s390/cmpxchg: Provide arch_try_cmpxchg()

Since gcc 14 flag output operands are supported also for s390.

Provide an arch_try_cmpxchg() implementation so that all existing
try_cmpxchg() variants provide slightly better code, if compiled
with gcc 14 or newer.

Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

diff --git a/arch/s390/include/asm/asm.h b/arch/s390/include/asm/asm.h
new file mode 100644 (file)
index 0000000..bea9dcf
--- /dev/null
+++ b/arch/s390/include/asm/asm.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_ASM_H
+#define _ASM_S390_ASM_H
+
+/* GCC versions before 14.2.0 may die with an ICE in some configurations. */
+#if defined(__GCC_ASM_FLAG_OUTPUTS__) && !(IS_ENABLED(CONFIG_CC_IS_GCC) && (GCC_VERSION < 140200))
+
+#define __HAVE_ASM_FLAG_OUTPUTS__
+
+#endif
+
+#endif /* _ASM_S390_ASM_H */

diff --git a/arch/s390/include/asm/cmpxchg.h b/arch/s390/include/asm/cmpxchg.h
index 587529673399017a289fe7541c49d6b2b14e0449..05f123d39bc3c687c7453046cae8badd213b8b2e 100644 (file)
--- a/arch/s390/include/asm/cmpxchg.h
+++ b/arch/s390/include/asm/cmpxchg.h
@@ -11,6 +11,7 @@
 #include <linux/mmdebug.h>
 #include <linux/types.h>
 #include <linux/bug.h>
+#include <asm/asm.h>
 
 void __xchg_called_with_bad_pointer(void);
 
@@ -174,6 +175,57 @@ static __always_inline u64 __arch_cmpxchg(u64 ptr, u64 old, u64 new, int size)
 #define arch_cmpxchg_local     arch_cmpxchg
 #define arch_cmpxchg64_local   arch_cmpxchg
 
+#ifdef __HAVE_ASM_FLAG_OUTPUTS__
+
+#define arch_try_cmpxchg(ptr, oldp, new)                               \
+({                                                                     \
+       __typeof__(ptr) __oldp = (__typeof__(ptr))(oldp);               \
+       __typeof__(*(ptr)) __old = *__oldp;                             \
+       __typeof__(*(ptr)) __new = (new);                               \
+       __typeof__(*(ptr)) __prev;                                      \
+       int __cc;                                                       \
+                                                                       \
+       switch (sizeof(*(ptr))) {                                       \
+       case 1:                                                         \
+       case 2: {                                                       \
+               __prev = arch_cmpxchg((ptr), (__old), (__new));         \
+               __cc = (__prev != __old);                               \
+               if (unlikely(__cc))                                     \
+                       *__oldp = __prev;                               \
+               break;                                                  \
+       }                                                               \
+       case 4: {                                                       \
+               asm volatile(                                           \
+                       "       cs      %[__old],%[__new],%[__ptr]\n"   \
+                       : [__old] "+d" (*__oldp),                       \
+                         [__ptr] "+Q" (*(ptr)),                        \
+                         "=@cc" (__cc)                                 \
+                       : [__new] "d" (__new)                           \
+                       : "memory");                                    \
+               break;                                                  \
+       }                                                               \
+       case 8: {                                                       \
+                asm volatile(                                          \
+                        "      csg     %[__old],%[__new],%[__ptr]\n"   \
+                        : [__old] "+d" (*__oldp),                      \
+                          [__ptr] "+QS" (*(ptr)),                      \
+                          "=@cc" (__cc)                                \
+                        : [__new] "d" (__new)                          \
+                        : "memory");                                   \
+                break;                                                 \
+       }                                                               \
+       default:                                                        \
+               __cmpxchg_called_with_bad_pointer();                    \
+       }                                                               \
+       likely(__cc == 0);                                              \
+})
+
+#define arch_try_cmpxchg64             arch_try_cmpxchg
+#define arch_try_cmpxchg_local         arch_try_cmpxchg
+#define arch_try_cmpxchg64_local       arch_try_cmpxchg
+
+#endif /* __HAVE_ASM_FLAG_OUTPUTS__ */
+
 #define system_has_cmpxchg128()                1
 
 static __always_inline u128 arch_cmpxchg128(volatile u128 *ptr, u128 old, u128 new)