Skip to content

Commit

Permalink
x86, asm: Clean up and simplify <asm/cmpxchg.h>
Browse files Browse the repository at this point in the history 
Remove the __xg() hack to create a memory barrier near xchg and
cmpxchg; it has been there since 1.3.11 but should not be necessary
with "asm volatile" and a "memory" clobber, neither of which were
there in the original implementation.

However, we *should* make this a volatile reference.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
LKML-Reference: <AANLkTikAmaDPji-TVDarmG1yD=fwbffcsmEU=YEuP+8r@mail.gmail.com>
  • Loading branch information
H. Peter Anvin committed Jul 28, 2010
1 parent 69309a0 commit 4532b30
Show file tree
Hide file tree
Showing 2 changed files with 84 additions and 52 deletions.
75 changes: 42 additions & 33 deletions arch/x86/include/asm/cmpxchg_32.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -11,38 +11,42 @@
extern void __xchg_wrong_size(void);

/*
* Note: no "lock" prefix even on SMP: xchg always implies lock anyway
* Note 2: xchg has side effect, so that attribute volatile is necessary,
* but generally the primitive is invalid, *ptr is output argument. --ANK
* Note: no "lock" prefix even on SMP: xchg always implies lock anyway.
* Since this is generally used to protect other memory information, we
* use "asm volatile" and "memory" clobbers to prevent gcc from moving
* information around.
*/

struct __xchg_dummy {
unsigned long a[100];
};
#define __xg(x) ((struct __xchg_dummy *)(x))

#define __xchg(x, ptr, size) \
({ \
__typeof(*(ptr)) __x = (x); \
switch (size) { \
case 1: \
asm volatile("xchgb %b0,%1" \
: "=q" (__x), "+m" (*__xg(ptr)) \
{ \
volatile u8 *__ptr = (volatile u8 *)(ptr); \
asm volatile("xchgb %0,%1" \
: "=q" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
} \
case 2: \
asm volatile("xchgw %w0,%1" \
: "=r" (__x), "+m" (*__xg(ptr)) \
{ \
volatile u16 *__ptr = (volatile u16 *)(ptr); \
asm volatile("xchgw %0,%1" \
: "=r" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
} \
case 4: \
{ \
volatile u32 *__ptr = (volatile u32 *)(ptr); \
asm volatile("xchgl %0,%1" \
: "=r" (__x), "+m" (*__xg(ptr)) \
: "=r" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
} \
default: \
__xchg_wrong_size(); \
} \
Expand Down Expand Up @@ -94,23 +98,32 @@ extern void __cmpxchg_wrong_size(void);
__typeof__(*(ptr)) __new = (new); \
switch (size) { \
case 1: \
asm volatile(lock "cmpxchgb %b2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
{ \
volatile u8 *__ptr = (volatile u8 *)(ptr); \
asm volatile(lock "cmpxchgb %2,%1" \
: "=a" (__ret), "+m" (*__ptr) \
: "q" (__new), "0" (__old) \
: "memory"); \
break; \
} \
case 2: \
asm volatile(lock "cmpxchgw %w2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
{ \
volatile u16 *__ptr = (volatile u16 *)(ptr); \
asm volatile(lock "cmpxchgw %2,%1" \
: "=a" (__ret), "+m" (*__ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
} \
case 4: \
{ \
volatile u32 *__ptr = (volatile u32 *)(ptr); \
asm volatile(lock "cmpxchgl %2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
: "=a" (__ret), "+m" (*__ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
} \
default: \
__cmpxchg_wrong_size(); \
} \
Expand Down Expand Up @@ -148,31 +161,27 @@ extern void __cmpxchg_wrong_size(void);
(unsigned long long)(n)))
#endif

static inline unsigned long long __cmpxchg64(volatile void *ptr,
unsigned long long old,
unsigned long long new)
static inline u64 __cmpxchg64(volatile u64 *ptr, u64 old, u64 new)
{
unsigned long long prev;
u64 prev;
asm volatile(LOCK_PREFIX "cmpxchg8b %1"
: "=A" (prev),
"+m" (*__xg(ptr))
: "b" ((unsigned long)new),
"c" ((unsigned long)(new >> 32)),
"+m" (*ptr)
: "b" ((u32)new),
"c" ((u32)(new >> 32)),
"0" (old)
: "memory");
return prev;
}

