[PATCH] x86: uapi: ptrace: guard register offset macros with __ASSEMBLER__ or __FRAME_OFFSETS

[PATCH] x86: uapi: ptrace: guard register offset macros with __ASSEMBLER__ or __FRAME_OFFSETS

[Nick Desaulniers]

The register offset macros in <asm/ptrace-abi.h> are guarded by
`defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)` for 64-bit, but
were left unguarded for 32-bit. This causes havoc for userspace that
happens to use identifiers colliding with these short macro names
(e.g., EBX, ECX, EAX, DS, ES, FS, GS, CS, SS). Without this guard,
userspace is forced to be super extra careful with include ordering to
minimize the chance of collision.

Wrap both the 32-bit and 64-bit register definitions under
`#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)`, and ensure
User-Mode Linux (UML) defines `__FRAME_OFFSETS` for 32-bit as well.

Assisted-by: Gemini
Link: https://github.com/llvm/llvm-project/issues/217413
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 arch/x86/include/uapi/asm/ptrace-abi.h | 4 ++--
 arch/x86/um/asm/ptrace.h               | 4 +---
 arch/x86/um/ptrace_32.c                | 1 +
 3 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/uapi/asm/ptrace-abi.h b/arch/x86/include/uapi/asm/ptrace-abi.h
index 5823584dea13..3656955c6faa 100644
--- a/arch/x86/include/uapi/asm/ptrace-abi.h
+++ b/arch/x86/include/uapi/asm/ptrace-abi.h
@@ -2,6 +2,7 @@
 #ifndef _ASM_X86_PTRACE_ABI_H
 #define _ASM_X86_PTRACE_ABI_H
 
+#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)
 #ifdef __i386__
 
 #define EBX 0
@@ -25,7 +26,6 @@
 
 #else /* __i386__ */
 
-#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)
 /*
  * C ABI says these regs are callee-preserved. They aren't saved on kernel entry
  * unless syscall needs a complete, fully filled "struct pt_regs".
@@ -57,12 +57,12 @@
 #define EFLAGS 144
 #define RSP 152
 #define SS 160
-#endif /* __ASSEMBLER__ */
 
 /* top of stack page */
 #define FRAME_SIZE 168
 
 #endif /* !__i386__ */
+#endif /* defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS) */
 
 /* Arbitrarily choose the same ptrace numbers as used by the Sparc code. */
 #define PTRACE_GETREGS            12
diff --git a/arch/x86/um/asm/ptrace.h b/arch/x86/um/asm/ptrace.h
index 2641d28d115c..439c4151f6b7 100644
--- a/arch/x86/um/asm/ptrace.h
+++ b/arch/x86/um/asm/ptrace.h
@@ -13,9 +13,7 @@ enum {
 };
 
 #include <linux/compiler.h>
-#ifndef CONFIG_X86_32
-#define __FRAME_OFFSETS /* Needed to get the R* macros */
-#endif
+#define __FRAME_OFFSETS /* Needed to get the register macros */
 #include <asm/ptrace-generic.h>
 
 #define user_mode(r) UPT_IS_USER(&(r)->regs)
diff --git a/arch/x86/um/ptrace_32.c b/arch/x86/um/ptrace_32.c
index 3af3cb821524..9e9155b0e918 100644
--- a/arch/x86/um/ptrace_32.c
+++ b/arch/x86/um/ptrace_32.c
@@ -7,6 +7,7 @@
 #include <linux/sched.h>
 #include <linux/uaccess.h>
 #include <linux/regset.h>
+#define __FRAME_OFFSETS
 #include <asm/ptrace-abi.h>
 #include <registers.h>
 #include <skas.h>

---
base-commit: 26260251022fbc2f248a3d747a9b2b961b18d2d8
change-id: 20260821-ptrace_uapi-462350036cbd

Best regards,
-- 
Nick Desaulniers <ndesaulniers@google.com>

Re: [PATCH] x86: uapi: ptrace: guard register offset macros with __ASSEMBLER__ or __FRAME_OFFSETS

[Nick Desaulniers]

On Fri, Aug 21, 2026 at 3:46 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> The register offset macros in <asm/ptrace-abi.h> are guarded by
> `defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)` for 64-bit, but
> were left unguarded for 32-bit. This causes havoc for userspace that
> happens to use identifiers colliding with these short macro names
> (e.g., EBX, ECX, EAX, DS, ES, FS, GS, CS, SS). Without this guard,
> userspace is forced to be super extra careful with include ordering to
> minimize the chance of collision.
>
> Wrap both the 32-bit and 64-bit register definitions under
> `#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)`, and ensure
> User-Mode Linux (UML) defines `__FRAME_OFFSETS` for 32-bit as well.
>
> Assisted-by: Gemini
> Link: https://github.com/llvm/llvm-project/issues/217413
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

+ enh (who pulled this into android for testing)

Oleg, can I get an ack/nack here? Or someone who knows better the
history of UAPI headers?

