From: Josh Poimboeuf <jpoimboe@kernel.org>
Add optional support for user space compat mode frame pointer unwinding.
If supported, the arch needs to enable CONFIG_HAVE_UNWIND_USER_COMPAT_FP
and define ARCH_INIT_USER_COMPAT_FP_FRAME.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Co-developed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v9: https://lore.kernel.org/linux-trace-kernel/20250513223551.459986355@goodmis.org/
As asm-generic headers are not included when an architecture defines the
header, having more than one #ifndef and setting variables does not work
with those checks in the asm-generic header and the architecture header
does not define all the values.
- Move #indef arch_unwind_user_state to linux/user_unwind_types.h
- Move the following to linux/unwind_user.h:
#ifndef ARCH_INIT_USER_COMPAT_FP_FRAME
#ifndef arch_unwind_user_init
#ifndef arch_unwind_user_next
- Changed UNWIND_GET_USER_LONG() to use "unsigned long" instead of u64 as
this can be called on 32 bit architectures and just because
"compat_state()" returns false doesn't mean that the value is 64 bit.
arch/Kconfig | 4 +++
include/asm-generic/Kbuild | 1 +
include/asm-generic/unwind_user_types.h | 5 ++++
include/linux/unwind_user.h | 13 +++++++++
include/linux/unwind_user_types.h | 7 +++++
kernel/unwind/user.c | 36 ++++++++++++++++++++++---
6 files changed, 62 insertions(+), 4 deletions(-)
create mode 100644 include/asm-generic/unwind_user_types.h
diff --git a/arch/Kconfig b/arch/Kconfig
index 8e3fd723bd74..2c41d3072910 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -442,6 +442,10 @@ config HAVE_UNWIND_USER_FP
bool
select UNWIND_USER
+config HAVE_UNWIND_USER_COMPAT_FP
+ bool
+ depends on HAVE_UNWIND_USER_FP
+
config HAVE_PERF_REGS
bool
help
diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index 295c94a3ccc1..b797a2434396 100644
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -60,6 +60,7 @@ mandatory-y += topology.h
mandatory-y += trace_clock.h
mandatory-y += uaccess.h
mandatory-y += unwind_user.h
+mandatory-y += unwind_user_types.h
mandatory-y += vermagic.h
mandatory-y += vga.h
mandatory-y += video.h
diff --git a/include/asm-generic/unwind_user_types.h b/include/asm-generic/unwind_user_types.h
new file mode 100644
index 000000000000..f568b82e52cd
--- /dev/null
+++ b/include/asm-generic/unwind_user_types.h
@@ -0,0 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_UNWIND_USER_TYPES_H
+#define _ASM_GENERIC_UNWIND_USER_TYPES_H
+
+#endif /* _ASM_GENERIC_UNWIND_USER_TYPES_H */
diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h
index a405111c41b0..c70da8f7e54c 100644
--- a/include/linux/unwind_user.h
+++ b/include/linux/unwind_user.h
@@ -9,6 +9,19 @@
#define ARCH_INIT_USER_FP_FRAME
#endif
+#ifndef ARCH_INIT_USER_COMPAT_FP_FRAME
+ #define ARCH_INIT_USER_COMPAT_FP_FRAME
+ #define in_compat_mode(regs) false
+#endif
+
+#ifndef arch_unwind_user_init
+static inline void arch_unwind_user_init(struct unwind_user_state *state, struct pt_regs *reg) {}
+#endif
+
+#ifndef arch_unwind_user_next
+static inline void arch_unwind_user_next(struct unwind_user_state *state) {}
+#endif
+
int unwind_user_start(struct unwind_user_state *state);
int unwind_user_next(struct unwind_user_state *state);
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index 65bd070eb6b0..0b6563951ca4 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -3,10 +3,16 @@
