From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Date: Thu, 11 Sep 2025 13:49:47 +0000 (-0300)
Subject: Define __HAVE_64B_ATOMICS from compiler support
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=53807741fb44edb8e7c094cb5e7d4ff4e92a6ec1;p=thirdparty%2Fglibc.git

Define __HAVE_64B_ATOMICS from compiler support

Now that atomic builtins are used by default, we can rely on the
compiler to define when to use 64-bit atomic operations.

It allows the use of 64-bit atomic operations on some 32-bit ABIs where
they were not previously enabled due to missing pre-processor handling:
hppa, mips64n32, s390, and sparcv9.

Co-authored-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
Reviewed-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>
---

diff --git a/config.h.in b/config.h.in
index 5378883060..c31990705e 100644
--- a/config.h.in
+++ b/config.h.in
@@ -222,6 +222,9 @@
 /* An integer used to scale the timeout of test programs.  */
 #define TIMEOUTFACTOR 1
 
+/* Set to 1 if 64 bit atomics are supported.  */
+#undef __HAVE_64B_ATOMICS 0
+
 /*
  */
 
diff --git a/configure b/configure
index 85bfeec8a9..09d877aabb 100755
--- a/configure
+++ b/configure
@@ -7702,6 +7702,48 @@ if test "$libc_cv_gcc_builtin_memset" = yes ; then
 
 fi
 
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for 64-bit atomic support" >&5
+printf %s "checking for 64-bit atomic support... " >&6; }
+if test ${libc_cv_gcc_has_64b_atomics+y}
+then :
+  printf %s "(cached) " >&6
+else case e in #(
+  e) cat > conftest.c <<\EOF
+typedef struct { long long t; } X;
+extern void has_64b_atomics(void);
+void f(void)
+{
+  X x;
+  /* Use address of structure with 64-bit type.  This avoids incorrect
+     implementations which return true even if long long is not 64-bit aligned.
+     This works on GCC and LLVM - other cases have bugs and they disagree.  */
+  _Static_assert (__atomic_always_lock_free (sizeof (x), &x), "no_64b_atomics");
+}
+EOF
+if { ac_try='${CC-cc} -O2 -S conftest.c'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; };
+then
+  libc_cv_gcc_has_64b_atomics=yes
+else
+  libc_cv_gcc_has_64b_atomics=no
+fi
+rm -f conftest*  ;;
+esac
+fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_has_64b_atomics" >&5
+printf "%s\n" "$libc_cv_gcc_has_64b_atomics" >&6; }
+if test "$libc_cv_gcc_has_64b_atomics" = yes; then
+  printf "%s\n" "#define __HAVE_64B_ATOMICS 1" >>confdefs.h
+
+else
+  printf "%s\n" "#define __HAVE_64B_ATOMICS 0" >>confdefs.h
+
+ fi
+
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for redirection of built-in functions" >&5
 printf %s "checking for redirection of built-in functions... " >&6; }
 if test ${libc_cv_gcc_builtin_redirection+y}
diff --git a/configure.ac b/configure.ac
index 2cb49f49bc..8fb3e12343 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1493,6 +1493,33 @@ if test "$libc_cv_gcc_builtin_memset" = yes ; then
   AC_DEFINE(HAVE_BUILTIN_MEMSET)
 fi
 
