>>>
>>>> Also, have you checked if this generates the exactly same output with
>>>> other implementations?
>>>
>>> So the code passes `perf test` and I was checking functionality with
>>> perf annotate, top, etc. What I saw looked good, but it may not have
>>> been exhaustive. I didn't specifically create a test that compares the
>>> output of the different addr2line implementations. Such a test would
>>> be possible, it's not something we've done elsewhere.
>>>
>>> Thanks,
>>> Ian
>>>
>>
>> I manually looked at a couple of line numbers and they looked
>> reasonable. I think an automated test that compared dwarf decoders would
>> be a bit of a nightmare because I'm sure there would always be subtle
>> differences.
>>
>> Doing a manual side by side comparison of libdw__addr2line() and
>> llvm__addr2line(), they seem to be quite different:
>>
>> $ perf record -- perf test -w leafloop
>> $ perf script -F ip,srcline > libdw_addr2line.txt
>> # Comment out libdw_addr2line() and rebuild
>> $ perf script -F ip,srcline > llvm_addr2line.txt
>> $ diff libdw_addr2line.txt llvm_addr2line.txt
>>
>> It gets all of the simple leafloop workload lines the same, but lots of
>> the libc stuff is different.
>>
>> For example libdw gives cpu-features.c:350 where llvm gives strcmp.S. At
>> least that one looks like inlining so llvm might be "better", but where
>> it gives dl-cache.c:490 isntead of llvm's mmap64.c:47, it's hard to see
>> how that can be inlining if they're in different compilation units.
>>
>> If the llvm addr2line implementation is also supposed to be slow, it
>> just means we're trading speed with accuracy with this change. Hard to
>> say what the default should be in that case.
>
> Agreed. We could do some kind of option scheme like with the disassemblers:
> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/disasm.c?h=perf-tools-next#n1715
>
> I'm not sure there are currently any distributions using the LLVM
> options, this in part motivates:
> https://lore.kernel.org/lkml/20251007163835.3152881-1-irogers@google.com/
> but the addr2line APIs are a pain there - see the extra generated .so.
> Because of that it could be reasonable to delete the LLVM addr2line
> code and just focus on libdw. I kind of wish we could also delete the
> precarious command forking versions too. And libbfd... Perhaps with
> this code, those advocating libbfd have a fast enough alternative
> without bringing in large dependencies like libLLVM.
>
> Thanks,
> Ian
>
Personally for debugging I would want the most accurate and detailed
information possible and don't care at all about the size of
dependencies. If Perf is a tool for debugging then surely that should be
the default? But right now I don't actually know which of the outputs is
most accurate although I'll assume that the llvm one is.
Wanting the smallest application possible while trading away detail and
accuracy seems like an unusual special case that should be opt in. It
also seems to relate to this old discussion [1], in that if we're going
to keep the llvm depencency then it doesn't make sense to re-write
anything in Perf.
[1]:
https://lore.kernel.org/linux-perf-users/549d3812-a606-4981-83f5-0a99b0ff9f6a@linaro.org/
>>>> Thanks,
>>>> Namhyung
>>>>
>>>>>
>>>>> Signed-off-by: Ian Rogers <irogers@google.com>
>>>>> ---
>>>>> tools/perf/util/Build | 1 +
>>>>> tools/perf/util/dso.c | 2 +
>>>>> tools/perf/util/dso.h | 11 +++
>>>>> tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
>>>>> tools/perf/util/libdw.h | 60 +++++++++++++++++
>>>>> tools/perf/util/srcline.c | 5 ++
>>>>> 6 files changed, 215 insertions(+)
>>>>> create mode 100644 tools/perf/util/libdw.c
>>>>> create mode 100644 tools/perf/util/libdw.h
>>>>>
>>>>> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
>>>>> index 1c2a43e1dc68..2bed6274e248 100644
>>>>> --- a/tools/perf/util/Build
>>>>> +++ b/tools/perf/util/Build
>>>>> @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
>>>>> perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
>>>>> perf-util-$(CONFIG_LIBDW) += debuginfo.o
>>>>> perf-util-$(CONFIG_LIBDW) += annotate-data.o
>>>>> +perf-util-$(CONFIG_LIBDW) += libdw.o
>>>>>
>>>>> perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
>>>>> perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
>>>>> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
>>>>> index 344e689567ee..06980844c014 100644
>>>>> --- a/tools/perf/util/dso.c
>>>>> +++ b/tools/perf/util/dso.c
>>>>> @@ -32,6 +32,7 @@
>>>>> #include "string2.h"
>>>>> #include "vdso.h"
>>>>> #include "annotate-data.h"
>>>>> +#include "libdw.h"
>>>>>
>>>>> static const char * const debuglink_paths[] = {
>>>>> "%.0s%s",
>>>>> @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
>>>>> auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
>>>>> dso_cache__free(dso);
>>>>> dso__free_a2l(dso);
>>>>> + dso__free_a2l_libdw(dso);
>>>>> dso__free_symsrc_filename(dso);
>>>>> nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
>>>>> mutex_destroy(dso__lock(dso));
>>>>> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
>>>>> index f8ccb9816b89..4aee23775054 100644
>>>>> --- a/tools/perf/util/dso.h
>>>>> +++ b/tools/perf/util/dso.h
>>>>> @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
>>>>> const char *short_name;
>>>>> const char *long_name;
>>>>> void *a2l;
>>>>> + void *a2l_libdw;
>>>>> char *symsrc_filename;
>>>>> #if defined(__powerpc__)
>>>>> void *dwfl; /* DWARF debug info */
>>>>> @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
>>>>> RC_CHK_ACCESS(dso)->a2l = val;
>>>>> }
>>>>>
>>>>> +static inline void *dso__a2l_libdw(const struct dso *dso)
>>>>> +{
>>>>> + return RC_CHK_ACCESS(dso)->a2l_libdw;
>>>>> +}
>>>>> +
>>>>> +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
>>>>> +{
>>>>> + RC_CHK_ACCESS(dso)->a2l_libdw = val;
>>>>> +}
>>>>> +
>>>>> static inline unsigned int dso__a2l_fails(const struct dso *dso)
>>>>> {
>>>>> return RC_CHK_ACCESS(dso)->a2l_fails;
>>>>> diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
>>>>> new file mode 100644
>>>>> index 000000000000..c4331fa8e1a3
>>>>> --- /dev/null
>>>>> +++ b/tools/perf/util/libdw.c
>>>>> @@ -0,0 +1,136 @@
>>>>> +// SPDX-License-Identifier: GPL-2.0
>>>>> +#include "dso.h"
>>>>> +#include "libdw.h"
>>>>> +#include "srcline.h"
>>>>> +#include "symbol.h"
>>>>> +#include "dwarf-aux.h"
>>>>> +#include <fcntl.h>
>>>>> +#include <unistd.h>
>>>>> +#include <elfutils/libdwfl.h>
>>>>> +
>>>>> +void dso__free_a2l_libdw(struct dso *dso)
>>>>> +{
>>>>> + Dwfl *dwfl = dso__a2l_libdw(dso);
>>>>> +
>>>>> + if (dwfl) {
>>>>> + dwfl_end(dwfl);
>>>>> + dso__set_a2l_libdw(dso, NULL);
>>>>> + }
>>>>> +}
>>>>> +
>>>>> +int libdw__addr2line(const char *dso_name, u64 addr,
>>>>> + char **file, unsigned int *line_nr,
>>>>> + struct dso *dso, bool unwind_inlines,
>>>>> + struct inline_node *node, struct symbol *sym)
>>>>> +{
>>>>> + static const Dwfl_Callbacks offline_callbacks = {
>>>>> + .find_debuginfo = dwfl_standard_find_debuginfo,
>>>>> + .section_address = dwfl_offline_section_address,
>>>>> + .find_elf = dwfl_build_id_find_elf,
>>>>> + };
>>>>> + Dwfl *dwfl = dso__a2l_libdw(dso);
>>>>> + Dwfl_Module *mod;
>>>>> + Dwfl_Line *dwline;
>>>>> + Dwarf_Addr bias;
>>>>> + const char *src;
>>>>> + int lineno;
>>>>> +
>>>>> + if (!dwfl) {
>>>>> + /*
>>>>> + * Initialize Dwfl session.
>>>>> + * We need to open the DSO file to report it to libdw.
