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x86: Add memory modify constraints to xchg() and cmpxchg()
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xchg() and cmpxchg() modify their memory operands, not merely read
them.  For some versions of gcc the "memory" clobber has apparently
dealt with the situation, but not for all.

Originally-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Glauber Costa <glommer@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Peter Palfrader <peter@palfrader.org>
Cc: Greg KH <gregkh@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Zachary Amsden <zamsden@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: <stable@kernel.org>
LKML-Reference: <4C4F7277.8050306@zytor.com>
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H. Peter Anvin committed Jul 28, 2010
1 parent fc0f5ac commit 113fc5a
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Showing 2 changed files with 54 additions and 54 deletions.
68 changes: 34 additions & 34 deletions arch/x86/include/asm/cmpxchg_32.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -27,20 +27,20 @@ struct __xchg_dummy {
switch (size) { \
case 1: \
asm volatile("xchgb %b0,%1" \
: "=q" (__x) \
: "m" (*__xg(ptr)), "0" (__x) \
: "=q" (__x), "+m" (*__xg(ptr)) \
: "0" (__x) \
: "memory"); \
break; \
case 2: \
asm volatile("xchgw %w0,%1" \
: "=r" (__x) \
: "m" (*__xg(ptr)), "0" (__x) \
: "=r" (__x), "+m" (*__xg(ptr)) \
: "0" (__x) \
: "memory"); \
break; \
case 4: \
asm volatile("xchgl %0,%1" \
: "=r" (__x) \
: "m" (*__xg(ptr)), "0" (__x) \
: "=r" (__x), "+m" (*__xg(ptr)) \
: "0" (__x) \
: "memory"); \
break; \
default: \
Expand Down Expand Up @@ -70,14 +70,14 @@ static inline void __set_64bit(unsigned long long *ptr,
unsigned int low, unsigned int high)
{
asm volatile("\n1:\t"
"movl (%0), %%eax\n\t"
"movl 4(%0), %%edx\n\t"
LOCK_PREFIX "cmpxchg8b (%0)\n\t"
"movl (%1), %%eax\n\t"
"movl 4(%1), %%edx\n\t"
LOCK_PREFIX "cmpxchg8b (%1)\n\t"
"jnz 1b"
: /* no outputs */
: "D"(ptr),
"b"(low),
"c"(high)
: "=m" (*ptr)
: "D" (ptr),
"b" (low),
"c" (high)
: "ax", "dx", "memory");
}

Expand Down Expand Up @@ -121,21 +121,21 @@ extern void __cmpxchg_wrong_size(void);
__typeof__(*(ptr)) __new = (new); \
switch (size) { \
case 1: \
asm volatile(lock "cmpxchgb %b1,%2" \
: "=a"(__ret) \
: "q"(__new), "m"(*__xg(ptr)), "0"(__old) \
asm volatile(lock "cmpxchgb %b2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
: "q" (__new), "0" (__old) \
: "memory"); \
break; \
case 2: \
asm volatile(lock "cmpxchgw %w1,%2" \
: "=a"(__ret) \
: "r"(__new), "m"(*__xg(ptr)), "0"(__old) \
asm volatile(lock "cmpxchgw %w2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
case 4: \
asm volatile(lock "cmpxchgl %1,%2" \
: "=a"(__ret) \
: "r"(__new), "m"(*__xg(ptr)), "0"(__old) \
asm volatile(lock "cmpxchgl %2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
default: \
Expand Down Expand Up @@ -180,12 +180,12 @@ static inline unsigned long long __cmpxchg64(volatile void *ptr,
unsigned long long new)
{
unsigned long long prev;
asm volatile(LOCK_PREFIX "cmpxchg8b %3"
: "=A"(prev)
: "b"((unsigned long)new),
"c"((unsigned long)(new >> 32)),
"m"(*__xg(ptr)),
"0"(old)
asm volatile(LOCK_PREFIX "cmpxchg8b %1"
: "=A" (prev),
"+m" (*__xg(ptr))
: "b" ((unsigned long)new),
"c" ((unsigned long)(new >> 32)),
"0" (old)
: "memory");
return prev;
}
Expand All @@ -195,12 +195,12 @@ static inline unsigned long long __cmpxchg64_local(volatile void *ptr,
unsigned long long new)
{
unsigned long long prev;
asm volatile("cmpxchg8b %3"
: "=A"(prev)
: "b"((unsigned long)new),
"c"((unsigned long)(new >> 32)),
"m"(*__xg(ptr)),
"0"(old)
asm volatile("cmpxchg8b %1"
: "=A" (prev),
"+m" (*__xg(ptr))
: "b" ((unsigned long)new),
"c" ((unsigned long)(new >> 32)),
"0" (old)
: "memory");
return prev;
}
Expand Down
40 changes: 20 additions & 20 deletions arch/x86/include/asm/cmpxchg_64.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -26,26 +26,26 @@ extern void __cmpxchg_wrong_size(void);
switch (size) { \
case 1: \
asm volatile("xchgb %b0,%1" \
: "=q" (__x) \
: "m" (*__xg(ptr)), "0" (__x) \
: "=q" (__x), "+m" (*__xg(ptr)) \
: "0" (__x) \
: "memory"); \
break; \
case 2: \
asm volatile("xchgw %w0,%1" \
: "=r" (__x) \
: "m" (*__xg(ptr)), "0" (__x) \
: "=r" (__x), "+m" (*__xg(ptr)) \
: "0" (__x) \
: "memory"); \
break; \
case 4: \
asm volatile("xchgl %k0,%1" \
: "=r" (__x) \
: "m" (*__xg(ptr)), "0" (__x) \
: "=r" (__x), "+m" (*__xg(ptr)) \
: "0" (__x) \
: "memory"); \
break; \
case 8: \
asm volatile("xchgq %0,%1" \
: "=r" (__x) \
: "m" (*__xg(ptr)), "0" (__x) \
: "=r" (__x), "+m" (*__xg(ptr)) \
: "0" (__x) \
: "memory"); \
break; \
default: \
Expand All @@ -71,27 +71,27 @@ extern void __cmpxchg_wrong_size(void);
__typeof__(*(ptr)) __new = (new); \
switch (size) { \
case 1: \
asm volatile(lock "cmpxchgb %b1,%2" \
: "=a"(__ret) \
: "q"(__new), "m"(*__xg(ptr)), "0"(__old) \
asm volatile(lock "cmpxchgb %b2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
: "q" (__new), "0" (__old) \
: "memory"); \
break; \
case 2: \
asm volatile(lock "cmpxchgw %w1,%2" \
: "=a"(__ret) \
: "r"(__new), "m"(*__xg(ptr)), "0"(__old) \
asm volatile(lock "cmpxchgw %w2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
case 4: \
asm volatile(lock "cmpxchgl %k1,%2" \
: "=a"(__ret) \
: "r"(__new), "m"(*__xg(ptr)), "0"(__old) \
asm volatile(lock "cmpxchgl %k2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
case 8: \
asm volatile(lock "cmpxchgq %1,%2" \
: "=a"(__ret) \
: "r"(__new), "m"(*__xg(ptr)), "0"(__old) \
asm volatile(lock "cmpxchgq %2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
default: \
Expand Down

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