#define _LINUX_UNWIND_USER_TYPES_H
#include <linux/types.h>
+#include <asm/unwind_user_types.h>
+
+#ifndef arch_unwind_user_state
+struct arch_unwind_user_state {};
+#endif
enum unwind_user_type {
UNWIND_USER_TYPE_NONE,
UNWIND_USER_TYPE_FP,
+ UNWIND_USER_TYPE_COMPAT_FP,
};
struct unwind_stacktrace {
@@ -25,6 +31,7 @@ struct unwind_user_state {
unsigned long ip;
unsigned long sp;
unsigned long fp;
+ struct arch_unwind_user_state arch;
enum unwind_user_type type;
bool done;
};
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 4fc550356b33..29e1f497a26e 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -12,12 +12,32 @@ static struct unwind_user_frame fp_frame = {
ARCH_INIT_USER_FP_FRAME
};
+static struct unwind_user_frame compat_fp_frame = {
+ ARCH_INIT_USER_COMPAT_FP_FRAME
+};
+
static inline bool fp_state(struct unwind_user_state *state)
{
return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP) &&
state->type == UNWIND_USER_TYPE_FP;
}
+static inline bool compat_state(struct unwind_user_state *state)
+{
+ return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_COMPAT_FP) &&
+ state->type == UNWIND_USER_TYPE_COMPAT_FP;
+}
+
+#define UNWIND_GET_USER_LONG(to, from, state) \
+({ \
+ int __ret; \
+ if (compat_state(state)) \
+ __ret = get_user(to, (u32 __user *)(from)); \
+ else \
+ __ret = get_user(to, (unsigned long __user *)(from)); \
+ __ret; \
+})
+
int unwind_user_next(struct unwind_user_state *state)
{
struct unwind_user_frame *frame;
@@ -26,7 +46,9 @@ int unwind_user_next(struct unwind_user_state *state)
if (state->done)
return -EINVAL;
- if (fp_state(state))
+ if (compat_state(state))
+ frame = &compat_fp_frame;
+ else if (fp_state(state))
frame = &fp_frame;
else
goto the_end;
@@ -37,10 +59,10 @@ int unwind_user_next(struct unwind_user_state *state)
if (cfa <= state->sp)
goto the_end;
- if (get_user(ra, (unsigned long *)(cfa + frame->ra_off)))
+ if (UNWIND_GET_USER_LONG(ra, cfa + frame->ra_off, state))
goto the_end;
- if (frame->fp_off && get_user(fp, (unsigned long __user *)(cfa + frame->fp_off)))
+ if (frame->fp_off && UNWIND_GET_USER_LONG(fp, cfa + frame->fp_off, state))
goto the_end;
state->ip = ra;
@@ -48,6 +70,8 @@ int unwind_user_next(struct unwind_user_state *state)
if (frame->fp_off)
state->fp = fp;
+ arch_unwind_user_next(state);
+
return 0;
the_end:
@@ -66,7 +90,9 @@ int unwind_user_start(struct unwind_user_state *state)
return -EINVAL;
}
- if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP))
+ if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_COMPAT_FP) && in_compat_mode(regs))
+ state->type = UNWIND_USER_TYPE_COMPAT_FP;
+ else if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP))
state->type = UNWIND_USER_TYPE_FP;
else
state->type = UNWIND_USER_TYPE_NONE;
@@ -75,6 +101,8 @@ int unwind_user_start(struct unwind_user_state *state)
state->sp = user_stack_pointer(regs);
state->fp = frame_pointer(regs);
+ arch_unwind_user_init(state, regs);
+
return 0;
}
--
2.47.2On Tue, Jun 10, 2025 at 08:54:24PM -0400, Steven Rostedt wrote:
> +#ifndef arch_unwind_user_init
> +static inline void arch_unwind_user_init(struct unwind_user_state *state, struct pt_regs *reg) {}
> +#endif
> +
> +#ifndef arch_unwind_user_next
> +static inline void arch_unwind_user_next(struct unwind_user_state *state) {}
> +#endif
The purpose of these arch hooks is so far mysterious. No comments, no
changelog, no nothing.
