linux-kernel - [PATCH 05/20] x86/asm: Always use flag output operands

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Message-ID: <9bd607a5a8b79f1349f09b4e92270aeb8acd6b43.1741988314.git.jpoimboe@kernel.org>
Date: Fri, 14 Mar 2025 14:41:18 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Uros Bizjak <ubizjak@...il.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 05/20] x86/asm: Always use flag output operands

On x86, __GCC_ASM_FLAG_OUTPUTS__ is supported starting with GCC 6.0 and
Clang 9.

Now that the GCC minimum version on x86 has been bumped to 8.1 with the
following commit:

  commit a3e8fe814ad1 ("x86/build: Raise the minimum GCC version to 8.1")

the flag output operand support can be assumed everywhere.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 arch/x86/include/asm/asm.h        |  9 ++-------
 arch/x86/include/asm/rmwcc.h      | 22 ----------------------
 tools/arch/x86/include/asm/asm.h  |  5 -----
 tools/perf/bench/find-bit-bench.c |  4 ----
 4 files changed, 2 insertions(+), 38 deletions(-)

diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 975ae7a9397e..fdebd4356860 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -131,13 +131,8 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
  * 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
+#define CC_SET(c) "\n\t/* output condition code " #c "*/\n"
+#define CC_OUT(c) "=@cc" #c
 
 #ifdef __KERNEL__
 
diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h
index 363266cbcada..a54303e3dfa1 100644
--- a/arch/x86/include/asm/rmwcc.h
+++ b/arch/x86/include/asm/rmwcc.h
@@ -6,26 +6,6 @@
 
 #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;								\
@@ -35,8 +15,6 @@ cc_label:	c = true;						\
 	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/tools/arch/x86/include/asm/asm.h b/tools/arch/x86/include/asm/asm.h
index 3ad3da9a7d97..f66cf34f6197 100644
--- a/tools/arch/x86/include/asm/asm.h
+++ b/tools/arch/x86/include/asm/asm.h
@@ -112,13 +112,8 @@
  * 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__
 
diff --git a/tools/perf/bench/find-bit-bench.c b/tools/perf/bench/find-bit-bench.c
index 7e25b0e413f6..99d36dff9d86 100644
--- a/tools/perf/bench/find-bit-bench.c
+++ b/tools/perf/bench/find-bit-bench.c
@@ -37,7 +37,6 @@ static noinline void workload(int val)
 	accumulator++;
 }
 
-#if (defined(__i386__) || defined(__x86_64__)) && defined(__GCC_ASM_FLAG_OUTPUTS__)
 static bool asm_test_bit(long nr, const unsigned long *addr)
 {
 	bool oldbit;
@@ -48,9 +47,6 @@ static bool asm_test_bit(long nr, const unsigned long *addr)
 
 	return oldbit;
 }
-#else
-#define asm_test_bit test_bit
-#endif
 
 static int do_for_each_set_bit(unsigned int num_bits)
 {
-- 
2.48.1