>>>>> + */
>>>>> + int fd;
>>>>> +
>>>>> + fd = open(dso_name, O_RDONLY);
>>>>> + if (fd < 0)
>>>>> + return 0;
>>>>> +
>>>>> + dwfl = dwfl_begin(&offline_callbacks);
>>>>> + if (!dwfl) {
>>>>> + close(fd);
>>>>> + return 0;
>>>>> + }
>>>>> +
>>>>> + /*
>>>>> + * If the report is successful, the file descriptor fd is consumed
>>>>> + * and closed by the Dwfl. If not, it is not closed.
>>>>> + */
>>>>> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
>>>>> + if (!mod) {
>>>>> + dwfl_end(dwfl);
>>>>> + close(fd);
>>>>> + return 0;
>>>>> + }
>>>>> +
>>>>> + dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
>>>>> + dso__set_a2l_libdw(dso, dwfl);
>>>>> + } else {
>>>>> + /* Dwfl session already initialized, get module for address. */
>>>>> + mod = dwfl_addrmodule(dwfl, addr);
>>>>> + }
>>>>> +
>>>>> + if (!mod)
>>>>> + return 0;
>>>>> +
>>>>> + /* Find source line information for the address. */
>>>>> + dwline = dwfl_module_getsrc(mod, addr);
>>>>> + if (!dwline)
>>>>> + return 0;
>>>>> +
>>>>> + /* Get line information. */
>>>>> + src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
>>>>> +
>>>>> + if (file)
>>>>> + *file = src ? strdup(src) : NULL;
>>>>> + if (line_nr)
>>>>> + *line_nr = lineno;
>>>>> +
>>>>> + /* Optionally unwind inline function call chain. */
>>>>> + if (unwind_inlines && node && src) {
>>>>> + Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
>>>>> + Dwarf_Die *scopes = NULL;
>>>>> + int nscopes;
>>>>> +
>>>>> + if (!cudie)
>>>>> + return 1;
>>>>> +
>>>>> + nscopes = die_get_scopes(cudie, addr, &scopes);
>>>>> + if (nscopes > 0) {
>>>>> + int i;
>>>>> + const char *call_file = src;
>>>>> + unsigned int call_line = lineno;
>>>>> +
>>>>> + for (i = 0; i < nscopes; i++) {
>>>>> + Dwarf_Die *die = &scopes[i];
>>>>> + struct symbol *inline_sym;
>>>>> + char *srcline = NULL;
>>>>> + int tag = dwarf_tag(die);
>>>>> +
>>>>> + /* We are interested in inlined subroutines. */
>>>>> + if (tag != DW_TAG_inlined_subroutine &&
>>>>> + tag != DW_TAG_subprogram)
>>>>> + continue;
>>>>> +
>>>>> + inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
>>>>> +
>>>>> + if (call_file)
>>>>> + srcline = srcline_from_fileline(call_file, call_line);
>>>>> +
>>>>> + inline_list__append(inline_sym, srcline, node);
>>>>> +
>>>>> + /* Update call site for next level. */
>>>>> + if (tag == DW_TAG_inlined_subroutine) {
>>>>> + call_file = die_get_call_file(die);
>>>>> + call_line = die_get_call_lineno(die);
>>>>> + } else {
>>>>> + /* Reached the root subprogram. */
>>>>> + break;
>>>>> + }
>>>>> + }
>>>>> + free(scopes);
>>>>> + }
>>>>> + }
>>>>> +
>>>>> + return 1;
>>>>> +}
>>>>> diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
>>>>> new file mode 100644
>>>>> index 000000000000..0f8d7b4a11a5
>>>>> --- /dev/null
>>>>> +++ b/tools/perf/util/libdw.h
>>>>> @@ -0,0 +1,60 @@
>>>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>>>> +#ifndef PERF_LIBDW_H
>>>>> +#define PERF_LIBDW_H
>>>>> +
>>>>> +#include <linux/types.h>
>>>>> +
>>>>> +struct dso;
>>>>> +struct inline_node;
>>>>> +struct symbol;
>>>>> +
>>>>> +#ifdef HAVE_LIBDW_SUPPORT
>>>>> +/*
>>>>> + * libdw__addr2line - Convert address to source location using libdw
>>>>> + * @dso_name: Name of the DSO
>>>>> + * @addr: Address to resolve
>>>>> + * @file: Pointer to return filename (caller must free)
>>>>> + * @line_nr: Pointer to return line number
>>>>> + * @dso: The dso struct
>>>>> + * @unwind_inlines: Whether to unwind inline function calls
>>>>> + * @node: Inline node list to append to
>>>>> + * @sym: The symbol associated with the address
>>>>> + *
>>>>> + * This function initializes a Dwfl context for the DSO if not already present,
>>>>> + * finds the source line information for the given address, and optionally
>>>>> + * resolves inline function call chains.
>>>>> + *
>>>>> + * Returns 1 on success (found), 0 on failure (not found).
>>>>> + */
>>>>> +int libdw__addr2line(const char *dso_name, u64 addr, char **file,
>>>>> + unsigned int *line_nr, struct dso *dso,
>>>>> + bool unwind_inlines, struct inline_node *node,
>>>>> + struct symbol *sym);
>>>>> +
>>>>> +/*
>>>>> + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
>>>>> + * @dso: The dso to free resources for
>>>>> + *
>>>>> + * This function cleans up the Dwfl context used for addr2line lookups.
>>>>> + */
>>>>> +void dso__free_a2l_libdw(struct dso *dso);
>>>>> +
>>>>> +#else /* HAVE_LIBDW_SUPPORT */
>>>>> +
>>>>> +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
>>>>> + u64 addr __maybe_unused, char **file __maybe_unused,
>>>>> + unsigned int *line_nr __maybe_unused,
>>>>> + struct dso *dso __maybe_unused,
>>>>> + bool unwind_inlines __maybe_unused,
>>>>> + struct inline_node *node __maybe_unused,
>>>>> + struct symbol *sym __maybe_unused)
>>>>> +{
>>>>> + return 0;
>>>>> +}
>>>>> +
>>>>> +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
>>>>> +{
>>>>> +}
>>>>> +#endif /* HAVE_LIBDW_SUPPORT */
>>>>> +
>>>>> +#endif /* PERF_LIBDW_H */
>>>>> diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
>>>>> index 27c0966611ab..4b456c4d4138 100644
>>>>> --- a/tools/perf/util/srcline.c
>>>>> +++ b/tools/perf/util/srcline.c
>>>>> @@ -6,6 +6,7 @@
>>>>> #include "libbfd.h"
>>>>> #include "llvm.h"
>>>>> #include "symbol.h"
>>>>> +#include "libdw.h"
>>>>>
>>>>> #include <inttypes.h>
>>>>> #include <string.h>
>>>>> @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
>>>>> {
>>>>> int ret;
>>>>>
>>>>> + ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
>>>>> + if (ret > 0)
>>>>> + return ret;
>>>>> +
>>>>> ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
>>>>> if (ret > 0)
>>>>> return ret;
>>>>> --
>>>>> 2.52.0.rc2.455.g230fcf2819-goog
>>>>>
>>
On Thu, Nov 27, 2025 at 5:48 AM James Clark <james.clark@linaro.org> wrote:
>
>
>
> On 27/11/2025 1:19 pm, Ian Rogers wrote:
> > On Thu, Nov 27, 2025 at 4:16 AM James Clark <james.clark@linaro.org> wrote:
> >>
> >>
> >>
> >> On 27/11/2025 11:43 am, Ian Rogers wrote:
> >>> On Wed, Nov 26, 2025 at 10:27 AM Namhyung Kim <namhyung@kernel.org> wrote:
> >>>>
> >>>> On Sat, Nov 22, 2025 at 01:39:34AM -0800, Ian Rogers wrote:
> >>>>> Add an implementation of addr2line that uses libdw. Other addr2line
> >>>>> implementations or, in the case of forking addr2line, slow. Add an
> >>>>> implementation that caches the libdw information in the dso and uses
> >>>>> it to find the file and line number information.
> >>>
> >>> Thanks James and Namhyung for the reviews! I agree with James' comment
> >>> about a typo in the commit message.
> >>>
> >>>> My concern is the limit in the open file descriptors in case the data
> >>>> touched a lot of different libraries. The DSO code has some logic to
> >>>> deal with it but I'm not sure if we can share that since libdw seems to
> >>>> want to own the FD.
