linux-kernel - [PATCH v2 1/3] x86/hash: fix build failure with older binutils

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Date:	Thu, 27 Feb 2014 08:47:02 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	<mingo@...e.hu>, <tglx@...utronix.de>,
	"Jan Beulich" <JBeulich@...e.com>, <hpa@...or.com>
Cc:	<davem@...emloft.net>, <dborkman@...hat.com>, <ffusco@...hat.com>,
	<tgraf@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 1/3] x86/hash: fix build failure with older binutils

Just like for other ISA extension instruction uses we should check
whether the assembler actually supports them. The fallback here simply
is to encode an instruction  with fixed operands (%eax and %ecx).

Signed-off-by: Jan Beulich <jbeulich@...e.com>
Cc: Francesco Fusco <ffusco@...hat.com>
Cc: Daniel Borkmann <dborkman@...hat.com>
Cc: Thomas Graf <tgraf@...hat.com>
Cc: David S. Miller <davem@...emloft.net>
---
 arch/x86/Makefile   |    1 +
 arch/x86/lib/hash.c |    4 ++++
 2 files changed, 5 insertions(+)

--- 3.14-rc4-x86-hash-crc32.orig/arch/x86/Makefile
+++ 3.14-rc4-x86-hash-crc32/arch/x86/Makefile
@@ -152,6 +152,7 @@ cfi-sections := $(call as-instr,.cfi_sec
 
 # does binutils support specific instructions?
 asinstr := $(call as-instr,fxsaveq (%rax),-DCONFIG_AS_FXSAVEQ=1)
+asinstr += $(call as-instr,crc32l %eax$(comma)%eax,-DCONFIG_AS_CRC32=1)
 avx_instr := $(call as-instr,vxorps %ymm0$(comma)%ymm1$(comma)%ymm2,-DCONFIG_AS_AVX=1)
 avx2_instr :=$(call as-instr,vpbroadcastb %xmm0$(comma)%ymm1,-DCONFIG_AS_AVX2=1)
 
--- 3.14-rc4-x86-hash-crc32.orig/arch/x86/lib/hash.c
+++ 3.14-rc4-x86-hash-crc32/arch/x86/lib/hash.c
@@ -39,7 +39,11 @@
 
 static inline u32 crc32_u32(u32 crc, u32 val)
 {
+#ifdef CONFIG_AS_CRC32
 	asm ("crc32l %1,%0\n" : "+r" (crc) : "rm" (val));
+#else
+	asm (".byte 0xf2, 0x0f, 0x38, 0xf1, 0xc1" : "+a" (crc) : "c" (val));
+#endif
 	return crc;
 }
 



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