[PATCH] nptl: x86_64: Use same code for CURRENT_STACK_FRAME and stackinfo_get_sp

[Noah Goldstein]

On Tue, Aug 30, 2022 at 5:08 AM Adhemerval Zanella via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> It avoids the possible warning of uninitialized 'frame' variable when
> building with clang:
>
>   ../sysdeps/nptl/jmp-unwind.c:27:42: error: variable 'frame' is
>   uninitialized when used here [-Werror,-Wuninitialized]
>     __pthread_cleanup_upto (env->__jmpbuf, CURRENT_STACK_FRAME);
>
> The resulting code is similar to CURRENT_STACK_FRAME.
>
> Checked on x86_64-linux-gnu.
> ---
>  sysdeps/x86/nptl/pthreaddef.h | 4 +++-
>  sysdeps/x86_64/stackinfo.h    | 4 +++-
>  2 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/sysdeps/x86/nptl/pthreaddef.h b/sysdeps/x86/nptl/pthreaddef.h
> index 63fdbcb27c..7df65931a3 100644
> --- a/sysdeps/x86/nptl/pthreaddef.h
> +++ b/sysdeps/x86/nptl/pthreaddef.h
> @@ -42,7 +42,9 @@
>  #ifdef __x86_64__
>  /* The frame pointer is not usable.  */
>  # define CURRENT_STACK_FRAME \
> -  ({ register char *frame __asm__("rsp"); frame; })
> +  ({ register void * p__ __asm__(RSP_REG); \
> +     asm volatile("" : "=r" (p__)); \
> +     p__; })
>  #else
>  # define CURRENT_STACK_FRAME   __builtin_frame_address (0)
>  #endif
> diff --git a/sysdeps/x86_64/stackinfo.h b/sysdeps/x86_64/stackinfo.h
> index 34c9d0b576..7354632132 100644
> --- a/sysdeps/x86_64/stackinfo.h
> +++ b/sysdeps/x86_64/stackinfo.h
> @@ -40,7 +40,9 @@
>     for which they need to act as barriers as well, hence the additional
>     (unnecessary) parameters.  */
>  #define stackinfo_get_sp() \
> -  ({ void *p__; asm volatile ("mov %%" RSP_REG ", %0" : "=r" (p__)); p__; })
> +  ({ register void * p__ __asm__(RSP_REG); \
> +     asm volatile("" : "=r" (p__)); \
> +     p__; })

This change addresses a different issue. Maybe two separate commits?

Otherwise LGTM.
>  #define stackinfo_sub_sp(ptr) \
>    ({ ptrdiff_t d__;                                            \
>       asm volatile ("sub %%" RSP_REG " , %0" : "=r" (d__) : "0" (ptr)); \
> --
> 2.34.1
>