> >>>
> >>> The code opens the FD:
> >>>
> >>> + fd = open(dso_name, O_RDONLY);
> >>> + if (fd < 0)
> >>> + return 0;
> >>> +
> >>> + dwfl = dwfl_begin(&offline_callbacks);
> >>> + if (!dwfl) {
> >>> + close(fd);
> >>> + return 0;
> >>> + }
> >>>
> >>> It then uses the FD and closes it (the close is hidden in libdw itself):
> >>>
> >>> + /*
> >>> + * If the report is successful, the file descriptor fd
> >>> is consumed
> >>> + * and closed by the Dwfl. If not, it is not closed.
> >>> + */
> >>> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> >>>
> >>> So it is possible we exhaust all the file descriptors if there are
> >>> multiple concurrent calls to libdw__addr2line and every dso has
> >>> missing libdw dwfl data... but because the open/close are close
> >>> together and that 1 FD is say small to the FDs needed for the
> >>> cmd__addr2line, I don't think it is a problem we need to specifically
> >>> handle. Were the FD kept open until the dso was deleted, I'd agree
> >>> with you.
> >>>
> >>>> Also, have you checked if this generates the exactly same output with
> >>>> other implementations?
> >>>
> >>> So the code passes `perf test` and I was checking functionality with
> >>> perf annotate, top, etc. What I saw looked good, but it may not have
> >>> been exhaustive. I didn't specifically create a test that compares the
> >>> output of the different addr2line implementations. Such a test would
> >>> be possible, it's not something we've done elsewhere.
> >>>
> >>> Thanks,
> >>> Ian
> >>>
> >>
> >> I manually looked at a couple of line numbers and they looked
> >> reasonable. I think an automated test that compared dwarf decoders would
> >> be a bit of a nightmare because I'm sure there would always be subtle
> >> differences.
> >>
> >> Doing a manual side by side comparison of libdw__addr2line() and
> >> llvm__addr2line(), they seem to be quite different:
> >>
> >> $ perf record -- perf test -w leafloop
> >> $ perf script -F ip,srcline > libdw_addr2line.txt
> >> # Comment out libdw_addr2line() and rebuild
> >> $ perf script -F ip,srcline > llvm_addr2line.txt
> >> $ diff libdw_addr2line.txt llvm_addr2line.txt
> >>
> >> It gets all of the simple leafloop workload lines the same, but lots of
> >> the libc stuff is different.
> >>
> >> For example libdw gives cpu-features.c:350 where llvm gives strcmp.S. At
> >> least that one looks like inlining so llvm might be "better", but where
> >> it gives dl-cache.c:490 isntead of llvm's mmap64.c:47, it's hard to see
> >> how that can be inlining if they're in different compilation units.
> >>
> >> If the llvm addr2line implementation is also supposed to be slow, it
> >> just means we're trading speed with accuracy with this change. Hard to
> >> say what the default should be in that case.
> >
> > Agreed. We could do some kind of option scheme like with the disassemblers:
> > https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/disasm.c?h=perf-tools-next#n1715
> >
> > I'm not sure there are currently any distributions using the LLVM
> > options, this in part motivates:
> > https://lore.kernel.org/lkml/20251007163835.3152881-1-irogers@google.com/
> > but the addr2line APIs are a pain there - see the extra generated .so.
> > Because of that it could be reasonable to delete the LLVM addr2line
> > code and just focus on libdw. I kind of wish we could also delete the
> > precarious command forking versions too. And libbfd... Perhaps with
> > this code, those advocating libbfd have a fast enough alternative
> > without bringing in large dependencies like libLLVM.
> >
> > Thanks,
> > Ian
> >
>
> Personally for debugging I would want the most accurate and detailed
> information possible and don't care at all about the size of
> dependencies. If Perf is a tool for debugging then surely that should be
> the default? But right now I don't actually know which of the outputs is
> most accurate although I'll assume that the llvm one is.
I know LLVM got dwarf 5 support early. I'm not sure if accurate is the
best word to compare libdw and LLVM as, if libdw supports the format,
discrepancies are bugs in LLVM or libdw, .. Building around LLVM as a
common base sgtm and my main use-case doesn't get impeded by the large
dependency because of the dlopen patches. As libelf/libdw is pretty
much a given for a perf build, as it is required for libbpf, then the
code here can avoid the fork/exec fallback. I can see the sense in
trying with LLVM first and then falling back to libdw.
> Wanting the smallest application possible while trading away detail and
> accuracy seems like an unusual special case that should be opt in. It
> also seems to relate to this old discussion [1], in that if we're going
> to keep the llvm depencency then it doesn't make sense to re-write
> anything in Perf.
So I think PE support in libdw wouldn't be a priority and so LLVM for
the win there. I think distributions have been slow to pick up the
LLVM dependency, I'm not sure what the issue is there. It would be
nice to start removing some of the alternatives the perf build
supports. The libbfd and libunwind code is only built with specific
opt-ins, and I think the fork/exec addr2line is redundant after this
change. For addr2line that'd bring the 2 implementations down to libdw
and LLVM. As the recent libbfd fixes show [1], inadvertently we can
break these largely untested dependencies by exposing latent bugs in
things like improper initialization.
Thanks,
Ian
[1] https://lore.kernel.org/lkml/20251112074311.1440101-1-irogers@google.com/
> [1]:
> https://lore.kernel.org/linux-perf-users/549d3812-a606-4981-83f5-0a99b0ff9f6a@linaro.org/
>
> >>>> Thanks,
> >>>> Namhyung
> >>>>
> >>>>>
> >>>>> Signed-off-by: Ian Rogers <irogers@google.com>
> >>>>> ---
> >>>>> tools/perf/util/Build | 1 +
> >>>>> tools/perf/util/dso.c | 2 +
> >>>>> tools/perf/util/dso.h | 11 +++
> >>>>> tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
> >>>>> tools/perf/util/libdw.h | 60 +++++++++++++++++
> >>>>> tools/perf/util/srcline.c | 5 ++
> >>>>> 6 files changed, 215 insertions(+)
> >>>>> create mode 100644 tools/perf/util/libdw.c
> >>>>> create mode 100644 tools/perf/util/libdw.h
> >>>>>
> >>>>> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> >>>>> index 1c2a43e1dc68..2bed6274e248 100644
> >>>>> --- a/tools/perf/util/Build
> >>>>> +++ b/tools/perf/util/Build
> >>>>> @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
> >>>>> perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
> >>>>> perf-util-$(CONFIG_LIBDW) += debuginfo.o
> >>>>> perf-util-$(CONFIG_LIBDW) += annotate-data.o
> >>>>> +perf-util-$(CONFIG_LIBDW) += libdw.o
> >>>>>
> >>>>> perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
> >>>>> perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
> >>>>> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> >>>>> index 344e689567ee..06980844c014 100644
> >>>>> --- a/tools/perf/util/dso.c
> >>>>> +++ b/tools/perf/util/dso.c
> >>>>> @@ -32,6 +32,7 @@
> >>>>> #include "string2.h"
> >>>>> #include "vdso.h"
> >>>>> #include "annotate-data.h"
> >>>>> +#include "libdw.h"
> >>>>>
> >>>>> static const char * const debuglink_paths[] = {
> >>>>> "%.0s%s",
> >>>>> @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
> >>>>> auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
> >>>>> dso_cache__free(dso);
