x86/asm: Remove code depending on __GCC_ASM_FLAG_OUTPUTS__

ubizjak · bp3tk0v · commit c6c973dbfa5e · 2025-09-08T15:38:06.000+02:00
The minimum supported GCC version is 8.1, which supports flag output operands and always defines __GCC_ASM_FLAG_OUTPUTS__ macro. Remove code depending on __GCC_ASM_FLAG_OUTPUTS__ and use the "=@ccCOND" flag output operand directly. Use the equivalent "=@ccz" instead of "=@cce" flag output operand for CMPXCHG8B and CMPXCHG16B instructions. These instructions set a single flag bit - the Zero flag - and "=@ccz" is used to distinguish the CC user from comparison instructions, where set ZERO flag indeed means that the values are equal. Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Link: https://lore.kernel.org/r/20250905121723.GCaLrU04lP2A50PT-B@fat_crate.local
diff --git a/arch/x86/boot/bitops.h b/arch/x86/boot/bitops.h
@@ -27,7 +27,7 @@ static inline bool variable_test_bit(int nr, const void *addr)
 	bool v;
 	const u32 *p = addr;
 
-	asm("btl %2,%1" CC_SET(c) : CC_OUT(c) (v) : "m" (*p), "Ir" (nr));
+	asm("btl %2,%1" : "=@ccc" (v) : "m" (*p), "Ir" (nr));
 	return v;
 }
 
diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
@@ -155,15 +155,15 @@ static inline void wrgs32(u32 v, addr_t addr)
 static inline bool memcmp_fs(const void *s1, addr_t s2, size_t len)
 {
 	bool diff;
-	asm volatile("fs repe cmpsb" CC_SET(nz)
-		     : CC_OUT(nz) (diff), "+D" (s1), "+S" (s2), "+c" (len));
+	asm volatile("fs repe cmpsb"
+		     : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
 	return diff;
 }
 static inline bool memcmp_gs(const void *s1, addr_t s2, size_t len)
 {
 	bool diff;
-	asm volatile("gs repe cmpsb" CC_SET(nz)
-		     : CC_OUT(nz) (diff), "+D" (s1), "+S" (s2), "+c" (len));
+	asm volatile("gs repe cmpsb"
+		     : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
 	return diff;
 }
 
diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
@@ -32,8 +32,8 @@
 int memcmp(const void *s1, const void *s2, size_t len)
 {
 	bool diff;
-	asm("repe cmpsb" CC_SET(nz)
-	    : CC_OUT(nz) (diff), "+D" (s1), "+S" (s2), "+c" (len));
+	asm("repe cmpsb"
+	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
 	return diff;
 }
 
diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h
@@ -23,8 +23,7 @@ static inline bool __must_check rdrand_long(unsigned long *v)
 	unsigned int retry = RDRAND_RETRY_LOOPS;
 	do {
 		asm volatile("rdrand %[out]"
-			     CC_SET(c)
-			     : CC_OUT(c) (ok), [out] "=r" (*v));
+			     : "=@ccc" (ok), [out] "=r" (*v));
 		if (ok)
 			return true;
 	} while (--retry);
@@ -35,8 +34,7 @@ static inline bool __must_check rdseed_long(unsigned long *v)
 {
 	bool ok;
 	asm volatile("rdseed %[out]"
-		     CC_SET(c)
-		     : CC_OUT(c) (ok), [out] "=r" (*v));
+		     : "=@ccc" (ok), [out] "=r" (*v));
 	return ok;
 }
 
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
@@ -122,18 +122,6 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
 }
 #endif
 
-/*
- * Macros to generate condition code outputs from inline assembly,
- * The output operand must be type "bool".
- */
-#ifdef __GCC_ASM_FLAG_OUTPUTS__
-# define CC_SET(c) "\n\t/* output condition code " #c "*/\n"
-# define CC_OUT(c) "=@cc" #c
-#else
-# define CC_SET(c) "\n\tset" #c " %[_cc_" #c "]\n"
-# define CC_OUT(c) [_cc_ ## c] "=qm"
-#endif
-
 #ifdef __KERNEL__
 
