[PATCH 4/5] x86: Define atomic_exchange_acq using __atomic_exchange_n

[Adhemerval Zanella Netto]

On 08/09/25 09:38, Uros Bizjak wrote:
> The resulting libc.so is identical on both x86_64 and
> i386 targets compared to unpatched builds:
> 
> $ sha1sum libc-x86_64-old.so libc-x86_64-new.so
> 74eca1b87f2ecc9757a984c089a582b7615d93e7  libc-x86_64-old.so
> 74eca1b87f2ecc9757a984c089a582b7615d93e7  libc-x86_64-new.so
> $ sha1sum libc-i386-old.so libc-i386-new.so
> 882bbab8324f79f4fbc85224c4c914fc6822ece7  libc-i386-old.so
> 882bbab8324f79f4fbc85224c4c914fc6822ece7  libc-i386-new.so
> 
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: Florian Weimer <fweimer@redhat.com>
> Cc: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
> Cc: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
> Cc: Collin Funk <collin.funk1@gmail.com>
> Cc: H.J.Lu <hjl.tools@gmail.com>
> Cc: Carlos O'Donell <carlos@redhat.com>

LGTM, thanks.

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

> ---
>  sysdeps/x86/atomic-machine.h | 29 +----------------------------
>  1 file changed, 1 insertion(+), 28 deletions(-)
> 
> diff --git a/sysdeps/x86/atomic-machine.h b/sysdeps/x86/atomic-machine.h
> index c0c2c3437a..ebe8e978e5 100644
> --- a/sysdeps/x86/atomic-machine.h
> +++ b/sysdeps/x86/atomic-machine.h
> @@ -19,9 +19,6 @@
>  #ifndef _X86_ATOMIC_MACHINE_H
>  #define _X86_ATOMIC_MACHINE_H 1
>  
> -#include <stdint.h>
> -#include <libc-pointer-arith.h>		/* For cast_to_integer.  */
> -
>  #define USE_ATOMIC_COMPILER_BUILTINS	1
>  
>  #ifdef __x86_64__
> @@ -41,32 +38,8 @@
>  #define atomic_compare_and_exchange_bool_acq(mem, newval, oldval) \
>    (! __sync_bool_compare_and_swap (mem, oldval, newval))
>  
> -/* Note that we need no lock prefix.  */
>  #define atomic_exchange_acq(mem, newvalue) \
> -  ({ __typeof (*mem) result;						      \
> -     if (sizeof (*mem) == 1)						      \
> -       __asm __volatile ("xchgb %b0, %1"				      \
> -			 : "=q" (result), "=m" (*mem)			      \
> -			 : "0" (newvalue), "m" (*mem));			      \
> -     else if (sizeof (*mem) == 2)					      \
> -       __asm __volatile ("xchgw %w0, %1"				      \
> -			 : "=r" (result), "=m" (*mem)			      \
> -			 : "0" (newvalue), "m" (*mem));			      \
> -     else if (sizeof (*mem) == 4)					      \
> -       __asm __volatile ("xchgl %0, %1"					      \
> -			 : "=r" (result), "=m" (*mem)			      \
> -			 : "0" (newvalue), "m" (*mem));			      \
> -     else if (__HAVE_64B_ATOMICS)					      \
> -       __asm __volatile ("xchgq %q0, %1"				      \
> -			 : "=r" (result), "=m" (*mem)			      \
> -			 : "0" ((int64_t) cast_to_integer (newvalue)),        \
> -			   "m" (*mem));					      \
> -     else								      \
> -       {								      \
> -	 result = 0;							      \
> -	 __atomic_link_error ();					      \
> -       }								      \
> -     result; })
> +  __atomic_exchange_n (mem, newvalue, __ATOMIC_ACQUIRE)
>  
>  /* ??? Remove when catomic_exchange_and_add
>     fallback uses __atomic_fetch_add.  */