> >>>>> dso__free_a2l(dso);
> >>>>> + dso__free_a2l_libdw(dso);
> >>>>> dso__free_symsrc_filename(dso);
> >>>>> nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
> >>>>> mutex_destroy(dso__lock(dso));
> >>>>> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> >>>>> index f8ccb9816b89..4aee23775054 100644
> >>>>> --- a/tools/perf/util/dso.h
> >>>>> +++ b/tools/perf/util/dso.h
> >>>>> @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
> >>>>> const char *short_name;
> >>>>> const char *long_name;
> >>>>> void *a2l;
> >>>>> + void *a2l_libdw;
> >>>>> char *symsrc_filename;
> >>>>> #if defined(__powerpc__)
> >>>>> void *dwfl; /* DWARF debug info */
> >>>>> @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
> >>>>> RC_CHK_ACCESS(dso)->a2l = val;
> >>>>> }
> >>>>>
> >>>>> +static inline void *dso__a2l_libdw(const struct dso *dso)
> >>>>> +{
> >>>>> + return RC_CHK_ACCESS(dso)->a2l_libdw;
> >>>>> +}
> >>>>> +
> >>>>> +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
> >>>>> +{
> >>>>> + RC_CHK_ACCESS(dso)->a2l_libdw = val;
> >>>>> +}
> >>>>> +
> >>>>> static inline unsigned int dso__a2l_fails(const struct dso *dso)
> >>>>> {
> >>>>> return RC_CHK_ACCESS(dso)->a2l_fails;
> >>>>> diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
> >>>>> new file mode 100644
> >>>>> index 000000000000..c4331fa8e1a3
> >>>>> --- /dev/null
> >>>>> +++ b/tools/perf/util/libdw.c
> >>>>> @@ -0,0 +1,136 @@
> >>>>> +// SPDX-License-Identifier: GPL-2.0
> >>>>> +#include "dso.h"
> >>>>> +#include "libdw.h"
> >>>>> +#include "srcline.h"
> >>>>> +#include "symbol.h"
> >>>>> +#include "dwarf-aux.h"
> >>>>> +#include <fcntl.h>
> >>>>> +#include <unistd.h>
> >>>>> +#include <elfutils/libdwfl.h>
> >>>>> +
> >>>>> +void dso__free_a2l_libdw(struct dso *dso)
> >>>>> +{
> >>>>> + Dwfl *dwfl = dso__a2l_libdw(dso);
> >>>>> +
> >>>>> + if (dwfl) {
> >>>>> + dwfl_end(dwfl);
> >>>>> + dso__set_a2l_libdw(dso, NULL);
> >>>>> + }
> >>>>> +}
> >>>>> +
> >>>>> +int libdw__addr2line(const char *dso_name, u64 addr,
> >>>>> + char **file, unsigned int *line_nr,
> >>>>> + struct dso *dso, bool unwind_inlines,
> >>>>> + struct inline_node *node, struct symbol *sym)
> >>>>> +{
> >>>>> + static const Dwfl_Callbacks offline_callbacks = {
> >>>>> + .find_debuginfo = dwfl_standard_find_debuginfo,
> >>>>> + .section_address = dwfl_offline_section_address,
> >>>>> + .find_elf = dwfl_build_id_find_elf,
> >>>>> + };
> >>>>> + Dwfl *dwfl = dso__a2l_libdw(dso);
> >>>>> + Dwfl_Module *mod;
> >>>>> + Dwfl_Line *dwline;
> >>>>> + Dwarf_Addr bias;
> >>>>> + const char *src;
> >>>>> + int lineno;
> >>>>> +
> >>>>> + if (!dwfl) {
> >>>>> + /*
> >>>>> + * Initialize Dwfl session.
> >>>>> + * We need to open the DSO file to report it to libdw.
> >>>>> + */
> >>>>> + int fd;
> >>>>> +
> >>>>> + fd = open(dso_name, O_RDONLY);
> >>>>> + if (fd < 0)
> >>>>> + return 0;
> >>>>> +
> >>>>> + dwfl = dwfl_begin(&offline_callbacks);
> >>>>> + if (!dwfl) {
> >>>>> + close(fd);
> >>>>> + return 0;
> >>>>> + }
> >>>>> +
> >>>>> + /*
> >>>>> + * If the report is successful, the file descriptor fd is consumed
> >>>>> + * and closed by the Dwfl. If not, it is not closed.
> >>>>> + */
> >>>>> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> >>>>> + if (!mod) {
> >>>>> + dwfl_end(dwfl);
> >>>>> + close(fd);
> >>>>> + return 0;
> >>>>> + }
> >>>>> +
> >>>>> + dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
> >>>>> + dso__set_a2l_libdw(dso, dwfl);
> >>>>> + } else {
> >>>>> + /* Dwfl session already initialized, get module for address. */
> >>>>> + mod = dwfl_addrmodule(dwfl, addr);
> >>>>> + }
> >>>>> +
> >>>>> + if (!mod)
> >>>>> + return 0;
> >>>>> +
> >>>>> + /* Find source line information for the address. */
> >>>>> + dwline = dwfl_module_getsrc(mod, addr);
> >>>>> + if (!dwline)
> >>>>> + return 0;
> >>>>> +
> >>>>> + /* Get line information. */
> >>>>> + src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
> >>>>> +
> >>>>> + if (file)
> >>>>> + *file = src ? strdup(src) : NULL;
> >>>>> + if (line_nr)
> >>>>> + *line_nr = lineno;
> >>>>> +
> >>>>> + /* Optionally unwind inline function call chain. */
> >>>>> + if (unwind_inlines && node && src) {
> >>>>> + Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
> >>>>> + Dwarf_Die *scopes = NULL;
> >>>>> + int nscopes;
> >>>>> +
> >>>>> + if (!cudie)
> >>>>> + return 1;
> >>>>> +
> >>>>> + nscopes = die_get_scopes(cudie, addr, &scopes);
> >>>>> + if (nscopes > 0) {
> >>>>> + int i;
> >>>>> + const char *call_file = src;
> >>>>> + unsigned int call_line = lineno;
> >>>>> +
> >>>>> + for (i = 0; i < nscopes; i++) {
> >>>>> + Dwarf_Die *die = &scopes[i];
> >>>>> + struct symbol *inline_sym;
> >>>>> + char *srcline = NULL;
> >>>>> + int tag = dwarf_tag(die);
> >>>>> +
> >>>>> + /* We are interested in inlined subroutines. */
> >>>>> + if (tag != DW_TAG_inlined_subroutine &&
> >>>>> + tag != DW_TAG_subprogram)
> >>>>> + continue;
> >>>>> +
> >>>>> + inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
> >>>>> +
> >>>>> + if (call_file)
> >>>>> + srcline = srcline_from_fileline(call_file, call_line);
> >>>>> +
> >>>>> + inline_list__append(inline_sym, srcline, node);
> >>>>> +
> >>>>> + /* Update call site for next level. */
> >>>>> + if (tag == DW_TAG_inlined_subroutine) {
> >>>>> + call_file = die_get_call_file(die);
> >>>>> + call_line = die_get_call_lineno(die);
> >>>>> + } else {
> >>>>> + /* Reached the root subprogram. */
> >>>>> + break;
> >>>>> + }
> >>>>> + }
> >>>>> + free(scopes);
> >>>>> + }
> >>>>> + }
> >>>>> +
> >>>>> + return 1;
> >>>>> +}
> >>>>> diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
> >>>>> new file mode 100644
> >>>>> index 000000000000..0f8d7b4a11a5
> >>>>> --- /dev/null
> >>>>> +++ b/tools/perf/util/libdw.h
> >>>>> @@ -0,0 +1,60 @@
> >>>>> +/* SPDX-License-Identifier: GPL-2.0 */
> >>>>> +#ifndef PERF_LIBDW_H
> >>>>> +#define PERF_LIBDW_H
> >>>>> +
> >>>>> +#include <linux/types.h>
> >>>>> +
> >>>>> +struct dso;
> >>>>> +struct inline_node;
> >>>>> +struct symbol;
> >>>>> +
> >>>>> +#ifdef HAVE_LIBDW_SUPPORT
> >>>>> +/*
> >>>>> + * libdw__addr2line - Convert address to source location using libdw
> >>>>> + * @dso_name: Name of the DSO
> >>>>> + * @addr: Address to resolve
> >>>>> + * @file: Pointer to return filename (caller must free)
> >>>>> + * @line_nr: Pointer to return line number
> >>>>> + * @dso: The dso struct
> >>>>> + * @unwind_inlines: Whether to unwind inline function calls
> >>>>> + * @node: Inline node list to append to
> >>>>> + * @sym: The symbol associated with the address
> >>>>> + *
> >>>>> + * This function initializes a Dwfl context for the DSO if not already present,
> >>>>> + * finds the source line information for the given address, and optionally
> >>>>> + * resolves inline function call chains.
> >>>>> + *
> >>>>> + * Returns 1 on success (found), 0 on failure (not found).
> >>>>> + */
> >>>>> +int libdw__addr2line(const char *dso_name, u64 addr, char **file,
> >>>>> + unsigned int *line_nr, struct dso *dso,
> >>>>> + bool unwind_inlines, struct inline_node *node,
> >>>>> + struct symbol *sym);
> >>>>> +
> >>>>> +/*
> >>>>> + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
> >>>>> + * @dso: The dso to free resources for
> >>>>> + *
> >>>>> + * This function cleans up the Dwfl context used for addr2line lookups.