+AC_CACHE_CHECK(for 64-bit atomic support, libc_cv_gcc_has_64b_atomics, [dnl
+cat > conftest.c <<\EOF
+typedef struct { long long t; } X;
+extern void has_64b_atomics(void);
+void f(void)
+{
+  X x;
+  /* Use address of structure with 64-bit type.  This avoids incorrect
+     implementations which return true even if long long is not 64-bit aligned.
+     This works on GCC and LLVM - other cases have bugs and they disagree.  */
+  _Static_assert (__atomic_always_lock_free (sizeof (x), &x), "no_64b_atomics");
+}
+EOF
+dnl
+if AC_TRY_COMMAND([${CC-cc} -O2 -S conftest.c]);
+then
+  libc_cv_gcc_has_64b_atomics=yes
+else
+  libc_cv_gcc_has_64b_atomics=no
+fi
+rm -f conftest* ])
+if test "$libc_cv_gcc_has_64b_atomics" = yes; then
+  AC_DEFINE(__HAVE_64B_ATOMICS, 1)
+else
+  AC_DEFINE(__HAVE_64B_ATOMICS, 0)
+ fi
+
 AC_CACHE_CHECK(for redirection of built-in functions, libc_cv_gcc_builtin_redirection, [dnl
 cat > conftest.c <<\EOF
 extern char *strstr (const char *, const char *) __asm ("my_strstr");
diff --git a/sysdeps/aarch64/atomic-machine.h b/sysdeps/aarch64/atomic-machine.h
index f00c4607f3..002a800358 100644
--- a/sysdeps/aarch64/atomic-machine.h
+++ b/sysdeps/aarch64/atomic-machine.h
@@ -19,7 +19,6 @@
 #ifndef _AARCH64_ATOMIC_MACHINE_H
 #define _AARCH64_ATOMIC_MACHINE_H	1
 
-#define __HAVE_64B_ATOMICS 1
 #define ATOMIC_EXCHANGE_USES_CAS 0
 
 #endif
diff --git a/sysdeps/alpha/atomic-machine.h b/sysdeps/alpha/atomic-machine.h
index 198f5dc037..9844f13079 100644
--- a/sysdeps/alpha/atomic-machine.h
+++ b/sysdeps/alpha/atomic-machine.h
@@ -17,8 +17,6 @@
 
 #include <stdint.h>
 
-#define __HAVE_64B_ATOMICS 1
-
 /* XXX Is this actually correct?  */
 #define ATOMIC_EXCHANGE_USES_CAS 1
 
diff --git a/sysdeps/arc/atomic-machine.h b/sysdeps/arc/atomic-machine.h
index 096035840a..69b9328fc8 100644
--- a/sysdeps/arc/atomic-machine.h
+++ b/sysdeps/arc/atomic-machine.h
@@ -19,8 +19,6 @@
 #ifndef _ARC_BITS_ATOMIC_H
 #define _ARC_BITS_ATOMIC_H 1
 
-#define __HAVE_64B_ATOMICS 0
-
 /* ARC does have legacy atomic EX reg, [mem] instruction but the micro-arch
    is not as optimal as LLOCK/SCOND specially for SMP.  */
 #define ATOMIC_EXCHANGE_USES_CAS 1
diff --git a/sysdeps/arm/atomic-machine.h b/sysdeps/arm/atomic-machine.h
index f728de4ba5..7aee873371 100644
--- a/sysdeps/arm/atomic-machine.h
+++ b/sysdeps/arm/atomic-machine.h
@@ -16,5 +16,4 @@
    License along with the GNU C Library.  If not, see
    <https://www.gnu.org/licenses/>.  */
 
-#define __HAVE_64B_ATOMICS 0
 #define ATOMIC_EXCHANGE_USES_CAS 1
diff --git a/sysdeps/csky/atomic-machine.h b/sysdeps/csky/atomic-machine.h
index 5d6f3d19ce..84468cd66e 100644
--- a/sysdeps/csky/atomic-machine.h
+++ b/sysdeps/csky/atomic-machine.h
@@ -19,7 +19,6 @@
 #ifndef __CSKY_ATOMIC_H_
 #define __CSKY_ATOMIC_H_
 
-#define __HAVE_64B_ATOMICS 0
 #define ATOMIC_EXCHANGE_USES_CAS 1
 
 #endif /* atomic-machine.h */
diff --git a/sysdeps/hppa/atomic-machine.h b/sysdeps/hppa/atomic-machine.h
index 839b8df596..92d386b748 100644
--- a/sysdeps/hppa/atomic-machine.h
+++ b/sysdeps/hppa/atomic-machine.h
@@ -18,8 +18,6 @@
 #ifndef _ATOMIC_MACHINE_H
 #define _ATOMIC_MACHINE_H	1
 
