This patch enables dumping kfunc prototypes from bpftool. This is useful
b/c with this patch, end users will no longer have to manually define
kfunc prototypes. For the kernel tree, this also means we can drop
kfunc prototypes from:
tools/testing/selftests/bpf/bpf_kfuncs.h
tools/testing/selftests/bpf/bpf_experimental.h
Example usage:
$ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux
$ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;
Note that this patch is only effective after the enabling pahole [0]
change is merged and the resulting feature enabled with
--btf_features=decl_tag_kfuncs.
[0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
---
tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)
diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 91fcb75babe3..0fd78a476286 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -20,6 +20,8 @@
#include "json_writer.h"
#include "main.h"
+#define KFUNC_DECL_TAG "bpf_kfunc"
+
static const char * const btf_kind_str[NR_BTF_KINDS] = {
[BTF_KIND_UNKN] = "UNKNOWN",
[BTF_KIND_INT] = "INT",
@@ -454,6 +456,39 @@ static int dump_btf_raw(const struct btf *btf,
return 0;
}
+static int dump_btf_kfuncs(struct btf_dump *d, const struct btf *btf)
+{
+ DECLARE_LIBBPF_OPTS(btf_dump_emit_type_decl_opts, opts);
+ int cnt = btf__type_cnt(btf);
+ int i;
+
+ for (i = 1; i < cnt; i++) {
+ const struct btf_type *t = btf__type_by_id(btf, i);
+ const struct btf_type *kft;
+ const char *name;
+ int err;
+
+ if (!btf_is_decl_tag(t))
+ continue;
+
+ name = btf__name_by_offset(btf, t->name_off);
+ if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG)))
+ continue;
+
+ printf("extern ");
+
+ kft = btf__type_by_id(btf, t->type);
+ opts.field_name = btf__name_by_offset(btf, kft->name_off);
+ err = btf_dump__emit_type_decl(d, kft->type, &opts);
+ if (err)
+ return err;
+
+ printf(" __weak __ksym;\n\n");
+ }
+
+ return 0;
+}
+
static void __printf(2, 0) btf_dump_printf(void *ctx,
const char *fmt, va_list args)
{
@@ -476,6 +511,12 @@ static int dump_btf_c(const struct btf *btf,
printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n");
printf("#endif\n\n");
+ printf("#ifndef __ksym\n");
+ printf("#define __ksym __attribute__((section(\".ksyms\")))\n");
+ printf("#endif\n\n");
+ printf("#ifndef __weak\n");
+ printf("#define __weak __attribute__((weak))\n");
+ printf("#endif\n\n");
if (root_type_cnt) {
for (i = 0; i < root_type_cnt; i++) {
@@ -491,6 +532,10 @@ static int dump_btf_c(const struct btf *btf,
if (err)
goto done;
}
+
+ err = dump_btf_kfuncs(d, btf);
+ if (err)
+ goto done;
}
printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
--
2.42.1On Sun, Feb 4, 2024 at 1:07 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
>
> This patch enables dumping kfunc prototypes from bpftool. This is useful
> b/c with this patch, end users will no longer have to manually define
> kfunc prototypes. For the kernel tree, this also means we can drop
> kfunc prototypes from:
>
> tools/testing/selftests/bpf/bpf_kfuncs.h
> tools/testing/selftests/bpf/bpf_experimental.h
>
> Example usage:
>
> $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux
>
> $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
> extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
> extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
> extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;
>
> Note that this patch is only effective after the enabling pahole [0]
> change is merged and the resulting feature enabled with
> --btf_features=decl_tag_kfuncs.
>
> [0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/
>
> Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
> ---
> tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 45 insertions(+)
>
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 91fcb75babe3..0fd78a476286 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -20,6 +20,8 @@
> #include "json_writer.h"
> #include "main.h"
>
> +#define KFUNC_DECL_TAG "bpf_kfunc"
> +
> static const char * const btf_kind_str[NR_BTF_KINDS] = {
> [BTF_KIND_UNKN] = "UNKNOWN",
> [BTF_KIND_INT] = "INT",
> @@ -454,6 +456,39 @@ static int dump_btf_raw(const struct btf *btf,
> return 0;
> }
>
> +static int dump_btf_kfuncs(struct btf_dump *d, const struct btf *btf)
> +{
> + DECLARE_LIBBPF_OPTS(btf_dump_emit_type_decl_opts, opts);
nit: use shorter LIBBPF_OPTS, DECLARE_LIBBPF_OPTS is a "deprecated"
macro name I hid, but didn't remove
> + int cnt = btf__type_cnt(btf);
> + int i;
> +
> + for (i = 1; i < cnt; i++) {
> + const struct btf_type *t = btf__type_by_id(btf, i);
> + const struct btf_type *kft;
> + const char *name;
> + int err;
> +
> + if (!btf_is_decl_tag(t))
> + continue;
> +
> + name = btf__name_by_offset(btf, t->name_off);
> + if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG)))
> + continue;
should we do a bit more sanity checking here? Check that component_idx
= -1 (entire func) and pointee type is FUNC?
> +
> + printf("extern ");
> +
> + kft = btf__type_by_id(btf, t->type);
nit: reuse t?
> + opts.field_name = btf__name_by_offset(btf, kft->name_off);
> + err = btf_dump__emit_type_decl(d, kft->type, &opts);
> + if (err)
> + return err;
> +
> + printf(" __weak __ksym;\n\n");
why extra endline?
though I'd ensure two empty lines before the first kfunc declaration
to visually separate it from other type. Maybe even add a comment like
`/* BPF kfuncs */` or something like that?