> >>>>> + */
> >>>>> +void dso__free_a2l_libdw(struct dso *dso);
> >>>>> +
> >>>>> +#else /* HAVE_LIBDW_SUPPORT */
> >>>>> +
> >>>>> +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
> >>>>> + u64 addr __maybe_unused, char **file __maybe_unused,
> >>>>> + unsigned int *line_nr __maybe_unused,
> >>>>> + struct dso *dso __maybe_unused,
> >>>>> + bool unwind_inlines __maybe_unused,
> >>>>> + struct inline_node *node __maybe_unused,
> >>>>> + struct symbol *sym __maybe_unused)
> >>>>> +{
> >>>>> + return 0;
> >>>>> +}
> >>>>> +
> >>>>> +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
> >>>>> +{
> >>>>> +}
> >>>>> +#endif /* HAVE_LIBDW_SUPPORT */
> >>>>> +
> >>>>> +#endif /* PERF_LIBDW_H */
> >>>>> diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
> >>>>> index 27c0966611ab..4b456c4d4138 100644
> >>>>> --- a/tools/perf/util/srcline.c
> >>>>> +++ b/tools/perf/util/srcline.c
> >>>>> @@ -6,6 +6,7 @@
> >>>>> #include "libbfd.h"
> >>>>> #include "llvm.h"
> >>>>> #include "symbol.h"
> >>>>> +#include "libdw.h"
> >>>>>
> >>>>> #include <inttypes.h>
> >>>>> #include <string.h>
> >>>>> @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
> >>>>> {
> >>>>> int ret;
> >>>>>
> >>>>> + ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> >>>>> + if (ret > 0)
> >>>>> + return ret;
> >>>>> +
> >>>>> ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> >>>>> if (ret > 0)
> >>>>> return ret;
> >>>>> --
> >>>>> 2.52.0.rc2.455.g230fcf2819-goog
> >>>>>
> >>
>
On 28/11/2025 9:00 am, Ian Rogers wrote:
> On Thu, Nov 27, 2025 at 5:48 AM James Clark <james.clark@linaro.org> wrote:
>>
>>
>>
>> On 27/11/2025 1:19 pm, Ian Rogers wrote:
>>> On Thu, Nov 27, 2025 at 4:16 AM James Clark <james.clark@linaro.org> wrote:
>>>>
>>>>
>>>>
>>>> On 27/11/2025 11:43 am, Ian Rogers wrote:
>>>>> On Wed, Nov 26, 2025 at 10:27 AM Namhyung Kim <namhyung@kernel.org> wrote:
>>>>>>
>>>>>> On Sat, Nov 22, 2025 at 01:39:34AM -0800, Ian Rogers wrote:
>>>>>>> Add an implementation of addr2line that uses libdw. Other addr2line
>>>>>>> implementations or, in the case of forking addr2line, slow. Add an
>>>>>>> implementation that caches the libdw information in the dso and uses
>>>>>>> it to find the file and line number information.
>>>>>
>>>>> Thanks James and Namhyung for the reviews! I agree with James' comment
>>>>> about a typo in the commit message.
>>>>>
>>>>>> My concern is the limit in the open file descriptors in case the data
>>>>>> touched a lot of different libraries. The DSO code has some logic to
>>>>>> deal with it but I'm not sure if we can share that since libdw seems to
>>>>>> want to own the FD.
>>>>>
>>>>> The code opens the FD:
>>>>>
>>>>> + fd = open(dso_name, O_RDONLY);
>>>>> + if (fd < 0)
>>>>> + return 0;
>>>>> +
>>>>> + dwfl = dwfl_begin(&offline_callbacks);
>>>>> + if (!dwfl) {
>>>>> + close(fd);
>>>>> + return 0;
>>>>> + }
>>>>>
>>>>> It then uses the FD and closes it (the close is hidden in libdw itself):
>>>>>
>>>>> + /*
>>>>> + * If the report is successful, the file descriptor fd
>>>>> is consumed
>>>>> + * and closed by the Dwfl. If not, it is not closed.
>>>>> + */
>>>>> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
>>>>>
>>>>> So it is possible we exhaust all the file descriptors if there are
>>>>> multiple concurrent calls to libdw__addr2line and every dso has
>>>>> missing libdw dwfl data... but because the open/close are close
>>>>> together and that 1 FD is say small to the FDs needed for the
>>>>> cmd__addr2line, I don't think it is a problem we need to specifically
>>>>> handle. Were the FD kept open until the dso was deleted, I'd agree
>>>>> with you.
>>>>>
>>>>>> Also, have you checked if this generates the exactly same output with
>>>>>> other implementations?
>>>>>
>>>>> So the code passes `perf test` and I was checking functionality with
>>>>> perf annotate, top, etc. What I saw looked good, but it may not have
>>>>> been exhaustive. I didn't specifically create a test that compares the
>>>>> output of the different addr2line implementations. Such a test would
>>>>> be possible, it's not something we've done elsewhere.
>>>>>
>>>>> Thanks,
>>>>> Ian
>>>>>
>>>>
>>>> I manually looked at a couple of line numbers and they looked
>>>> reasonable. I think an automated test that compared dwarf decoders would
>>>> be a bit of a nightmare because I'm sure there would always be subtle
>>>> differences.
>>>>
>>>> Doing a manual side by side comparison of libdw__addr2line() and
>>>> llvm__addr2line(), they seem to be quite different:
>>>>
>>>> $ perf record -- perf test -w leafloop
>>>> $ perf script -F ip,srcline > libdw_addr2line.txt
>>>> # Comment out libdw_addr2line() and rebuild
>>>> $ perf script -F ip,srcline > llvm_addr2line.txt
>>>> $ diff libdw_addr2line.txt llvm_addr2line.txt
>>>>
>>>> It gets all of the simple leafloop workload lines the same, but lots of
>>>> the libc stuff is different.
>>>>
>>>> For example libdw gives cpu-features.c:350 where llvm gives strcmp.S. At
>>>> least that one looks like inlining so llvm might be "better", but where
>>>> it gives dl-cache.c:490 isntead of llvm's mmap64.c:47, it's hard to see
>>>> how that can be inlining if they're in different compilation units.
>>>>
>>>> If the llvm addr2line implementation is also supposed to be slow, it
>>>> just means we're trading speed with accuracy with this change. Hard to
>>>> say what the default should be in that case.
>>>
>>> Agreed. We could do some kind of option scheme like with the disassemblers:
>>> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/disasm.c?h=perf-tools-next#n1715
>>>
>>> I'm not sure there are currently any distributions using the LLVM
>>> options, this in part motivates:
>>> https://lore.kernel.org/lkml/20251007163835.3152881-1-irogers@google.com/
>>> but the addr2line APIs are a pain there - see the extra generated .so.
>>> Because of that it could be reasonable to delete the LLVM addr2line
>>> code and just focus on libdw. I kind of wish we could also delete the
>>> precarious command forking versions too. And libbfd... Perhaps with
>>> this code, those advocating libbfd have a fast enough alternative
>>> without bringing in large dependencies like libLLVM.
>>>
>>> Thanks,
>>> Ian
>>>
>>
>> Personally for debugging I would want the most accurate and detailed
>> information possible and don't care at all about the size of
>> dependencies. If Perf is a tool for debugging then surely that should be
>> the default? But right now I don't actually know which of the outputs is
>> most accurate although I'll assume that the llvm one is.
>
> I know LLVM got dwarf 5 support early. I'm not sure if accurate is the
> best word to compare libdw and LLVM as, if libdw supports the format,
> discrepancies are bugs in LLVM or libdw, .. Building around LLVM as a
> common base sgtm and my main use-case doesn't get impeded by the large
> dependency because of the dlopen patches. As libelf/libdw is pretty
> much a given for a perf build, as it is required for libbpf, then the
> code here can avoid the fork/exec fallback. I can see the sense in
> trying with LLVM first and then falling back to libdw.
>
Seems like my libc does have dwarf 5 symbols. Looking a bit more I still
think "accurate" is the right word. Comparing gdb, forked addr2line and
llvm_addr2line(), all 3 agree on the source line for every address in my
recording. The only one that disagrees is libdw_addr2line(). I don't
know if there's an issue with how it's being called, or there is a bug
in the library.