-#define __HAVE_64B_ATOMICS 0
-
 /* XXX Is this actually correct?  */
 #define ATOMIC_EXCHANGE_USES_CAS 1
 
diff --git a/sysdeps/loongarch/atomic-machine.h b/sysdeps/loongarch/atomic-machine.h
index 7e10309932..20cc170735 100644
--- a/sysdeps/loongarch/atomic-machine.h
+++ b/sysdeps/loongarch/atomic-machine.h
@@ -19,7 +19,6 @@
 #ifndef _LINUX_LOONGARCH_BITS_ATOMIC_H
 #define _LINUX_LOONGARCH_BITS_ATOMIC_H 1
 
-#define __HAVE_64B_ATOMICS (__loongarch_grlen >= 64)
 #define ATOMIC_EXCHANGE_USES_CAS 0
 
 #endif /* bits/atomic.h */
diff --git a/sysdeps/m68k/atomic-machine.h b/sysdeps/m68k/atomic-machine.h
index 49a65d6d99..8542affba0 100644
--- a/sysdeps/m68k/atomic-machine.h
+++ b/sysdeps/m68k/atomic-machine.h
@@ -19,9 +19,6 @@
 #define _M68K_ATOMIC_MACHINE_H	1
 
 #if defined __mc68020__ || defined __mcoldfire__
-/* If we have just non-atomic operations, we can as well make them wide.  */
-# define __HAVE_64B_ATOMICS 0 
-
 /* XXX Is this actually correct?  */
 # define ATOMIC_EXCHANGE_USES_CAS 1
 #else
diff --git a/sysdeps/microblaze/atomic-machine.h b/sysdeps/microblaze/atomic-machine.h
index d5f6f7e462..8c04235b69 100644
--- a/sysdeps/microblaze/atomic-machine.h
+++ b/sysdeps/microblaze/atomic-machine.h
@@ -18,7 +18,5 @@
 
 #include <sysdep.h>
 
-#define __HAVE_64B_ATOMICS 0
-
 /* XXX Is this actually correct?  */
 #define ATOMIC_EXCHANGE_USES_CAS 1
diff --git a/sysdeps/mips/atomic-machine.h b/sysdeps/mips/atomic-machine.h
index f19310006b..9294fb76d9 100644
--- a/sysdeps/mips/atomic-machine.h
+++ b/sysdeps/mips/atomic-machine.h
@@ -27,12 +27,6 @@
 #define MIPS_PUSH_MIPS2
 #endif
 
-#if _MIPS_SIM == _ABIO32 || _MIPS_SIM == _ABIN32
-#define __HAVE_64B_ATOMICS 0
-#else
-#define __HAVE_64B_ATOMICS 1
-#endif
-
 /* MIPS is an LL/SC machine.  However, XLP has a direct atomic exchange
    instruction which will be used by __atomic_exchange_n.  */
 #ifdef _MIPS_ARCH_XLP
diff --git a/sysdeps/or1k/atomic-machine.h b/sysdeps/or1k/atomic-machine.h
index 8dac0e4ced..51bc8a0ff4 100644
--- a/sysdeps/or1k/atomic-machine.h
+++ b/sysdeps/or1k/atomic-machine.h
@@ -19,7 +19,6 @@
 #ifndef __OR1K_ATOMIC_H_
 #define __OR1K_ATOMIC_H_
 
-#define __HAVE_64B_ATOMICS 0
 #define ATOMIC_EXCHANGE_USES_CAS 1
 
 #endif /* atomic-machine.h */
diff --git a/sysdeps/powerpc/atomic-machine.h b/sysdeps/powerpc/atomic-machine.h
index e32408a09d..988cc4f435 100644
--- a/sysdeps/powerpc/atomic-machine.h
+++ b/sysdeps/powerpc/atomic-machine.h
@@ -19,11 +19,6 @@
 #ifndef _POWERPC_ATOMIC_MACHINE_H
 #define _POWERPC_ATOMIC_MACHINE_H       1
 
