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[PATCH 3/5] x86/cpufeature: Get rid of the non-asm goto variant

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  [PATCH 3/5] x86/cpufeature: Get rid of the non-asm goto variant Borislav Petkov <bp@alien8.de> - 2016-01-21 19:40 +0100
    Re: [PATCH 3/5] x86/cpufeature: Get rid of the non-asm goto variant "H. Peter Anvin" <hpa@zytor.com> - 2016-01-21 20:00 +0100

#1314401 — [PATCH 3/5] x86/cpufeature: Get rid of the non-asm goto variant

From: Borislav Petkov <bp@suse.de>

I can simply quote hpa from the mail:

"Get rid of the non-asm goto variant and just fall back to dynamic if
asm goto is unavailable. It doesn't make any sense, really, if it is
supposed to be safe, and by now the asm goto-capable gcc is in more wide
use. (Originally the gcc 3.x fallback to pure dynamic didn't exist,
either.)"

Booy, am I lazy.

Signed-off-by: Borislav Petkov <bp@suse.de>
Suggested-by: "H. Peter Anvin" <hpa@zytor.com>
---
 arch/x86/include/asm/cpufeature.h | 38 +-------------------------------------
 1 file changed, 1 insertion(+), 37 deletions(-)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 2b0abb241205..e4759223f82c 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -174,43 +174,7 @@ static __always_inline __pure bool _static_cpu_has(u16 bit)
 	t_dynamic:
 		return __static_cpu_has(bit);
 #else
-		u8 flag;
-		/* Open-coded due to __stringify() in ALTERNATIVE() */
-		asm volatile("1: movb $2,%0\n"
-			     "2:\n"
-			     ".section .altinstructions,\"a\"\n"
-			     " .long 1b - .\n"		/* src offset */
-			     " .long 3f - .\n"		/* repl offset */
-			     " .word %P2\n"		/* always replace */
-			     " .byte 2b - 1b\n"		/* source len */
-			     " .byte 4f - 3f\n"		/* replacement len */
-			     " .byte 0\n"		/* pad len */
-			     ".previous\n"
-			     ".section .discard,\"aw\",@progbits\n"
-			     " .byte 0xff + (4f-3f) - (2b-1b)\n" /* size check */
-			     ".previous\n"
-			     ".section .altinstr_replacement,\"ax\"\n"
-			     "3: movb $0,%0\n"
-			     "4:\n"
-			     ".previous\n"
-			     ".section .altinstructions,\"a\"\n"
-			     " .long 1b - .\n"		/* src offset */
-			     " .long 5f - .\n"		/* repl offset */
-			     " .word %P1\n"		/* feature bit */
-			     " .byte 4b - 3b\n"		/* src len */
-			     " .byte 6f - 5f\n"		/* repl len */
-			     " .byte 0\n"		/* pad len */
-			     ".previous\n"
-			     ".section .discard,\"aw\",@progbits\n"
-			     " .byte 0xff + (6f-5f) - (4b-3b)\n" /* size check */
-			     ".previous\n"
-			     ".section .altinstr_replacement,\"ax\"\n"
-			     "5: movb $1,%0\n"
-			     "6:\n"
-			     ".previous\n"
-			     : "=qm" (flag)
-			     : "i" (bit), "i" (X86_FEATURE_ALWAYS));
-		return (flag == 2 ? __static_cpu_has(bit) : flag);
+		return boot_cpu_has(bit);
 #endif /* CC_HAVE_ASM_GOTO */
 }
 
-- 
2.3.5

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#1314418

On 01/21/16 10:34, Borislav Petkov wrote:
> From: Borislav Petkov <bp@suse.de>
> 
> I can simply quote hpa from the mail:
> 
> "Get rid of the non-asm goto variant and just fall back to dynamic if
> asm goto is unavailable. It doesn't make any sense, really, if it is
> supposed to be safe, and by now the asm goto-capable gcc is in more wide
> use. (Originally the gcc 3.x fallback to pure dynamic didn't exist,
> either.)"
> 
> Booy, am I lazy.
> 

Laughed-at-by: H. Peter Anvin <hpa@zytor.com>

	;)

	-hpa

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