(I think the Assisted-by tags need `LLM` now IIUC? Assisted-by: LLM Gemini)

We've worked around this now in lldb-server, but figured it might be
nice to clean this up for the rest of userspace, too.

> ---
>  arch/x86/include/uapi/asm/ptrace-abi.h | 4 ++--
>  arch/x86/um/asm/ptrace.h               | 4 +---
>  arch/x86/um/ptrace_32.c                | 1 +
>  3 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/uapi/asm/ptrace-abi.h b/arch/x86/include/uapi/asm/ptrace-abi.h
> index 5823584dea13..3656955c6faa 100644
> --- a/arch/x86/include/uapi/asm/ptrace-abi.h
> +++ b/arch/x86/include/uapi/asm/ptrace-abi.h
> @@ -2,6 +2,7 @@
>  #ifndef _ASM_X86_PTRACE_ABI_H
>  #define _ASM_X86_PTRACE_ABI_H
>
> +#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)
>  #ifdef __i386__
>
>  #define EBX 0
> @@ -25,7 +26,6 @@
>
>  #else /* __i386__ */
>
> -#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)
>  /*
>   * C ABI says these regs are callee-preserved. They aren't saved on kernel entry
>   * unless syscall needs a complete, fully filled "struct pt_regs".
> @@ -57,12 +57,12 @@
>  #define EFLAGS 144
>  #define RSP 152
>  #define SS 160
> -#endif /* __ASSEMBLER__ */
>
>  /* top of stack page */
>  #define FRAME_SIZE 168
>
>  #endif /* !__i386__ */
> +#endif /* defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS) */
>
>  /* Arbitrarily choose the same ptrace numbers as used by the Sparc code. */
>  #define PTRACE_GETREGS            12
> diff --git a/arch/x86/um/asm/ptrace.h b/arch/x86/um/asm/ptrace.h
> index 2641d28d115c..439c4151f6b7 100644
> --- a/arch/x86/um/asm/ptrace.h
> +++ b/arch/x86/um/asm/ptrace.h
> @@ -13,9 +13,7 @@ enum {
>  };
>
>  #include <linux/compiler.h>
> -#ifndef CONFIG_X86_32
> -#define __FRAME_OFFSETS /* Needed to get the R* macros */
> -#endif
> +#define __FRAME_OFFSETS /* Needed to get the register macros */
>  #include <asm/ptrace-generic.h>
>
>  #define user_mode(r) UPT_IS_USER(&(r)->regs)
> diff --git a/arch/x86/um/ptrace_32.c b/arch/x86/um/ptrace_32.c
> index 3af3cb821524..9e9155b0e918 100644
> --- a/arch/x86/um/ptrace_32.c
> +++ b/arch/x86/um/ptrace_32.c
> @@ -7,6 +7,7 @@
>  #include <linux/sched.h>
>  #include <linux/uaccess.h>
>  #include <linux/regset.h>
> +#define __FRAME_OFFSETS
>  #include <asm/ptrace-abi.h>
>  #include <registers.h>
>  #include <skas.h>
>
> ---
> base-commit: 26260251022fbc2f248a3d747a9b2b961b18d2d8
> change-id: 20260821-ptrace_uapi-462350036cbd
>
> Best regards,
> --
> Nick Desaulniers <ndesaulniers@google.com>
>


-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] x86: uapi: ptrace: guard register offset macros with __ASSEMBLER__ or __FRAME_OFFSETS

[enh]