static inline unsigned long long __cmpxchg64_local(volatile void *ptr,
unsigned long long old,
unsigned long long new)
static inline u64 __cmpxchg64_local(volatile u64 *ptr, u64 old, u64 new)
{
unsigned long long prev;
u64 prev;
asm volatile("cmpxchg8b %1"
: "=A" (prev),
"+m" (*__xg(ptr))
: "b" ((unsigned long)new),
"c" ((unsigned long)(new >> 32)),
"+m" (*ptr)
: "b" ((u32)new),
"c" ((u32)(new >> 32)),
"0" (old)
: "memory");
return prev;
Expand Down
61 changes: 42 additions & 19 deletions arch/x86/include/asm/cmpxchg_64.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,6 @@

#include <asm/alternative.h> /* Provides LOCK_PREFIX */

#define __xg(x) ((volatile long *)(x))

static inline void set_64bit(volatile u64 *ptr, u64 val)
{
*ptr = val;
Expand All @@ -14,38 +12,51 @@ extern void __xchg_wrong_size(void);
extern void __cmpxchg_wrong_size(void);

/*
* Note: no "lock" prefix even on SMP: xchg always implies lock anyway
* Note 2: xchg has side effect, so that attribute volatile is necessary,
* but generally the primitive is invalid, *ptr is output argument. --ANK
* Note: no "lock" prefix even on SMP: xchg always implies lock anyway.
* Since this is generally used to protect other memory information, we
* use "asm volatile" and "memory" clobbers to prevent gcc from moving
* information around.
*/
#define __xchg(x, ptr, size) \
({ \
__typeof(*(ptr)) __x = (x); \
switch (size) { \
case 1: \
asm volatile("xchgb %b0,%1" \
: "=q" (__x), "+m" (*__xg(ptr)) \
{ \
volatile u8 *__ptr = (volatile u8 *)(ptr); \
asm volatile("xchgb %0,%1" \
: "=q" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
} \
case 2: \
asm volatile("xchgw %w0,%1" \
: "=r" (__x), "+m" (*__xg(ptr)) \
{ \
volatile u16 *__ptr = (volatile u16 *)(ptr); \
asm volatile("xchgw %0,%1" \
: "=r" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
} \
case 4: \
asm volatile("xchgl %k0,%1" \
: "=r" (__x), "+m" (*__xg(ptr)) \
{ \
volatile u32 *__ptr = (volatile u32 *)(ptr); \
asm volatile("xchgl %0,%1" \
: "=r" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
} \
case 8: \
{ \
volatile u64 *__ptr = (volatile u64 *)(ptr); \
asm volatile("xchgq %0,%1" \
: "=r" (__x), "+m" (*__xg(ptr)) \
: "=r" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
} \
default: \
__xchg_wrong_size(); \
} \
Expand All @@ -69,29 +80,41 @@ extern void __cmpxchg_wrong_size(void);
__typeof__(*(ptr)) __new = (new); \
switch (size) { \
case 1: \
asm volatile(lock "cmpxchgb %b2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
{ \
volatile u8 *__ptr = (volatile u8 *)(ptr); \
asm volatile(lock "cmpxchgb %2,%1" \
: "=a" (__ret), "+m" (*__ptr) \
: "q" (__new), "0" (__old) \
: "memory"); \
break; \
} \
case 2: \
asm volatile(lock "cmpxchgw %w2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
{ \
volatile u16 *__ptr = (volatile u16 *)(ptr); \
asm volatile(lock "cmpxchgw %2,%1" \
: "=a" (__ret), "+m" (*__ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
} \
case 4: \
asm volatile(lock "cmpxchgl %k2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
{ \
volatile u32 *__ptr = (volatile u32 *)(ptr); \
asm volatile(lock "cmpxchgl %2,%1" \
: "=a" (__ret), "+m" (*__ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
} \
case 8: \
{ \
volatile u64 *__ptr = (volatile u64 *)(ptr); \
asm volatile(lock "cmpxchgq %2,%1" \
: "=a" (__ret), "+m" (*__xg(ptr)) \
: "=a" (__ret), "+m" (*__ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
} \
default: \
__cmpxchg_wrong_size(); \
} \
Expand Down

0 comments on commit 4532b30

Please sign in to comment.