[PATCH 3/3] i386: Replace inline asm rotates in pointer_guard with stdc_rotate_{left, right}

[Adhemerval Zanella Netto]

On 06/05/26 15:42, Uros Bizjak wrote:
> Use the C23 <stdbit.h> rotation helpers instead of inline assembly
> for pointer mangling and demangling on i386.
> 
> The PTR_MANGLE and PTR_DEMANGLE macros previously used rol/ror
> inline asm with a constant rotation of 9. Replace these with
> stdc_rotate_left and stdc_rotate_right operating on uintptr_t,
> preserving the exact rotation count via 2 * sizeof (uintptr_t) + 1.
> 
> This change removes inline assembly, improves portability and
> readability and lets the compiler select optimal code generation.
> 
> No functional change intended.
> 
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>


> ---
>  sysdeps/unix/sysv/linux/i386/pointer_guard.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/i386/pointer_guard.h b/sysdeps/unix/sysv/linux/i386/pointer_guard.h
> index 7c142fb526..c8311be444 100644
> --- a/sysdeps/unix/sysv/linux/i386/pointer_guard.h
> +++ b/sysdeps/unix/sysv/linux/i386/pointer_guard.h
> @@ -33,16 +33,19 @@
>  #  define PTR_DEMANGLE(reg)	rorl $9, reg;				      \
>  				xorl %gs:POINTER_GUARD, reg
>  # else
> +#  include <stdbit.h>
>  #  include <tls.h>
>  #  define PTR_MANGLE(var)						      \
>      do {								      \
>        (var) = (__typeof (var)) ((uintptr_t) (var)			      \
>  				^ ((tcbhead_t __seg_gs *)0)->pointer_guard);  \
> -      asm ("roll $9, %0" : "+r" (var));					      \
> +      (var) = (__typeof (var)) stdc_rotate_left ((uintptr_t) (var),	      \
> +						 2 * sizeof (uintptr_t) + 1); \
>      } while (0)
>  #  define PTR_DEMANGLE(var)						      \
>      do {								      \
> -      asm ("rorl $9, %0" : "+r" (var));					      \
> +      (var) = (__typeof (var)) stdc_rotate_right ((uintptr_t) (var),	      \
> +						  2 * sizeof (uintptr_t) + 1); \
>        (var) = (__typeof (var)) ((uintptr_t) (var)			      \
>  				^ ((tcbhead_t __seg_gs *)0)->pointer_guard);  \
>      } while (0)