On Tue, Sep 1, 2026 at 5:45 PM Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> On Fri, Aug 21, 2026 at 3:46 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > The register offset macros in <asm/ptrace-abi.h> are guarded by
> > `defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)` for 64-bit, but
> > were left unguarded for 32-bit. This causes havoc for userspace that
> > happens to use identifiers colliding with these short macro names
> > (e.g., EBX, ECX, EAX, DS, ES, FS, GS, CS, SS). Without this guard,
> > userspace is forced to be super extra careful with include ordering to
> > minimize the chance of collision.
> >
> > Wrap both the 32-bit and 64-bit register definitions under
> > `#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)`, and ensure
> > User-Mode Linux (UML) defines `__FRAME_OFFSETS` for 32-bit as well.
> >
> > Assisted-by: Gemini
> > Link: https://github.com/llvm/llvm-project/issues/217413
> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
>
> + enh (who pulled this into android for testing)

for those who don't know me, i've been Android's libc maintainer for a
while now [was https://blog.linuxplumbersconf.org/2014/ocw/proposals/2337
really that long ago?!]... i applied this patch to Android's libc's
copy of the uapi headers (because Android uses the uapi headers
directly, unlike glibc, and exposes this header transitively from
<sys/ptrace.h>, also unlike glibc), and everything still built without
problems.

this does solve a real problem for us: llvm's coding style means they
have a lot of "FS" and "SS" identifiers that conflict with these
macros, and we see a conflict every few years.

Tested-by: Elliott Hughes <enh@google.com>

> Oleg, can I get an ack/nack here? Or someone who knows better the
> history of UAPI headers?
>
> (I think the Assisted-by tags need `LLM` now IIUC? Assisted-by: LLM Gemini)
>
> We've worked around this now in lldb-server, but figured it might be
> nice to clean this up for the rest of userspace, too.
>
> > ---
> >  arch/x86/include/uapi/asm/ptrace-abi.h | 4 ++--
> >  arch/x86/um/asm/ptrace.h               | 4 +---
> >  arch/x86/um/ptrace_32.c                | 1 +
> >  3 files changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/include/uapi/asm/ptrace-abi.h b/arch/x86/include/uapi/asm/ptrace-abi.h
> > index 5823584dea13..3656955c6faa 100644
> > --- a/arch/x86/include/uapi/asm/ptrace-abi.h
> > +++ b/arch/x86/include/uapi/asm/ptrace-abi.h
> > @@ -2,6 +2,7 @@
> >  #ifndef _ASM_X86_PTRACE_ABI_H
> >  #define _ASM_X86_PTRACE_ABI_H
> >
> > +#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)
> >  #ifdef __i386__
> >
> >  #define EBX 0
> > @@ -25,7 +26,6 @@
> >
> >  #else /* __i386__ */
> >
> > -#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)
> >  /*
> >   * C ABI says these regs are callee-preserved. They aren't saved on kernel entry
> >   * unless syscall needs a complete, fully filled "struct pt_regs".
> > @@ -57,12 +57,12 @@
> >  #define EFLAGS 144
> >  #define RSP 152
> >  #define SS 160
> > -#endif /* __ASSEMBLER__ */
> >
> >  /* top of stack page */
> >  #define FRAME_SIZE 168
> >
> >  #endif /* !__i386__ */
> > +#endif /* defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS) */
> >
> >  /* Arbitrarily choose the same ptrace numbers as used by the Sparc code. */
> >  #define PTRACE_GETREGS            12
> > diff --git a/arch/x86/um/asm/ptrace.h b/arch/x86/um/asm/ptrace.h
> > index 2641d28d115c..439c4151f6b7 100644
> > --- a/arch/x86/um/asm/ptrace.h
> > +++ b/arch/x86/um/asm/ptrace.h
> > @@ -13,9 +13,7 @@ enum {
> >  };
> >
> >  #include <linux/compiler.h>
> > -#ifndef CONFIG_X86_32
> > -#define __FRAME_OFFSETS /* Needed to get the R* macros */
> > -#endif
> > +#define __FRAME_OFFSETS /* Needed to get the register macros */
> >  #include <asm/ptrace-generic.h>
> >
> >  #define user_mode(r) UPT_IS_USER(&(r)->regs)
> > diff --git a/arch/x86/um/ptrace_32.c b/arch/x86/um/ptrace_32.c
> > index 3af3cb821524..9e9155b0e918 100644
> > --- a/arch/x86/um/ptrace_32.c
> > +++ b/arch/x86/um/ptrace_32.c
> > @@ -7,6 +7,7 @@
> >  #include <linux/sched.h>
> >  #include <linux/uaccess.h>
> >  #include <linux/regset.h>
> > +#define __FRAME_OFFSETS
> >  #include <asm/ptrace-abi.h>
> >  #include <registers.h>
> >  #include <skas.h>
> >
> > ---
> > base-commit: 26260251022fbc2f248a3d747a9b2b961b18d2d8
> > change-id: 20260821-ptrace_uapi-462350036cbd
> >
> > Best regards,
> > --
> > Nick Desaulniers <ndesaulniers@google.com>
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers

