x86: Use assembly instruction mnemonics instead of .byte streams in arch_hweight.h

PATCH In review Uros Bizjak 3 participants 3 messages Oct 14, 2018 – Nov 5, 2018 x86

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Uros Bizjak

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2018-10-14 20:24 UTC #0 lore raw

PATCH v2 1/1 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 <[email protected]>

---
 arch/x86/include/asm/arch_hweight.h | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

arch/x86/include/asm/arch_hweight.h +4 -8

index 34a10b2d5b73..d668e411bd32 100644
@@ -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));

Signature · 1 line

2.17.2

Borislav Petkov

maintainer

2018-10-14 20:30 UTC #1 lore raw

Quoted 8 lines · Uros Bizjak

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.

Quoted 6 lines

v2: Update commit message to emphasize removal of #defines.
Signed-off-by Uros Bizjak <[email protected]>
---
 arch/x86/include/asm/arch_hweight.h | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

Thanks.

But with one week before the merge window and this being not nearly urgent, it'll have to wait for after the merge window.

Signature · 4 lines

Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

tip-bot for Uros Bizjak

merge bot

2018-11-05 09:55 UTC #2 lore raw

[tip:x86/asm] x86: Use POPCNT mnemonics in arch_hweight.h

In reply to Uros Bizjak

x86: Use POPCNT mnemonics in arch_hweight.h

Commit-ID:  566b62a3676caed1f8c626e26066ff3ae3a38918
Gitweb:     https://git.kernel.org/tip/566b62a3676caed1f8c626e26066ff3ae3a38918
Author:     Uros Bizjak <[email protected]>
AuthorDate: Sun, 14 Oct 2018 22:23:54 +0200
Committer:  Borislav Petkov <[email protected]>
CommitDate: Mon, 5 Nov 2018 10:42:32 +0100

x86: Use POPCNT mnemonics in arch_hweight.h

Recently, the minimum required version of binutils was changed to 2.20, which supports POPCNT instruction mnemonics.

Replace the byte-wise specification of POPCNT with those proper mnemonics.

[ bp: massage commit message and remove line breaks. ]

Signed-off-by Uros Bizjak <[email protected]>

Signed-off-by Borislav Petkov <[email protected]>

CC "H. Peter Anvin" <[email protected]>

CC Ingo Molnar <[email protected]>

CC Thomas Gleixner <[email protected]>

Link http://lkml.kernel.org/r/[email protected] open here

---
 arch/x86/include/asm/arch_hweight.h | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

arch/x86/include/asm/arch_hweight.h +2 -8

index 34a10b2d5b73..fc0693569f7a 100644
@@ -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 +18,7 @@ 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 +46,7 @@ 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));