 # include <asm/extable_fixup_types.h>
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
@@ -99,8 +99,7 @@ static __always_inline bool arch_xor_unlock_is_negative_byte(unsigned long mask,
 {
 	bool negative;
 	asm_inline volatile(LOCK_PREFIX "xorb %2,%1"
-		CC_SET(s)
-		: CC_OUT(s) (negative), WBYTE_ADDR(addr)
+		: "=@ccs" (negative), WBYTE_ADDR(addr)
 		: "iq" ((char)mask) : "memory");
 	return negative;
 }
@@ -149,8 +148,7 @@ arch___test_and_set_bit(unsigned long nr, volatile unsigned long *addr)
 	bool oldbit;
 
 	asm(__ASM_SIZE(bts) " %2,%1"
-	    CC_SET(c)
-	    : CC_OUT(c) (oldbit)
+	    : "=@ccc" (oldbit)
 	    : ADDR, "Ir" (nr) : "memory");
 	return oldbit;
 }
@@ -175,8 +173,7 @@ arch___test_and_clear_bit(unsigned long nr, volatile unsigned long *addr)
 	bool oldbit;
 
 	asm volatile(__ASM_SIZE(btr) " %2,%1"
-		     CC_SET(c)
-		     : CC_OUT(c) (oldbit)
+		     : "=@ccc" (oldbit)
 		     : ADDR, "Ir" (nr) : "memory");
 	return oldbit;
 }
@@ -187,8 +184,7 @@ arch___test_and_change_bit(unsigned long nr, volatile unsigned long *addr)
 	bool oldbit;
 
 	asm volatile(__ASM_SIZE(btc) " %2,%1"
-		     CC_SET(c)
-		     : CC_OUT(c) (oldbit)
+		     : "=@ccc" (oldbit)
 		     : ADDR, "Ir" (nr) : "memory");
 
 	return oldbit;
@@ -211,8 +207,7 @@ static __always_inline bool constant_test_bit_acquire(long nr, const volatile un
 	bool oldbit;
 
 	asm volatile("testb %2,%1"
-		     CC_SET(nz)
-		     : CC_OUT(nz) (oldbit)
+		     : "=@ccnz" (oldbit)
 		     : "m" (((unsigned char *)addr)[nr >> 3]),
 		       "i" (1 << (nr & 7))
 		     :"memory");
@@ -225,8 +220,7 @@ static __always_inline bool variable_test_bit(long nr, volatile const unsigned l
 	bool oldbit;
 
 	asm volatile(__ASM_SIZE(bt) " %2,%1"
-		     CC_SET(c)
-		     : CC_OUT(c) (oldbit)
+		     : "=@ccc" (oldbit)
 		     : "m" (*(unsigned long *)addr), "Ir" (nr) : "memory");
 
