Commit 6041b57c authored by Joerg Roedel's avatar Joerg Roedel Committed by Linus Torvalds
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i386: work around miscompilation of alternatives code 



A recent change makes my Dell 1501 hang on boot.  It's an AMD MK-36.  I use
an x86_64 kernel.  It is 100% reproducible.

I debugged this problem a bit and my compiler[1]interprets the =A constraint
as %rax instead of %edx:%eax on x86_64 which causes the problem.  The appended
patch provides a workaround for this and fixed the hang on my machine.

[1] gcc version 4.1.3 20070429 (prerelease) (Debian 4.1.2-5)

Signed-off-by: default avatarJoerg Roedel <joerg.roedel@amd.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Benny Halevy <bhalevy@panasas.com>
Cc: Pete Zaitcev <zaitcev@redhat.com>
Cc: "Joerg Roedel" <joerg.roedel@amd.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 129a84de

include/asm-i386/alternative.h

+6 −0
Original line number Diff line number Diff line
@@ -97,6 +97,12 @@ static inline void alternatives_smp_switch(int smp) {} 
		      "663:\n\t" newinstr "\n664:\n"   /* replacement */ \

		      ".previous" : output : [feat] "i" (feature), ##input)



/*

 * use this macro(s) if you need more than one output parameter

 * in alternative_io

 */

#define ASM_OUTPUT2(a, b) a, b



/*

 * Alternative inline assembly for SMP.

 *

include/asm-i386/tsc.h

+4 −2
Original line number Diff line number Diff line
@@ -35,14 +35,16 @@ static inline cycles_t get_cycles(void) 
static __always_inline cycles_t get_cycles_sync(void)

{

	unsigned long long ret;

	unsigned eax;

	unsigned eax, edx;



	/*

  	 * Use RDTSCP if possible; it is guaranteed to be synchronous

 	 * and doesn't cause a VMEXIT on Hypervisors

	 */

	alternative_io(ASM_NOP3, ".byte 0x0f,0x01,0xf9", X86_FEATURE_RDTSCP,

			 	 "=A" (ret), "0" (0ULL) : "ecx", "memory");

		       ASM_OUTPUT2("=a" (eax), "=d" (edx)),

		       "a" (0U), "d" (0U) : "ecx", "memory");

	ret = (((unsigned long long)edx) << 32) | ((unsigned long long)eax);

	if (ret)

		return ret;

include/asm-x86_64/alternative.h

+6 −0
Original line number Diff line number Diff line
@@ -102,6 +102,12 @@ static inline void alternatives_smp_switch(int smp) {} 
		      "663:\n\t" newinstr "\n664:\n"   /* replacement */ \

		      ".previous" : output : [feat] "i" (feature), ##input)



/*

 * use this macro(s) if you need more than one output parameter

 * in alternative_io

 */

#define ASM_OUTPUT2(a, b) a, b



/*

 * Alternative inline assembly for SMP.

 *

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