Digging even deeper, if I put breakpoints on the lines that
libdw_addr2line() gives, they aren't even hit. So it's not even like
it's not de-inlining stuff, which you could argue is fine. And there is
the issue that some of the results are in completely different C files.
It's hard to see why it's giving such different results without
debugging libdw line by line.
I'm not sure if you see the same thing with a simple recording or you
want me to send a perf archive?
>> Wanting the smallest application possible while trading away detail and
>> accuracy seems like an unusual special case that should be opt in. It
>> also seems to relate to this old discussion [1], in that if we're going
>> to keep the llvm depencency then it doesn't make sense to re-write
>> anything in Perf.
>
> So I think PE support in libdw wouldn't be a priority and so LLVM for
> the win there. I think distributions have been slow to pick up the
> LLVM dependency, I'm not sure what the issue is there. It would be
> nice to start removing some of the alternatives the perf build
> supports. The libbfd and libunwind code is only built with specific
> opt-ins, and I think the fork/exec addr2line is redundant after this
> change. For addr2line that'd bring the 2 implementations down to libdw
It might be a bit premature to drop the addr2line fork if libdw isn't
mature enough. Especially as it seems to fall over on such a basic test.
Hopefully it's just an issue with how it's called or the version that I
have.
> and LLVM. As the recent libbfd fixes show [1], inadvertently we can
> break these largely untested dependencies by exposing latent bugs in
> things like improper initialization.
>
> Thanks,
> Ian
>
> [1] https://lore.kernel.org/lkml/20251112074311.1440101-1-irogers@google.com/
>
>> [1]:
>> https://lore.kernel.org/linux-perf-users/549d3812-a606-4981-83f5-0a99b0ff9f6a@linaro.org/
>>
>>>>>> Thanks,
>>>>>> Namhyung
>>>>>>
>>>>>>>
>>>>>>> Signed-off-by: Ian Rogers <irogers@google.com>
>>>>>>> ---
>>>>>>> tools/perf/util/Build | 1 +
>>>>>>> tools/perf/util/dso.c | 2 +
>>>>>>> tools/perf/util/dso.h | 11 +++
>>>>>>> tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
>>>>>>> tools/perf/util/libdw.h | 60 +++++++++++++++++
>>>>>>> tools/perf/util/srcline.c | 5 ++
>>>>>>> 6 files changed, 215 insertions(+)
>>>>>>> create mode 100644 tools/perf/util/libdw.c
>>>>>>> create mode 100644 tools/perf/util/libdw.h
>>>>>>>
>>>>>>> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
>>>>>>> index 1c2a43e1dc68..2bed6274e248 100644
>>>>>>> --- a/tools/perf/util/Build
>>>>>>> +++ b/tools/perf/util/Build
>>>>>>> @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
>>>>>>> perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
>>>>>>> perf-util-$(CONFIG_LIBDW) += debuginfo.o
>>>>>>> perf-util-$(CONFIG_LIBDW) += annotate-data.o
>>>>>>> +perf-util-$(CONFIG_LIBDW) += libdw.o
>>>>>>>
>>>>>>> perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
>>>>>>> perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
>>>>>>> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
>>>>>>> index 344e689567ee..06980844c014 100644
>>>>>>> --- a/tools/perf/util/dso.c
>>>>>>> +++ b/tools/perf/util/dso.c
>>>>>>> @@ -32,6 +32,7 @@
>>>>>>> #include "string2.h"
>>>>>>> #include "vdso.h"
>>>>>>> #include "annotate-data.h"
>>>>>>> +#include "libdw.h"
>>>>>>>
>>>>>>> static const char * const debuglink_paths[] = {
>>>>>>> "%.0s%s",
>>>>>>> @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
>>>>>>> auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
>>>>>>> dso_cache__free(dso);
>>>>>>> dso__free_a2l(dso);
>>>>>>> + dso__free_a2l_libdw(dso);
>>>>>>> dso__free_symsrc_filename(dso);
>>>>>>> nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
>>>>>>> mutex_destroy(dso__lock(dso));
>>>>>>> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
>>>>>>> index f8ccb9816b89..4aee23775054 100644
>>>>>>> --- a/tools/perf/util/dso.h
>>>>>>> +++ b/tools/perf/util/dso.h
>>>>>>> @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
>>>>>>> const char *short_name;
>>>>>>> const char *long_name;
>>>>>>> void *a2l;
>>>>>>> + void *a2l_libdw;
>>>>>>> char *symsrc_filename;
>>>>>>> #if defined(__powerpc__)
>>>>>>> void *dwfl; /* DWARF debug info */
>>>>>>> @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
>>>>>>> RC_CHK_ACCESS(dso)->a2l = val;
>>>>>>> }
>>>>>>>
>>>>>>> +static inline void *dso__a2l_libdw(const struct dso *dso)
>>>>>>> +{
>>>>>>> + return RC_CHK_ACCESS(dso)->a2l_libdw;
>>>>>>> +}
>>>>>>> +
>>>>>>> +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
>>>>>>> +{
>>>>>>> + RC_CHK_ACCESS(dso)->a2l_libdw = val;
>>>>>>> +}
>>>>>>> +
>>>>>>> static inline unsigned int dso__a2l_fails(const struct dso *dso)
>>>>>>> {
>>>>>>> return RC_CHK_ACCESS(dso)->a2l_fails;
>>>>>>> diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
>>>>>>> new file mode 100644
>>>>>>> index 000000000000..c4331fa8e1a3
>>>>>>> --- /dev/null
>>>>>>> +++ b/tools/perf/util/libdw.c
>>>>>>> @@ -0,0 +1,136 @@
>>>>>>> +// SPDX-License-Identifier: GPL-2.0
>>>>>>> +#include "dso.h"
>>>>>>> +#include "libdw.h"
>>>>>>> +#include "srcline.h"
>>>>>>> +#include "symbol.h"
>>>>>>> +#include "dwarf-aux.h"
>>>>>>> +#include <fcntl.h>
>>>>>>> +#include <unistd.h>
>>>>>>> +#include <elfutils/libdwfl.h>
>>>>>>> +
>>>>>>> +void dso__free_a2l_libdw(struct dso *dso)
>>>>>>> +{
>>>>>>> + Dwfl *dwfl = dso__a2l_libdw(dso);
>>>>>>> +
>>>>>>> + if (dwfl) {
>>>>>>> + dwfl_end(dwfl);
>>>>>>> + dso__set_a2l_libdw(dso, NULL);
>>>>>>> + }
>>>>>>> +}
>>>>>>> +
>>>>>>> +int libdw__addr2line(const char *dso_name, u64 addr,
>>>>>>> + char **file, unsigned int *line_nr,
>>>>>>> + struct dso *dso, bool unwind_inlines,
>>>>>>> + struct inline_node *node, struct symbol *sym)
>>>>>>> +{
>>>>>>> + static const Dwfl_Callbacks offline_callbacks = {
>>>>>>> + .find_debuginfo = dwfl_standard_find_debuginfo,
>>>>>>> + .section_address = dwfl_offline_section_address,
>>>>>>> + .find_elf = dwfl_build_id_find_elf,
>>>>>>> + };
>>>>>>> + Dwfl *dwfl = dso__a2l_libdw(dso);
>>>>>>> + Dwfl_Module *mod;
>>>>>>> + Dwfl_Line *dwline;
>>>>>>> + Dwarf_Addr bias;
>>>>>>> + const char *src;
>>>>>>> + int lineno;
>>>>>>> +
>>>>>>> + if (!dwfl) {
>>>>>>> + /*
>>>>>>> + * Initialize Dwfl session.
>>>>>>> + * We need to open the DSO file to report it to libdw.
>>>>>>> + */
>>>>>>> + int fd;
>>>>>>> +
>>>>>>> + fd = open(dso_name, O_RDONLY);
>>>>>>> + if (fd < 0)
>>>>>>> + return 0;
>>>>>>> +
>>>>>>> + dwfl = dwfl_begin(&offline_callbacks);
>>>>>>> + if (!dwfl) {
>>>>>>> + close(fd);
>>>>>>> + return 0;
>>>>>>> + }
>>>>>>> +
>>>>>>> + /*
>>>>>>> + * If the report is successful, the file descriptor fd is consumed
>>>>>>> + * and closed by the Dwfl. If not, it is not closed.