On Wed, 18 Jun 2025 15:47:58 +0200
Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Jun 10, 2025 at 08:54:24PM -0400, Steven Rostedt wrote:
>
> > +#ifndef arch_unwind_user_init
> > +static inline void arch_unwind_user_init(struct unwind_user_state *state, struct pt_regs *reg) {}
> > +#endif
> > +
> > +#ifndef arch_unwind_user_next
> > +static inline void arch_unwind_user_next(struct unwind_user_state *state) {}
> > +#endif
>
> The purpose of these arch hooks is so far mysterious. No comments, no
> changelog, no nothing.
I'll add comments.
It's used later in the x86 compat code to allow the architecture to do any
special initialization or to handling moving to the next frame.
From patch 14:
+#define in_compat_mode(regs) !user_64bit_mode(regs)
+
+static inline void arch_unwind_user_init(struct unwind_user_state *state,
+ struct pt_regs *regs)
+{
+ unsigned long cs_base, ss_base;
+
+ if (state->type != UNWIND_USER_TYPE_COMPAT_FP)
+ return;
+
+ scoped_guard(irqsave) {
+ cs_base = segment_base_address(regs->cs);
+ ss_base = segment_base_address(regs->ss);
+ }
+
+ state->arch.cs_base = cs_base;
+ state->arch.ss_base = ss_base;
+
+ state->ip += cs_base;
+ state->sp += ss_base;
+ state->fp += ss_base;
+}
+#define arch_unwind_user_init arch_unwind_user_init
+
+static inline void arch_unwind_user_next(struct unwind_user_state *state)
+{
+ if (state->type != UNWIND_USER_TYPE_COMPAT_FP)
+ return;
+
+ state->ip += state->arch.cs_base;
+ state->fp += state->arch.ss_base;
+}
+#define arch_unwind_user_next arch_unwind_user_next
-- Steve
On Wed, Jun 18, 2025 at 11:18:40AM -0400, Steven Rostedt wrote:
> On Wed, 18 Jun 2025 15:47:58 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Tue, Jun 10, 2025 at 08:54:24PM -0400, Steven Rostedt wrote:
> >
> > > +#ifndef arch_unwind_user_init
> > > +static inline void arch_unwind_user_init(struct unwind_user_state *state, struct pt_regs *reg) {}
> > > +#endif
> > > +
> > > +#ifndef arch_unwind_user_next
> > > +static inline void arch_unwind_user_next(struct unwind_user_state *state) {}
> > > +#endif
> >
> > The purpose of these arch hooks is so far mysterious. No comments, no
> > changelog, no nothing.
>
> I'll add comments.
How about you introduce the hooks when they're actually needed instead?
On Thu, 19 Jun 2025 09:51:03 +0200 Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > The purpose of these arch hooks is so far mysterious. No comments, no > > > changelog, no nothing. > > > > I'll add comments. > > How about you introduce the hooks when they're actually needed instead? OK. Then I'll move the hooks to the later patch. -- Steve
On Tue, Jun 10, 2025 at 08:54:24PM -0400, Steven Rostedt wrote:
> diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
> index 4fc550356b33..29e1f497a26e 100644
> --- a/kernel/unwind/user.c
> +++ b/kernel/unwind/user.c
> @@ -12,12 +12,32 @@ static struct unwind_user_frame fp_frame = {
> ARCH_INIT_USER_FP_FRAME
> };
>
> +static struct unwind_user_frame compat_fp_frame = {
> + ARCH_INIT_USER_COMPAT_FP_FRAME
> +};
> +
> static inline bool fp_state(struct unwind_user_state *state)
> {
> return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP) &&
> state->type == UNWIND_USER_TYPE_FP;
> }
>
> +static inline bool compat_state(struct unwind_user_state *state)
Consistency would mandate this thing be called: compat_fp_state().