Re: [PATCH] x86: uapi: ptrace: guard register offset macros with __ASSEMBLER__ or __FRAME_OFFSETS

[Oleg Nesterov]

On 09/01, Nick Desaulniers wrote:
>
> On Fri, Aug 21, 2026 at 3:46 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > The register offset macros in <asm/ptrace-abi.h> are guarded by
> > `defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)` for 64-bit, but
> > were left unguarded for 32-bit. This causes havoc for userspace that
> > happens to use identifiers colliding with these short macro names
> > (e.g., EBX, ECX, EAX, DS, ES, FS, GS, CS, SS). Without this guard,
> > userspace is forced to be super extra careful with include ordering to
> > minimize the chance of collision.
> >
> > Wrap both the 32-bit and 64-bit register definitions under
> > `#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)`, and ensure
> > User-Mode Linux (UML) defines `__FRAME_OFFSETS` for 32-bit as well.
> >
> > Assisted-by: Gemini
> > Link: https://github.com/llvm/llvm-project/issues/217413
> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
>
> + enh (who pulled this into android for testing)
>
> Oleg, can I get an ack/nack here?

Oh... there is a little problem, I don't understand the usage of
(magic to me) __FRAME_OFFSETS ;)

> Or someone who knows better the
> history of UAPI headers?

Certainly not me....

OK. I'll try to read this patch tomorrow with the clear head after sleep.

Oleg.

Re: [PATCH] x86: uapi: ptrace: guard register offset macros with __ASSEMBLER__ or __FRAME_OFFSETS

[Nick Desaulniers]

On Wed, Sep 2, 2026 at 10:29 AM Oleg Nesterov <oleg@redhat.com> wrote:
>
> On 09/01, Nick Desaulniers wrote:
> >
> > On Fri, Aug 21, 2026 at 3:46 PM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > The register offset macros in <asm/ptrace-abi.h> are guarded by
> > > `defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)` for 64-bit, but
> > > were left unguarded for 32-bit. This causes havoc for userspace that
> > > happens to use identifiers colliding with these short macro names
> > > (e.g., EBX, ECX, EAX, DS, ES, FS, GS, CS, SS). Without this guard,
> > > userspace is forced to be super extra careful with include ordering to
> > > minimize the chance of collision.
> > >
> > > Wrap both the 32-bit and 64-bit register definitions under
> > > `#if defined(__ASSEMBLER__) || defined(__FRAME_OFFSETS)`, and ensure
> > > User-Mode Linux (UML) defines `__FRAME_OFFSETS` for 32-bit as well.
> > >
> > > Assisted-by: Gemini
> > > Link: https://github.com/llvm/llvm-project/issues/217413
> > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> >
> > + enh (who pulled this into android for testing)
> >
> > Oleg, can I get an ack/nack here?
>
> Oh... there is a little problem, I don't understand the usage of
> (magic to me) __FRAME_OFFSETS ;)

Yeah, my Assisted by tag is from asking Gemini to triple check my
patch before posting, and it pointing out to me from a local review:
"did you intend to break the arch/x86/um/ C uses of these macro
defines?"  So I'm just matching an existing pattern in arch/x86/um/
for 64b with the __FRAME_OFFSETS parts of this patch.

The patch started off as "why are the 64b macros behind the
__ASSEMBLER__ preprocessor guards, but not the 32b ones?"  I went back
through the pre-git history tree, and FWICT, those macros have always
been guarded for 64b, since the introduction of x86_64 support itself.
Dunno if anyone remembers anymore _why_ the 32b macro defines don't
have that guard (chesterton's fence?), but to me, IMO, it looks like a
mistake.

Hence this patch.  PTAL

>
> > Or someone who knows better the
> > history of UAPI headers?
>
> Certainly not me....
>
> OK. I'll try to read this patch tomorrow with the clear head after sleep.

Thanks for taking a look.
-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] x86: uapi: ptrace: guard register offset macros with __ASSEMBLER__ or __FRAME_OFFSETS

[Johannes Berg]

On Fri, 2026-08-21 at 15:45 -0700, Nick Desaulniers wrote:
> 
>  arch/x86/um/asm/ptrace.h               | 4 +---
>  arch/x86/um/ptrace_32.c                | 1 +

This seems like a simple adjustment for what you need to do in x86, so
that's OK, but I don't think we'll take this through the UML tree.

But for UML you can have my

Acked-by: Johannes Berg <johannes@sipsolutions.net>

johannes