>>>>>>> + */
>>>>>>> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
>>>>>>> + if (!mod) {
>>>>>>> + dwfl_end(dwfl);
>>>>>>> + close(fd);
>>>>>>> + return 0;
>>>>>>> + }
>>>>>>> +
>>>>>>> + dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
>>>>>>> + dso__set_a2l_libdw(dso, dwfl);
>>>>>>> + } else {
>>>>>>> + /* Dwfl session already initialized, get module for address. */
>>>>>>> + mod = dwfl_addrmodule(dwfl, addr);
>>>>>>> + }
>>>>>>> +
>>>>>>> + if (!mod)
>>>>>>> + return 0;
>>>>>>> +
>>>>>>> + /* Find source line information for the address. */
>>>>>>> + dwline = dwfl_module_getsrc(mod, addr);
>>>>>>> + if (!dwline)
>>>>>>> + return 0;
>>>>>>> +
>>>>>>> + /* Get line information. */
>>>>>>> + src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
>>>>>>> +
>>>>>>> + if (file)
>>>>>>> + *file = src ? strdup(src) : NULL;
>>>>>>> + if (line_nr)
>>>>>>> + *line_nr = lineno;
>>>>>>> +
>>>>>>> + /* Optionally unwind inline function call chain. */
>>>>>>> + if (unwind_inlines && node && src) {
>>>>>>> + Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
>>>>>>> + Dwarf_Die *scopes = NULL;
>>>>>>> + int nscopes;
>>>>>>> +
>>>>>>> + if (!cudie)
>>>>>>> + return 1;
>>>>>>> +
>>>>>>> + nscopes = die_get_scopes(cudie, addr, &scopes);
>>>>>>> + if (nscopes > 0) {
>>>>>>> + int i;
>>>>>>> + const char *call_file = src;
>>>>>>> + unsigned int call_line = lineno;
>>>>>>> +
>>>>>>> + for (i = 0; i < nscopes; i++) {
>>>>>>> + Dwarf_Die *die = &scopes[i];
>>>>>>> + struct symbol *inline_sym;
>>>>>>> + char *srcline = NULL;
>>>>>>> + int tag = dwarf_tag(die);
>>>>>>> +
>>>>>>> + /* We are interested in inlined subroutines. */
>>>>>>> + if (tag != DW_TAG_inlined_subroutine &&
>>>>>>> + tag != DW_TAG_subprogram)
>>>>>>> + continue;
>>>>>>> +
>>>>>>> + inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
>>>>>>> +
>>>>>>> + if (call_file)
>>>>>>> + srcline = srcline_from_fileline(call_file, call_line);
>>>>>>> +
>>>>>>> + inline_list__append(inline_sym, srcline, node);
>>>>>>> +
>>>>>>> + /* Update call site for next level. */
>>>>>>> + if (tag == DW_TAG_inlined_subroutine) {
>>>>>>> + call_file = die_get_call_file(die);
>>>>>>> + call_line = die_get_call_lineno(die);
>>>>>>> + } else {
>>>>>>> + /* Reached the root subprogram. */
>>>>>>> + break;
>>>>>>> + }
>>>>>>> + }
>>>>>>> + free(scopes);
>>>>>>> + }
>>>>>>> + }
>>>>>>> +
>>>>>>> + return 1;
>>>>>>> +}
>>>>>>> diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
>>>>>>> new file mode 100644
>>>>>>> index 000000000000..0f8d7b4a11a5
>>>>>>> --- /dev/null
>>>>>>> +++ b/tools/perf/util/libdw.h
>>>>>>> @@ -0,0 +1,60 @@
>>>>>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>>>>>> +#ifndef PERF_LIBDW_H
>>>>>>> +#define PERF_LIBDW_H
>>>>>>> +
>>>>>>> +#include <linux/types.h>
>>>>>>> +
>>>>>>> +struct dso;
>>>>>>> +struct inline_node;
>>>>>>> +struct symbol;
>>>>>>> +
>>>>>>> +#ifdef HAVE_LIBDW_SUPPORT
>>>>>>> +/*
>>>>>>> + * libdw__addr2line - Convert address to source location using libdw
>>>>>>> + * @dso_name: Name of the DSO
>>>>>>> + * @addr: Address to resolve
>>>>>>> + * @file: Pointer to return filename (caller must free)
>>>>>>> + * @line_nr: Pointer to return line number
>>>>>>> + * @dso: The dso struct
>>>>>>> + * @unwind_inlines: Whether to unwind inline function calls
>>>>>>> + * @node: Inline node list to append to
>>>>>>> + * @sym: The symbol associated with the address
>>>>>>> + *
>>>>>>> + * This function initializes a Dwfl context for the DSO if not already present,
>>>>>>> + * finds the source line information for the given address, and optionally
>>>>>>> + * resolves inline function call chains.
>>>>>>> + *
>>>>>>> + * Returns 1 on success (found), 0 on failure (not found).
>>>>>>> + */
>>>>>>> +int libdw__addr2line(const char *dso_name, u64 addr, char **file,
>>>>>>> + unsigned int *line_nr, struct dso *dso,
>>>>>>> + bool unwind_inlines, struct inline_node *node,
>>>>>>> + struct symbol *sym);
>>>>>>> +
>>>>>>> +/*
>>>>>>> + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
>>>>>>> + * @dso: The dso to free resources for
>>>>>>> + *
>>>>>>> + * This function cleans up the Dwfl context used for addr2line lookups.
>>>>>>> + */
>>>>>>> +void dso__free_a2l_libdw(struct dso *dso);
>>>>>>> +
>>>>>>> +#else /* HAVE_LIBDW_SUPPORT */
>>>>>>> +
>>>>>>> +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
>>>>>>> + u64 addr __maybe_unused, char **file __maybe_unused,
>>>>>>> + unsigned int *line_nr __maybe_unused,
>>>>>>> + struct dso *dso __maybe_unused,
>>>>>>> + bool unwind_inlines __maybe_unused,
>>>>>>> + struct inline_node *node __maybe_unused,
>>>>>>> + struct symbol *sym __maybe_unused)
>>>>>>> +{
>>>>>>> + return 0;
>>>>>>> +}
>>>>>>> +
>>>>>>> +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
>>>>>>> +{
>>>>>>> +}
>>>>>>> +#endif /* HAVE_LIBDW_SUPPORT */
>>>>>>> +
>>>>>>> +#endif /* PERF_LIBDW_H */
>>>>>>> diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
>>>>>>> index 27c0966611ab..4b456c4d4138 100644
>>>>>>> --- a/tools/perf/util/srcline.c
>>>>>>> +++ b/tools/perf/util/srcline.c
>>>>>>> @@ -6,6 +6,7 @@
>>>>>>> #include "libbfd.h"
>>>>>>> #include "llvm.h"
>>>>>>> #include "symbol.h"
>>>>>>> +#include "libdw.h"
>>>>>>>
>>>>>>> #include <inttypes.h>
>>>>>>> #include <string.h>
>>>>>>> @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
>>>>>>> {
>>>>>>> int ret;
>>>>>>>
>>>>>>> + ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
>>>>>>> + if (ret > 0)
>>>>>>> + return ret;
>>>>>>> +
>>>>>>> ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
>>>>>>> if (ret > 0)
>>>>>>> return ret;
>>>>>>> --
>>>>>>> 2.52.0.rc2.455.g230fcf2819-goog
>>>>>>>
>>>>
>>
On 22/11/2025 9:39 am, Ian Rogers wrote:
> Add an implementation of addr2line that uses libdw. Other addr2line
> implementations or, in the case of forking addr2line, slow. Add an
"are slow"?
Other that that:
Reviewed-by: James Clark <james.clark@linaro.org>
> implementation that caches the libdw information in the dso and uses
> it to find the file and line number information.
