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
......@@ -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.
*
......
......@@ -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;
......
......@@ -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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