> + }
> +
> + return 0;
> +}
> +
> static void __printf(2, 0) btf_dump_printf(void *ctx,
> const char *fmt, va_list args)
> {
> @@ -476,6 +511,12 @@ static int dump_btf_c(const struct btf *btf,
> printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
> printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n");
> printf("#endif\n\n");
> + printf("#ifndef __ksym\n");
> + printf("#define __ksym __attribute__((section(\".ksyms\")))\n");
> + printf("#endif\n\n");
> + printf("#ifndef __weak\n");
> + printf("#define __weak __attribute__((weak))\n");
> + printf("#endif\n\n");
>
> if (root_type_cnt) {
> for (i = 0; i < root_type_cnt; i++) {
> @@ -491,6 +532,10 @@ static int dump_btf_c(const struct btf *btf,
> if (err)
> goto done;
> }
> +
> + err = dump_btf_kfuncs(d, btf);
> + if (err)
> + goto done;
> }
>
> printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
> --
> 2.42.1
>
Hi Andrii,
On Wed, Feb 07, 2024 at 04:50:15PM -0800, Andrii Nakryiko wrote:
> On Sun, Feb 4, 2024 at 1:07 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
> >
> > This patch enables dumping kfunc prototypes from bpftool. This is useful
> > b/c with this patch, end users will no longer have to manually define
> > kfunc prototypes. For the kernel tree, this also means we can drop
> > kfunc prototypes from:
> >
> > tools/testing/selftests/bpf/bpf_kfuncs.h
> > tools/testing/selftests/bpf/bpf_experimental.h
> >
> > Example usage:
> >
> > $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux
> >
> > $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
> > extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
> > extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
> > extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;
> >
> > Note that this patch is only effective after the enabling pahole [0]
> > change is merged and the resulting feature enabled with
> > --btf_features=decl_tag_kfuncs.
> >
> > [0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/
> >
> > Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
> > ---
> > tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 45 insertions(+)
> >
> > diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> > index 91fcb75babe3..0fd78a476286 100644
> > --- a/tools/bpf/bpftool/btf.c
> > +++ b/tools/bpf/bpftool/btf.c
> > @@ -20,6 +20,8 @@
> > #include "json_writer.h"
> > #include "main.h"
> >
> > +#define KFUNC_DECL_TAG "bpf_kfunc"
> > +
> > static const char * const btf_kind_str[NR_BTF_KINDS] = {
> > [BTF_KIND_UNKN] = "UNKNOWN",
> > [BTF_KIND_INT] = "INT",
> > @@ -454,6 +456,39 @@ static int dump_btf_raw(const struct btf *btf,
> > return 0;
> > }
> >
> > +static int dump_btf_kfuncs(struct btf_dump *d, const struct btf *btf)
> > +{
> > + DECLARE_LIBBPF_OPTS(btf_dump_emit_type_decl_opts, opts);
>
> nit: use shorter LIBBPF_OPTS, DECLARE_LIBBPF_OPTS is a "deprecated"
> macro name I hid, but didn't remove
Ack.
>
> > + int cnt = btf__type_cnt(btf);
> > + int i;
> > +
> > + for (i = 1; i < cnt; i++) {
> > + const struct btf_type *t = btf__type_by_id(btf, i);
> > + const struct btf_type *kft;
> > + const char *name;
> > + int err;
> > +
> > + if (!btf_is_decl_tag(t))
> > + continue;
> > +
> > + name = btf__name_by_offset(btf, t->name_off);
> > + if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG)))
> > + continue;
>
> should we do a bit more sanity checking here? Check that component_idx
> = -1 (entire func) and pointee type is FUNC?
Makes sense. Will add.
>
> > +
> > + printf("extern ");
> > +
> > + kft = btf__type_by_id(btf, t->type);
>
> nit: reuse t?
>
> > + opts.field_name = btf__name_by_offset(btf, kft->name_off);
> > + err = btf_dump__emit_type_decl(d, kft->type, &opts);
> > + if (err)
> > + return err;
> > +
> > + printf(" __weak __ksym;\n\n");
>
> why extra endline?
Was thinking b/c other entities (structs) are double newline separated
that we should keep it up for kfunc prototypes. No opinion -- I'll
change it.
>
> though I'd ensure two empty lines before the first kfunc declaration
> to visually separate it from other type. Maybe even add a comment like
> `/* BPF kfuncs */` or something like that?
Ack.
>
> > + }
> > +
> > + return 0;
> > +}
> > +
> > static void __printf(2, 0) btf_dump_printf(void *ctx,
> > const char *fmt, va_list args)
> > {
> > @@ -476,6 +511,12 @@ static int dump_btf_c(const struct btf *btf,
> > printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
> > printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n");
> > printf("#endif\n\n");
> > + printf("#ifndef __ksym\n");
> > + printf("#define __ksym __attribute__((section(\".ksyms\")))\n");
> > + printf("#endif\n\n");
> > + printf("#ifndef __weak\n");
> > + printf("#define __weak __attribute__((weak))\n");
> > + printf("#endif\n\n");
> >
> > if (root_type_cnt) {
> > for (i = 0; i < root_type_cnt; i++) {
> > @@ -491,6 +532,10 @@ static int dump_btf_c(const struct btf *btf,
> > if (err)
> > goto done;
> > }
> > +
> > + err = dump_btf_kfuncs(d, btf);
> > + if (err)
> > + goto done;
> > }
> >
> > printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
> > --
> > 2.42.1
> >
I'll send the next rev after the pahole changes get merged.
Thanks,
Daniel
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