> +{
> + return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_COMPAT_FP) &&
> + state->type == UNWIND_USER_TYPE_COMPAT_FP;
> +}
> +
> +#define UNWIND_GET_USER_LONG(to, from, state) \
Do we have to shout this?
> +({ \
> + int __ret; \
> + if (compat_state(state)) \
> + __ret = get_user(to, (u32 __user *)(from)); \
> + else \
> + __ret = get_user(to, (unsigned long __user *)(from)); \
> + __ret; \
> +})
> +
> int unwind_user_next(struct unwind_user_state *state)
> {
> struct unwind_user_frame *frame;
On Wed, 18 Jun 2025 15:46:41 +0200
Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Jun 10, 2025 at 08:54:24PM -0400, Steven Rostedt wrote:
> > diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
> > index 4fc550356b33..29e1f497a26e 100644
> > --- a/kernel/unwind/user.c
> > +++ b/kernel/unwind/user.c
> > @@ -12,12 +12,32 @@ static struct unwind_user_frame fp_frame = {
> > ARCH_INIT_USER_FP_FRAME
> > };
> >
> > +static struct unwind_user_frame compat_fp_frame = {
> > + ARCH_INIT_USER_COMPAT_FP_FRAME
> > +};
> > +
> > static inline bool fp_state(struct unwind_user_state *state)
> > {
> > return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP) &&
> > state->type == UNWIND_USER_TYPE_FP;
> > }
> >
> > +static inline bool compat_state(struct unwind_user_state *state)
>
> Consistency would mandate this thing be called: compat_fp_state().
Sure. Will update it.
>
> > +{
> > + return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_COMPAT_FP) &&
> > + state->type == UNWIND_USER_TYPE_COMPAT_FP;
> > +}
> > +
> > +#define UNWIND_GET_USER_LONG(to, from, state) \
>
> Do we have to shout this?
Don't we usually shout macros?
-- Steve
>
> > +({ \
> > + int __ret; \
> > + if (compat_state(state)) \
> > + __ret = get_user(to, (u32 __user *)(from)); \
> > + else \
> > + __ret = get_user(to, (unsigned long __user *)(from)); \
> > + __ret; \
> > +})
> > +
> > int unwind_user_next(struct unwind_user_state *state)
> > {
> > struct unwind_user_frame *frame;
On Wed, 18 Jun 2025 at 08:10, Steven Rostedt <rostedt@goodmis.org> wrote:
>
> Don't we usually shout macros?
Not really. It's more about "we shout about macros when they _behave_
like macros".
So typically we do all upper-case for things that are constants
(whether enums or macros, actually) or when they don't act like normal
functions.
But when it's not particularly important that it's a macro, and it
could have been a function (but maybe it was just simpler to use a
macro for whatever reason), we typically don't use all upper-case.
In this case, I have to agree with PeterZ that this just looks odd:
- if (get_user(ra, (unsigned long *)(cfa + frame->ra_off)))
+ if (UNWIND_GET_USER_LONG(ra, cfa + frame->ra_off, state))
why is UNWIND_GET_USER_LONG() so loud when it just replaces "get_user()"?
Note that "get_user()" itself is a macro, and is lower-case, even
though you couldn't actually do it as a function (because it changes
its first argument in place).
Linus
On Wed, 18 Jun 2025 10:52:22 -0700 Linus Torvalds <torvalds@linux-foundation.org> wrote: > In this case, I have to agree with PeterZ that this just looks odd: > > - if (get_user(ra, (unsigned long *)(cfa + frame->ra_off))) > + if (UNWIND_GET_USER_LONG(ra, cfa + frame->ra_off, state)) > > why is UNWIND_GET_USER_LONG() so loud when it just replaces "get_user()"? > > Note that "get_user()" itself is a macro, and is lower-case, even > though you couldn't actually do it as a function (because it changes > its first argument in place). OK, I'll make it lower case. Thanks! -- Steve
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