>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/util/Build | 1 +
> tools/perf/util/dso.c | 2 +
> tools/perf/util/dso.h | 11 +++
> tools/perf/util/libdw.c | 136 ++++++++++++++++++++++++++++++++++++++
> tools/perf/util/libdw.h | 60 +++++++++++++++++
> tools/perf/util/srcline.c | 5 ++
> 6 files changed, 215 insertions(+)
> create mode 100644 tools/perf/util/libdw.c
> create mode 100644 tools/perf/util/libdw.h
>
> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> index 1c2a43e1dc68..2bed6274e248 100644
> --- a/tools/perf/util/Build
> +++ b/tools/perf/util/Build
> @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
> perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
> perf-util-$(CONFIG_LIBDW) += debuginfo.o
> perf-util-$(CONFIG_LIBDW) += annotate-data.o
> +perf-util-$(CONFIG_LIBDW) += libdw.o
>
> perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
> perf-util-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index 344e689567ee..06980844c014 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -32,6 +32,7 @@
> #include "string2.h"
> #include "vdso.h"
> #include "annotate-data.h"
> +#include "libdw.h"
>
> static const char * const debuglink_paths[] = {
> "%.0s%s",
> @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
> auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
> dso_cache__free(dso);
> dso__free_a2l(dso);
> + dso__free_a2l_libdw(dso);
> dso__free_symsrc_filename(dso);
> nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
> mutex_destroy(dso__lock(dso));
> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> index f8ccb9816b89..4aee23775054 100644
> --- a/tools/perf/util/dso.h
> +++ b/tools/perf/util/dso.h
> @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
> const char *short_name;
> const char *long_name;
> void *a2l;
> + void *a2l_libdw;
> char *symsrc_filename;
> #if defined(__powerpc__)
> void *dwfl; /* DWARF debug info */
> @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
> RC_CHK_ACCESS(dso)->a2l = val;
> }
>
> +static inline void *dso__a2l_libdw(const struct dso *dso)
> +{
> + return RC_CHK_ACCESS(dso)->a2l_libdw;
> +}
> +
> +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
> +{
> + RC_CHK_ACCESS(dso)->a2l_libdw = val;
> +}
> +
> static inline unsigned int dso__a2l_fails(const struct dso *dso)
> {
> return RC_CHK_ACCESS(dso)->a2l_fails;
> diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
> new file mode 100644
> index 000000000000..c4331fa8e1a3
> --- /dev/null
> +++ b/tools/perf/util/libdw.c
> @@ -0,0 +1,136 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "dso.h"
> +#include "libdw.h"
> +#include "srcline.h"
> +#include "symbol.h"
> +#include "dwarf-aux.h"
> +#include <fcntl.h>
> +#include <unistd.h>
> +#include <elfutils/libdwfl.h>
> +
> +void dso__free_a2l_libdw(struct dso *dso)
> +{
> + Dwfl *dwfl = dso__a2l_libdw(dso);
> +
> + if (dwfl) {
> + dwfl_end(dwfl);
> + dso__set_a2l_libdw(dso, NULL);
> + }
> +}
> +
> +int libdw__addr2line(const char *dso_name, u64 addr,
> + char **file, unsigned int *line_nr,
> + struct dso *dso, bool unwind_inlines,
> + struct inline_node *node, struct symbol *sym)
> +{
> + static const Dwfl_Callbacks offline_callbacks = {
> + .find_debuginfo = dwfl_standard_find_debuginfo,
> + .section_address = dwfl_offline_section_address,
> + .find_elf = dwfl_build_id_find_elf,
> + };
> + Dwfl *dwfl = dso__a2l_libdw(dso);
> + Dwfl_Module *mod;
> + Dwfl_Line *dwline;
> + Dwarf_Addr bias;
> + const char *src;
> + int lineno;
> +
> + if (!dwfl) {
> + /*
> + * Initialize Dwfl session.
> + * We need to open the DSO file to report it to libdw.
> + */
> + int fd;
> +
> + fd = open(dso_name, O_RDONLY);
> + if (fd < 0)
> + return 0;
> +
> + dwfl = dwfl_begin(&offline_callbacks);
> + if (!dwfl) {
> + close(fd);
> + return 0;
> + }
> +
> + /*
> + * If the report is successful, the file descriptor fd is consumed
> + * and closed by the Dwfl. If not, it is not closed.
> + */
> + mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> + if (!mod) {
> + dwfl_end(dwfl);
> + close(fd);
> + return 0;
> + }
> +
> + dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
> + dso__set_a2l_libdw(dso, dwfl);
> + } else {
> + /* Dwfl session already initialized, get module for address. */
> + mod = dwfl_addrmodule(dwfl, addr);
> + }
> +
> + if (!mod)
> + return 0;
> +
> + /* Find source line information for the address. */
> + dwline = dwfl_module_getsrc(mod, addr);
> + if (!dwline)
> + return 0;
> +
> + /* Get line information. */
> + src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
> +
> + if (file)
> + *file = src ? strdup(src) : NULL;
> + if (line_nr)
> + *line_nr = lineno;
> +
> + /* Optionally unwind inline function call chain. */
> + if (unwind_inlines && node && src) {
> + Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
> + Dwarf_Die *scopes = NULL;
> + int nscopes;
> +
> + if (!cudie)
> + return 1;
> +
> + nscopes = die_get_scopes(cudie, addr, &scopes);
> + if (nscopes > 0) {
> + int i;
> + const char *call_file = src;
> + unsigned int call_line = lineno;
> +
> + for (i = 0; i < nscopes; i++) {
> + Dwarf_Die *die = &scopes[i];
> + struct symbol *inline_sym;
> + char *srcline = NULL;
> + int tag = dwarf_tag(die);
> +
> + /* We are interested in inlined subroutines. */
> + if (tag != DW_TAG_inlined_subroutine &&
> + tag != DW_TAG_subprogram)
> + continue;
> +
> + inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
> +
> + if (call_file)
> + srcline = srcline_from_fileline(call_file, call_line);
> +
> + inline_list__append(inline_sym, srcline, node);
> +
> + /* Update call site for next level. */
> + if (tag == DW_TAG_inlined_subroutine) {
> + call_file = die_get_call_file(die);
> + call_line = die_get_call_lineno(die);
> + } else {
> + /* Reached the root subprogram. */
> + break;
> + }
> + }
> + free(scopes);
> + }
> + }
> +
> + return 1;
> +}
> diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
> new file mode 100644
> index 000000000000..0f8d7b4a11a5
> --- /dev/null
> +++ b/tools/perf/util/libdw.h
> @@ -0,0 +1,60 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef PERF_LIBDW_H
> +#define PERF_LIBDW_H
> +
> +#include <linux/types.h>
> +
> +struct dso;
> +struct inline_node;
> +struct symbol;
> +
> +#ifdef HAVE_LIBDW_SUPPORT
> +/*
> + * libdw__addr2line - Convert address to source location using libdw
> + * @dso_name: Name of the DSO
> + * @addr: Address to resolve
> + * @file: Pointer to return filename (caller must free)
> + * @line_nr: Pointer to return line number
> + * @dso: The dso struct
> + * @unwind_inlines: Whether to unwind inline function calls
> + * @node: Inline node list to append to
> + * @sym: The symbol associated with the address
> + *
> + * This function initializes a Dwfl context for the DSO if not already present,
> + * finds the source line information for the given address, and optionally
> + * resolves inline function call chains.
> + *
> + * Returns 1 on success (found), 0 on failure (not found).
> + */
> +int libdw__addr2line(const char *dso_name, u64 addr, char **file,
> + unsigned int *line_nr, struct dso *dso,
> + bool unwind_inlines, struct inline_node *node,
> + struct symbol *sym);
> +
> +/*
> + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
> + * @dso: The dso to free resources for
> + *
> + * This function cleans up the Dwfl context used for addr2line lookups.
> + */
> +void dso__free_a2l_libdw(struct dso *dso);
> +
> +#else /* HAVE_LIBDW_SUPPORT */
> +
> +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
> + u64 addr __maybe_unused, char **file __maybe_unused,
> + unsigned int *line_nr __maybe_unused,
> + struct dso *dso __maybe_unused,
> + bool unwind_inlines __maybe_unused,
> + struct inline_node *node __maybe_unused,
> + struct symbol *sym __maybe_unused)
> +{
> + return 0;
> +}
> +
> +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
> +{
> +}
> +#endif /* HAVE_LIBDW_SUPPORT */
> +
> +#endif /* PERF_LIBDW_H */
> diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
> index 27c0966611ab..4b456c4d4138 100644
> --- a/tools/perf/util/srcline.c
> +++ b/tools/perf/util/srcline.c
> @@ -6,6 +6,7 @@
> #include "libbfd.h"
> #include "llvm.h"
> #include "symbol.h"
> +#include "libdw.h"
>
> #include <inttypes.h>
> #include <string.h>
> @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
> {
> int ret;
>
> + ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> + if (ret > 0)
> + return ret;
> +
> ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> if (ret > 0)
> return ret;
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