From 109867748259d286dd01fce17d5f895ce59c68d5 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 19 Jun 2004 23:02:32 +0000
Subject: [PATCH] Adjust TAS assembly as per recent discussions: use
"+m"(*lock) everywhere to reference the spinlock variable, and specify
"memory" as a clobber operand to be sure gcc does not try to keep
shared-memory values in registers across a spinlock acquisition. Also
tighten the S/390 asm sequence, which was apparently written with only
minimal study of the gcc asm documentation. I have personally tested i386,
ia64, ppc, hppa, and s390 variants --- there is some small chance that I
broke the others, but I doubt it.
---
src/include/storage/s_lock.h | 180 +++++++++++++++--------------------
1 file changed, 79 insertions(+), 101 deletions(-)
diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h
index f8bcf5e96a9..0725fd06d24 100644
--- a/src/include/storage/s_lock.h
+++ b/src/include/storage/s_lock.h
@@ -66,7 +66,7 @@
* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.125 2004/01/03 05:47:44 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.126 2004/06/19 23:02:32 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -85,16 +85,26 @@
* Other compilers use __cpu or __cpu__ so we test for both in those cases.
*/
-/*
- * Standard gcc asm format is:
- *
+/*----------
+ * Standard gcc asm format (assuming "volatile slock_t *lock"):
+
__asm__ __volatile__(
- " command \n"
- " command \n"
- " command \n"
-: "=r"(_res) return value, in register
-: "r"(lock) argument, 'lock pointer', in register
-: "r0"); inline code uses this register
+ " instruction \n"
+ " instruction \n"
+ " instruction \n"
+: "=r"(_res), "+m"(*lock) // return register, in/out lock value
+: "r"(lock) // lock pointer, in input register
+: "memory", "cc"); // show clobbered registers here
+
+ * The output-operands list (after first colon) should always include
+ * "+m"(*lock), whether or not the asm code actually refers to this
+ * operand directly. This ensures that gcc believes the value in the
+ * lock variable is used and set by the asm code. Also, the clobbers
+ * list (after third colon) should always include "memory"; this prevents
+ * gcc from thinking it can cache the values of shared-memory fields
+ * across the asm code. Add "cc" if your asm code changes the condition
+ * code register, and also list any temp registers the code uses.
+ *----------
*/
@@ -117,8 +127,9 @@ tas(volatile slock_t *lock)
" lock \n"
" xchgb %0,%1 \n"
"1: \n"
-: "=q"(_res), "=m"(*lock)
-: "0"(_res));
+: "+q"(_res), "+m"(*lock)
+:
+: "memory", "cc");
return (int) _res;
}
@@ -128,8 +139,7 @@ static __inline__ void
spin_delay(void)
{
__asm__ __volatile__(
- " rep; nop \n"
- : : : "memory");
+ " rep; nop \n");
}
#endif /* __i386__ || __x86_64__ */
@@ -150,10 +160,9 @@ tas(volatile slock_t *lock)
__asm__ __volatile__(
" xchg4 %0=%1,%2 \n"
-: "=r"(ret), "=m"(*lock)
-: "r"(1), "1"(*lock)
+: "=r"(ret), "+m"(*lock)
+: "r"(1)
: "memory");
-
return (int) ret;
}
@@ -173,46 +182,18 @@ tas(volatile slock_t *lock)
register slock_t _res = 1;
__asm__ __volatile__(
- " swpb %0, %0, [%3] \n"
-: "=r"(_res), "=m"(*lock)
-: "0"(_res), "r"(lock));
+ " swpb %0, %0, [%2] \n"
+: "+r"(_res), "+m"(*lock)
+: "r"(lock)
+: "memory");
return (int) _res;
}
#endif /* __arm__ */
-#if defined(__s390__) && !defined(__s390x__)
-/* S/390 Linux */
-#define HAS_TEST_AND_SET
-
-typedef unsigned int slock_t;
-
-#define TAS(lock) tas(lock)
-
-static __inline__ int
-tas(volatile slock_t *lock)
-{
- int _res;
-
- __asm__ __volatile__(
- " la 1,1 \n"
- " l 2,%2 \n"
- " slr 0,0 \n"
- " cs 0,1,0(2) \n"
- " lr %1,0 \n"