 	return oldbit;
diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
@@ -166,8 +166,7 @@ extern void __add_wrong_size(void)
 	{								\
 		volatile u8 *__ptr = (volatile u8 *)(_ptr);		\
 		asm_inline volatile(lock "cmpxchgb %[new], %[ptr]"	\
-			     CC_SET(z)					\
-			     : CC_OUT(z) (success),			\
+			     : "=@ccz" (success),			\
 			       [ptr] "+m" (*__ptr),			\
 			       [old] "+a" (__old)			\
 			     : [new] "q" (__new)			\
@@ -178,8 +177,7 @@ extern void __add_wrong_size(void)
 	{								\
 		volatile u16 *__ptr = (volatile u16 *)(_ptr);		\
 		asm_inline volatile(lock "cmpxchgw %[new], %[ptr]"	\
-			     CC_SET(z)					\
-			     : CC_OUT(z) (success),			\
+			     : "=@ccz" (success),			\
 			       [ptr] "+m" (*__ptr),			\
 			       [old] "+a" (__old)			\
 			     : [new] "r" (__new)			\
@@ -190,8 +188,7 @@ extern void __add_wrong_size(void)
 	{								\
 		volatile u32 *__ptr = (volatile u32 *)(_ptr);		\
 		asm_inline volatile(lock "cmpxchgl %[new], %[ptr]"	\
-			     CC_SET(z)					\
-			     : CC_OUT(z) (success),			\
+			     : "=@ccz" (success),			\
 			       [ptr] "+m" (*__ptr),			\
 			       [old] "+a" (__old)			\
 			     : [new] "r" (__new)			\
@@ -202,8 +199,7 @@ extern void __add_wrong_size(void)
 	{								\
 		volatile u64 *__ptr = (volatile u64 *)(_ptr);		\
 		asm_inline volatile(lock "cmpxchgq %[new], %[ptr]"	\
-			     CC_SET(z)					\
-			     : CC_OUT(z) (success),			\
+			     : "=@ccz" (success),			\
 			       [ptr] "+m" (*__ptr),			\
 			       [old] "+a" (__old)			\
 			     : [new] "r" (__new)			\
diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
@@ -46,8 +46,7 @@ static __always_inline u64 __cmpxchg64_local(volatile u64 *ptr, u64 old, u64 new
 	bool ret;							\
 									\
 	asm_inline volatile(_lock "cmpxchg8b %[ptr]"			\
-		     CC_SET(e)						\
-		     : CC_OUT(e) (ret),					\
+		     : "=@ccz" (ret),					\
 		       [ptr] "+m" (*(_ptr)),				\
 		       "+a" (o.low), "+d" (o.high)			\
 		     : "b" (n.low), "c" (n.high)			\
@@ -125,8 +124,7 @@ static __always_inline u64 arch_cmpxchg64_local(volatile u64 *ptr, u64 old, u64
 		ALTERNATIVE(_lock_loc					\
 			    "call cmpxchg8b_emu",			\
 			    _lock "cmpxchg8b %a[ptr]", X86_FEATURE_CX8) \
-		CC_SET(e)						\
-		: ALT_OUTPUT_SP(CC_OUT(e) (ret),			\
+		: ALT_OUTPUT_SP("=@ccz" (ret),				\
 				"+a" (o.low), "+d" (o.high))		\
 		: "b" (n.low), "c" (n.high),				\
 		  [ptr] "S" (_ptr)					\
diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
@@ -66,8 +66,7 @@ static __always_inline u128 arch_cmpxchg128_local(volatile u128 *ptr, u128 old,
 	bool ret;							\
 									\
 	asm_inline volatile(_lock "cmpxchg16b %[ptr]"			\
-		     CC_SET(e)						\
-		     : CC_OUT(e) (ret),					\
+		     : "=@ccz" (ret),					\
 		       [ptr] "+m" (*(_ptr)),				\
 		       "+a" (o.low), "+d" (o.high)			\
 		     : "b" (n.low), "c" (n.high)			\
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
@@ -309,8 +309,7 @@ do {									\
 									\
 	asm qual (__pcpu_op_##size("cmpxchg") "%[nval], "		\
 		  __percpu_arg([var])					\
-		  CC_SET(z)						\
-		  : CC_OUT(z) (success),				\
+		  : "=@ccz" (success),					\
 		    [oval] "+a" (pco_old__),				\
 		    [var] "+m" (__my_cpu_var(_var))			\
 		  : [nval] __pcpu_reg_##size(, pco_new__)		\
@@ -367,8 +366,7 @@ do {									\
 	asm_inline qual (						\
 		ALTERNATIVE("call this_cpu_cmpxchg8b_emu",		\
 			    "cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
-		CC_SET(z)						\
-		: ALT_OUTPUT_SP(CC_OUT(z) (success),			\
+		: ALT_OUTPUT_SP("=@ccz" (success),			\
 				[var] "+m" (__my_cpu_var(_var)),	\
 				"+a" (old__.low), "+d" (old__.high))	\
 		: "b" (new__.low), "c" (new__.high),			\
@@ -436,8 +434,7 @@ do {									\
 	asm_inline qual (						\
 		ALTERNATIVE("call this_cpu_cmpxchg16b_emu",		\
 			    "cmpxchg16b " __percpu_arg([var]), X86_FEATURE_CX16) \
-		CC_SET(z)						\
-		: ALT_OUTPUT_SP(CC_OUT(z) (success),			\
+		: ALT_OUTPUT_SP("=@ccz" (success),			\
 				[var] "+m" (__my_cpu_var(_var)),	\
 				"+a" (old__.low), "+d" (old__.high))	\
 		: "b" (new__.low), "c" (new__.high),			\
@@ -585,8 +582,7 @@ do {									\
 	bool oldbit;							\
 									\
 	asm volatile("btl %[nr], " __percpu_arg([var])			\
-		     CC_SET(c)						\
-		     : CC_OUT(c) (oldbit)				\
+		     : "=@ccc" (oldbit)					\
 		     : [var] "m" (__my_cpu_var(_var)),			\
 		       [nr] "rI" (_nr));				\
 	oldbit;								\
diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h
@@ -6,37 +6,15 @@
 
