From: Uros Bizjak <ubizjak@gmail.com>
Date: Mon, 8 Sep 2025 12:38:22 +0000 (+0200)
Subject: x86: Define atomic_exchange_acq using __atomic_exchange_n
X-Git-Tag: glibc-2.43~555
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=935ee691bce7aa8c957714deea4868e5aefb52c9;p=thirdparty%2Fglibc.git

x86: Define atomic_exchange_acq using __atomic_exchange_n

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

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.  */