-: "=m"(lock), "=d"(_res)
-: "m"(lock)
-: "0", "1", "2");
-
- return (_res);
-}
-
-#endif /* __s390__ */
-
-
-#if defined(__s390x__)
-/* S/390x Linux (64-bit zSeries) */
+#if defined(__s390__) || defined(__s390x__)
+/* S/390 and S/390x Linux (32- and 64-bit zSeries) */
#define HAS_TEST_AND_SET
typedef unsigned int slock_t;
@@ -222,22 +203,17 @@ typedef unsigned int slock_t;
static __inline__ int
tas(volatile slock_t *lock)
{
- int _res;
+ int _res = 0;
__asm__ __volatile__(
- " la 1,1 \n"
- " lg 2,%2 \n"
- " slr 0,0 \n"
- " cs 0,1,0(2) \n"
- " lr %1,0 \n"
-: "=m"(lock), "=d"(_res)
-: "m"(lock)
-: "0", "1", "2");
-
- return (_res);
+ " cs %0,%3,0(%2) \n"
+: "+d"(_res), "+m"(*lock)
+: "a"(lock), "d"(1)
+: "memory", "cc");
+ return _res;
}
-#endif /* __s390x__ */
+#endif /* __s390__ || __s390x__ */
#if defined(__sparc__)
@@ -250,12 +226,13 @@ typedef unsigned char slock_t;
static __inline__ int
tas(volatile slock_t *lock)
{
- register slock_t _res = 1;
+ register slock_t _res;
__asm__ __volatile__(
" ldstub [%2], %0 \n"
-: "=r"(_res), "=m"(*lock)
-: "r"(lock));
+: "=r"(_res), "+m"(*lock)
+: "r"(lock)
+: "memory");
return (int) _res;
}
@@ -283,11 +260,11 @@ tas(volatile slock_t *lock)
int _res;
__asm__ __volatile__(
-" lwarx %0,0,%2 \n"
+" lwarx %0,0,%3 \n"
" cmpwi %0,0 \n"
" bne 1f \n"
" addi %0,%0,1 \n"
-" stwcx. %0,0,%2 \n"
+" stwcx. %0,0,%3 \n"
" beq 2f \n"
"1: li %1,1 \n"
" b 3f \n"
@@ -296,10 +273,9 @@ tas(volatile slock_t *lock)
" li %1,0 \n"
"3: \n"
-: "=&r" (_t), "=r" (_res)
-: "r" (lock)
-: "cc", "memory"
- );
+: "=&r"(_t), "=r"(_res), "+m"(*lock)
+: "r"(lock)
+: "memory", "cc");
return _res;
}
@@ -330,10 +306,9 @@ tas(volatile slock_t *lock)
" clrl %0 \n"
" tas %1 \n"
" sne %0 \n"
-: "=d"(rv), "=m"(*lock)
-: "1"(*lock)
-: "cc");
-
+: "=d"(rv), "+m"(*lock)
+:
+: "memory", "cc");
return rv;
}
@@ -357,13 +332,13 @@ tas(volatile slock_t *lock)
register int _res;
__asm__ __volatile__(
- " movl $1, r0 \n"
- " bbssi $0, (%1), 1f \n"
- " clrl r0 \n"
- "1: movl r0, %0 \n"
-: "=r"(_res)
+ " movl $1, %0 \n"
+ " bbssi $0, (%2), 1f \n"
+ " clrl %0 \n"
+ "1: \n"
+: "=&r"(_res), "+m"(*lock)
: "r"(lock)
-: "r0");
+: "memory");
return _res;
}
@@ -383,9 +358,11 @@ tas(volatile slock_t *lock)
register int _res;
__asm__ __volatile__(
- " sbitb 0, %0 \n"
- " sfsd %1 \n"
-: "=m"(*lock), "=r"(_res));
+ " sbitb 0, %1 \n"
+ " sfsd %0 \n"
+: "=r"(_res), "+m"(*lock)
+:
+: "memory");
return _res;
}
@@ -404,12 +381,6 @@ tas(volatile slock_t *lock)
typedef unsigned long slock_t;
#define TAS(lock) tas(lock)
-#define S_UNLOCK(lock) \
-do \
-{\
- __asm__ __volatile__ (" mb \n"); \
- *((volatile slock_t *) (lock)) = 0; \
-} while (0)
static __inline__ int
tas(volatile slock_t *lock)
@@ -417,24 +388,30 @@ tas(volatile slock_t *lock)
register slock_t _res;
__asm__ __volatile__(
- " ldq $0, %0 \n"
+ " ldq $0, %1 \n"
" bne $0, 2f \n"
- " ldq_l %1, %0 \n"
- " bne %1, 2f \n"
+ " ldq_l %0, %1 \n"
+ " bne %0, 2f \n"
" mov 1, $0 \n"
- " stq_c $0, %0 \n"
+ " stq_c $0, %1 \n"
" beq $0, 2f \n"
" mb \n"
" br 3f \n"
- "2: mov 1, %1 \n"
+ "2: mov 1, %0 \n"
"3: \n"
-: "=m"(*lock), "=r"(_res)
+: "=&r"(_res), "+m"(*lock)
:
-: "0");
-
+: "memory", "0");
return (int) _res;
}
+#define S_UNLOCK(lock) \
+do \
+{\
+ __asm__ __volatile__ (" mb \n"); \
+ *((volatile slock_t *) (lock)) = 0; \
+} while (0)
+
#endif /* __alpha || __alpha__ */
@@ -540,8 +517,9 @@ tas(volatile slock_t *lock)
__asm__ __volatile__(
" ldcwx 0(0,%2),%0 \n"
-: "=r"(lockval), "=m"(*lockword)
-: "r"(lockword));
+: "=r"(lockval), "+m"(*lockword)
+: "r"(lockword)
+: "memory");
return (lockval == 0);
}
--
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