 #define __CLOBBERS_MEM(clb...)	"memory", ## clb
 
-#ifndef __GCC_ASM_FLAG_OUTPUTS__
-
-/* Use asm goto */
-
-#define __GEN_RMWcc(fullop, _var, cc, clobbers, ...)			\
-({									\
-	bool c = false;							\
-	asm goto (fullop "; j" #cc " %l[cc_label]"		\
-			: : [var] "m" (_var), ## __VA_ARGS__		\
-			: clobbers : cc_label);				\
-	if (0) {							\
-cc_label:	c = true;						\
-	}								\
-	c;								\
-})
-
-#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) */
-
-/* Use flags output or a set instruction */
-
 #define __GEN_RMWcc(fullop, _var, cc, clobbers, ...)			\
 ({									\
 	bool c;								\
-	asm_inline volatile (fullop CC_SET(cc)				\
-			: [var] "+m" (_var), CC_OUT(cc) (c)		\
+	asm_inline volatile (fullop					\
+			: [var] "+m" (_var), "=@cc" #cc (c)		\
 			: __VA_ARGS__ : clobbers);			\
 	c;								\
 })
 
-#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) */
-
 #define GEN_UNARY_RMWcc_4(op, var, cc, arg0)				\
 	__GEN_RMWcc(op " " arg0, var, cc, __CLOBBERS_MEM())
 
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
@@ -491,8 +491,7 @@ static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate)
 
 	/* "pvalidate" mnemonic support in binutils 2.36 and newer */
 	asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFF\n\t"
-		     CC_SET(c)
-		     : CC_OUT(c) (no_rmpupdate), "=a"(rc)
+		     : "=@ccc"(no_rmpupdate), "=a"(rc)
 		     : "a"(vaddr), "c"(rmp_psize), "d"(validate)
 		     : "memory", "cc");
 
diff --git a/arch/x86/include/asm/signal.h b/arch/x86/include/asm/signal.h
@@ -83,8 +83,7 @@ static inline int __const_sigismember(sigset_t *set, int _sig)
 static inline int __gen_sigismember(sigset_t *set, int _sig)
 {
 	bool ret;
-	asm("btl %2,%1" CC_SET(c)
-	    : CC_OUT(c) (ret) : "m"(*set), "Ir"(_sig-1));
+	asm("btl %2,%1" : "=@ccc"(ret) : "m"(*set), "Ir"(_sig-1));
 	return ret;
 }
 
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
@@ -284,8 +284,7 @@ static inline int enqcmds(void __iomem *dst, const void *src)
 	 * See movdir64b()'s comment on operand specification.
 	 */
 	asm volatile(".byte 0xf3, 0x0f, 0x38, 0xf8, 0x02, 0x66, 0x90"
-		     CC_SET(z)
-		     : CC_OUT(z) (zf), "+m" (*__dst)
+		     : "=@ccz" (zf), "+m" (*__dst)
 		     : "m" (*__src), "a" (__dst), "d" (__src));
 
 	/* Submission failure is indicated via EFLAGS.ZF=1 */
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
@@ -378,7 +378,7 @@ do {									\
 	asm_goto_output("\n"						\
 		     "1: " LOCK_PREFIX "cmpxchg"itype" %[new], %[ptr]\n"\
 		     _ASM_EXTABLE_UA(1b, %l[label])			\
-		     : CC_OUT(z) (success),				\
+		     : "=@ccz" (success),				\
 		       [ptr] "+m" (*_ptr),				\
 		       [old] "+a" (__old)				\
 		     : [new] ltype (__new)				\
@@ -397,7 +397,7 @@ do {									\
 	asm_goto_output("\n"						\
 		     "1: " LOCK_PREFIX "cmpxchg8b %[ptr]\n"		\
 		     _ASM_EXTABLE_UA(1b, %l[label])			\
-		     : CC_OUT(z) (success),				\
+		     : "=@ccz" (success),				\
 		       "+A" (__old),					\
 		       [ptr] "+m" (*_ptr)				\
 		     : "b" ((u32)__new),				\
@@ -417,11 +417,10 @@ do {									\
 	__typeof__(*(_ptr)) __new = (_new);				\
 	asm volatile("\n"						\
 		     "1: " LOCK_PREFIX "cmpxchg"itype" %[new], %[ptr]\n"\
-		     CC_SET(z)						\
 		     "2:\n"						\
 		     _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_EFAULT_REG,	\
 					   %[errout])			\
-		     : CC_OUT(z) (success),				\
+		     : "=@ccz" (success),				\
 		       [errout] "+r" (__err),				\
 		       [ptr] "+m" (*_ptr),				\
 		       [old] "+a" (__old)				\
diff --git a/tools/arch/x86/include/asm/asm.h b/tools/arch/x86/include/asm/asm.h
@@ -108,18 +108,6 @@
 