-#if __WORDSIZE == 64
-# define __HAVE_64B_ATOMICS 1
-#else
-# define __HAVE_64B_ATOMICS 0
-#endif
 #define ATOMIC_EXCHANGE_USES_CAS 1
 
 /* Used on pthread_spin_{try}lock.  */
diff --git a/sysdeps/riscv/atomic-machine.h b/sysdeps/riscv/atomic-machine.h
index c5d39c1be7..5d2ad331cc 100644
--- a/sysdeps/riscv/atomic-machine.h
+++ b/sysdeps/riscv/atomic-machine.h
@@ -21,7 +21,6 @@
 
 #ifdef __riscv_atomic
 
-# define __HAVE_64B_ATOMICS (__riscv_xlen >= 64)
 # define ATOMIC_EXCHANGE_USES_CAS 0
 
 /* Miscellaneous.  */
diff --git a/sysdeps/s390/atomic-machine.h b/sysdeps/s390/atomic-machine.h
index 6f20dce802..b1646d1b07 100644
--- a/sysdeps/s390/atomic-machine.h
+++ b/sysdeps/s390/atomic-machine.h
@@ -15,10 +15,4 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#ifdef __s390x__
-# define __HAVE_64B_ATOMICS 1
-#else
-# define __HAVE_64B_ATOMICS 0
-#endif
-
 #define ATOMIC_EXCHANGE_USES_CAS 1
diff --git a/sysdeps/sh/atomic-machine.h b/sysdeps/sh/atomic-machine.h
index b4ed894bdb..b012d6f056 100644
--- a/sysdeps/sh/atomic-machine.h
+++ b/sysdeps/sh/atomic-machine.h
@@ -16,7 +16,5 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#define __HAVE_64B_ATOMICS 0
-
 /* XXX Is this actually correct?  */
 #define ATOMIC_EXCHANGE_USES_CAS 1
diff --git a/sysdeps/sparc/atomic-machine.h b/sysdeps/sparc/atomic-machine.h
index a00d2ad1d3..a16f18fe57 100644
--- a/sysdeps/sparc/atomic-machine.h
+++ b/sysdeps/sparc/atomic-machine.h
@@ -19,12 +19,6 @@
 #ifndef _ATOMIC_MACHINE_H
 #define _ATOMIC_MACHINE_H	1
 
-#ifdef __arch64__
-# define __HAVE_64B_ATOMICS          1
-#else
-# define __HAVE_64B_ATOMICS          0
-#endif
-
 /* XXX Is this actually correct?  */
 #define ATOMIC_EXCHANGE_USES_CAS     __HAVE_64B_ATOMICS
 
diff --git a/sysdeps/x86/atomic-machine.h b/sysdeps/x86/atomic-machine.h
index 0051eede70..7c2ebfcee1 100644
--- a/sysdeps/x86/atomic-machine.h
+++ b/sysdeps/x86/atomic-machine.h
@@ -19,16 +19,6 @@
 #ifndef _X86_ATOMIC_MACHINE_H
 #define _X86_ATOMIC_MACHINE_H 1
 
-#ifdef __x86_64__
-# define __HAVE_64B_ATOMICS		1
-#else
-/* Since the Pentium, i386 CPUs have supported 64-bit atomics, but the
-   i386 psABI supplement provides only 4-byte alignment for uint64_t
-   inside structs, so it is currently not possible to use 64-bit
-   atomics on this platform.  */
-# define __HAVE_64B_ATOMICS		0
-#endif
-
 #define ATOMIC_EXCHANGE_USES_CAS	0
 
 #define atomic_spin_nop() __asm ("pause")