linux-kernel - [PATCH v2] x86: Use assembly instruction mnemonics instead of .byte streams in arch

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Message-Id: <20181014202354.21281-1-ubizjak@gmail.com>
Date:   Sun, 14 Oct 2018 22:23:54 +0200
From:   Uros Bizjak <ubizjak@...il.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org, bp@...en8.de
Cc:     Uros Bizjak <ubizjak@...il.com>
Subject: [PATCH v2] x86: Use assembly instruction mnemonics instead of .byte streams in arch_hweight.h

Recently the minimum required version of binutils was changed to 2.20,
which supports popcnt instruction mnemonics. The patch removes
corresponding #defines that implement popcnt instructions using target-dependant
.byte streams and uses unified instruction mnemonics instead.

Tested by building x86_64 and i386 version of the kernel and comparing
objdump dumps of the pathced and unpatched vmlinux.o. They were the same.

v2: Update commit message to emphasize removal of #defines.

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
 arch/x86/include/asm/arch_hweight.h | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h
index 34a10b2d5b73..d668e411bd32 100644
--- a/arch/x86/include/asm/arch_hweight.h
+++ b/arch/x86/include/asm/arch_hweight.h
@@ -5,15 +5,9 @@
 #include <asm/cpufeatures.h>
 
 #ifdef CONFIG_64BIT
-/* popcnt %edi, %eax */
-#define POPCNT32 ".byte 0xf3,0x0f,0xb8,0xc7"
-/* popcnt %rdi, %rax */
-#define POPCNT64 ".byte 0xf3,0x48,0x0f,0xb8,0xc7"
 #define REG_IN "D"
 #define REG_OUT "a"
 #else
-/* popcnt %eax, %eax */
-#define POPCNT32 ".byte 0xf3,0x0f,0xb8,0xc0"
 #define REG_IN "a"
 #define REG_OUT "a"
 #endif
@@ -24,7 +18,8 @@ static __always_inline unsigned int __arch_hweight32(unsigned int w)
 {
 	unsigned int res;
 
-	asm (ALTERNATIVE("call __sw_hweight32", POPCNT32, X86_FEATURE_POPCNT)
+	asm (ALTERNATIVE("call __sw_hweight32",
+			 "popcntl %1, %0", X86_FEATURE_POPCNT)
 			 : "="REG_OUT (res)
 			 : REG_IN (w));
 
@@ -52,7 +47,8 @@ static __always_inline unsigned long __arch_hweight64(__u64 w)
 {
 	unsigned long res;
 
-	asm (ALTERNATIVE("call __sw_hweight64", POPCNT64, X86_FEATURE_POPCNT)
+	asm (ALTERNATIVE("call __sw_hweight64",
+			 "popcntq %1, %0", X86_FEATURE_POPCNT)
 			 : "="REG_OUT (res)
 			 : REG_IN (w));
 
-- 
2.17.2