 #endif
 
-/*
- * Macros to generate condition code outputs from inline assembly,
- * The output operand must be type "bool".
- */
-#ifdef __GCC_ASM_FLAG_OUTPUTS__
-# define CC_SET(c) "\n\t/* output condition code " #c "*/\n"
-# define CC_OUT(c) "=@cc" #c
-#else
-# define CC_SET(c) "\n\tset" #c " %[_cc_" #c "]\n"
-# define CC_OUT(c) [_cc_ ## c] "=qm"
-#endif
-
 #ifdef __KERNEL__
 
 /* Exception table entry */
diff --git a/tools/perf/bench/find-bit-bench.c b/tools/perf/bench/find-bit-bench.c
@@ -37,7 +37,7 @@ static noinline void workload(int val)
 	accumulator++;
 }
 
-#if (defined(__i386__) || defined(__x86_64__)) && defined(__GCC_ASM_FLAG_OUTPUTS__)
+#if defined(__i386__) || defined(__x86_64__)
 static bool asm_test_bit(long nr, const unsigned long *addr)
 {
 	bool oldbit;

Original file line number	Diff line number	Diff line change
`@@ -27,7 +27,7 @@ static inline bool variable_test_bit(int nr, const void *addr)`
`27`	`27`	`bool v;`
`28`	`28`	`const u32 *p = addr;`
`29`	`29`
`30`		`- asm("btl %2,%1" CC_SET(c) : CC_OUT(c) (v) : "m" (*p), "Ir" (nr));`
	`30`	`+ asm("btl %2,%1" : "=@ccc" (v) : "m" (*p), "Ir" (nr));`
`31`	`31`	`return v;`
`32`	`32`	`}`
`33`	`33`
Original file line number	Diff line number	Diff line change
`@@ -155,15 +155,15 @@ static inline void wrgs32(u32 v, addr_t addr)`
`155`	`155`	`static inline bool memcmp_fs(const void *s1, addr_t s2, size_t len)`
`156`	`156`	`{`
`157`	`157`	`bool diff;`
`158`		`- asm volatile("fs repe cmpsb" CC_SET(nz)`
`159`		`- : CC_OUT(nz) (diff), "+D" (s1), "+S" (s2), "+c" (len));`
	`158`	`+ asm volatile("fs repe cmpsb"`
	`159`	`+ : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));`
`160`	`160`	`return diff;`
`161`	`161`	`}`
`162`	`162`	`static inline bool memcmp_gs(const void *s1, addr_t s2, size_t len)`
`163`	`163`	`{`
`164`	`164`	`bool diff;`
`165`		`- asm volatile("gs repe cmpsb" CC_SET(nz)`
`166`		`- : CC_OUT(nz) (diff), "+D" (s1), "+S" (s2), "+c" (len));`
	`165`	`+ asm volatile("gs repe cmpsb"`
	`166`	`+ : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));`
`167`	`167`	`return diff;`
`168`	`168`	`}`
`169`	`169`
Original file line number	Diff line number	Diff line change
`@@ -32,8 +32,8 @@`
`32`	`32`	`int memcmp(const void s1, const void s2, size_t len)`
`33`	`33`	`{`
`34`	`34`	`bool diff;`
`35`		`- asm("repe cmpsb" CC_SET(nz)`
`36`		`- : CC_OUT(nz) (diff), "+D" (s1), "+S" (s2), "+c" (len));`
	`35`	`+ asm("repe cmpsb"`
	`36`	`+ : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));`
`37`	`37`	`return diff;`
`38`	`38`	`}`
`39`	`39`