[PATCH v2] x86: Use assembly instruction mnemonics instead of .byte streams in arch_hweight.h

[PATCH v2] x86: Use assembly instruction mnemonics instead of .byte streams in arch_hweight.h

[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.

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

Signed-off-by: Uros Bizjak <ubizjak@gmail.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

Re: [PATCH v2] x86: Use assembly instruction mnemonics instead of .byte streams in arch_hweight.h

[Borislav Petkov]

On Sun, Oct 14, 2018 at 10:23:54PM +0200, Uros Bizjak wrote:
> 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@gmail.com>
> ---
>  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.

-- 
Regards/Gruss,
    Boris.

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

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

[tip-bot for Uros Bizjak]

Commit-ID:  566b62a3676caed1f8c626e26066ff3ae3a38918
Gitweb:     https://git.kernel.org/tip/566b62a3676caed1f8c626e26066ff3ae3a38918
Author:     Uros Bizjak <ubizjak@gmail.com>
AuthorDate: Sun, 14 Oct 2018 22:23:54 +0200
Committer:  Borislav Petkov <bp@suse.de>
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 <ubizjak@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Ingo Molnar <mingo@redhat.com>
CC: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181014202354.21281-1-ubizjak@gmail.com
---
 arch/x86/include/asm/arch_hweight.h | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h
index 34a10b2d5b73..fc0693569f7a 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 +18,7 @@ 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));