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Commit1098677

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Adjust TAS assembly as per recent discussions: use "+m"(*lock) everywhere
to reference the spinlock variable, and specify "memory" as a clobberoperand to be sure gcc does not try to keep shared-memory values inregisters across a spinlock acquisition. Also tighten the S/390 asmsequence, which was apparently written with only minimal study of thegcc 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.
1 parentc1d9dec commit1098677

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1 file changed

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-101
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1 file changed

+79
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‎src/include/storage/s_lock.h‎

Lines changed: 79 additions & 101 deletions
Original file line numberDiff line numberDiff line change
@@ -66,7 +66,7 @@
6666
* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
6767
* Portions Copyright (c) 1994, Regents of the University of California
6868
*
69-
* $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.125 2004/01/03 05:47:44 tgl Exp $
69+
* $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.126 2004/06/19 23:02:32 tgl Exp $
7070
*
7171
*-------------------------------------------------------------------------
7272
*/
@@ -85,16 +85,26 @@
8585
* Other compilers use __cpu or __cpu__ so we test for both in those cases.
8686
*/
8787

88-
/*
89-
* Standard gcc asm formatis:
90-
*
88+
/*----------
89+
* Standard gcc asm format(assuming "volatile slock_t *lock"):
90+
9191
__asm__ __volatile__(
92-
"command\n"
93-
"command\n"
94-
"command\n"
95-
:"=r"(_res)return value, in register
96-
:"r"(lock)argument, 'lock pointer', in register
97-
:"r0");inline code uses this register
92+
"instruction\n"
93+
"instruction\n"
94+
"instruction\n"
95+
:"=r"(_res), "+m"(*lock)// return register, in/out lock value
96+
:"r"(lock)// lock pointer, in input register
97+
:"memory", "cc");// show clobbered registers here
98+
99+
* The output-operands list (after first colon) should always include
100+
* "+m"(*lock), whether or not the asm code actually refers to this
101+
* operand directly. This ensures that gcc believes the value in the
102+
* lock variable is used and set by the asm code. Also, the clobbers
103+
* list (after third colon) should always include "memory"; this prevents
104+
* gcc from thinking it can cache the values of shared-memory fields
105+
* across the asm code. Add "cc" if your asm code changes the condition
106+
* code register, and also list any temp registers the code uses.
107+
*----------
98108
*/
99109

100110

@@ -117,8 +127,9 @@ tas(volatile slock_t *lock)
117127
"lock\n"
118128
"xchgb%0,%1\n"
119129
"1: \n"
120-
:"=q"(_res),"=m"(*lock)
121-
:"0"(_res));
130+
:"+q"(_res),"+m"(*lock)
131+
:
132+
:"memory","cc");
122133
return (int)_res;
123134
}
124135

@@ -128,8 +139,7 @@ static __inline__ void
128139
spin_delay(void)
129140
{
130141
__asm__ __volatile__(
131-
" rep; nop\n"
132-
: : :"memory");
142+
" rep; nop\n");
133143
}
134144

135145
#endif/* __i386__ || __x86_64__ */
@@ -150,10 +160,9 @@ tas(volatile slock_t *lock)
150160

151161
__asm__ __volatile__(
152162
"xchg4 %0=%1,%2\n"
153-
:"=r"(ret),"=m"(*lock)
154-
:"r"(1),"1"(*lock)
163+
:"=r"(ret),"+m"(*lock)
164+
:"r"(1)
155165
:"memory");
156-
157166
return (int)ret;
158167
}
159168

@@ -173,46 +182,18 @@ tas(volatile slock_t *lock)
173182
registerslock_t_res=1;
174183

175184
__asm__ __volatile__(
176-
"swpb %0, %0, [%3]\n"
177-
:"=r"(_res),"=m"(*lock)
178-
:"0"(_res),"r"(lock));
185+
"swpb %0, %0, [%2]\n"
186+
:"+r"(_res),"+m"(*lock)
187+
:"r"(lock)
188+
:"memory");
179189
return (int)_res;
180190
}
181191

182192
#endif/* __arm__ */
183193

184194

185-
#if defined(__s390__)&& !defined(__s390x__)
186-
/* S/390 Linux */
187-
#defineHAS_TEST_AND_SET
188-
189-
typedefunsignedintslock_t;
190-
191-
#defineTAS(lock) tas(lock)
192-
193-
static __inline__int
194-
tas(volatileslock_t*lock)
195-
{
196-
int_res;
197-
198-
__asm____volatile__(
199-
"la1,1\n"
200-
"l 2,%2\n"
201-
"slr 0,0\n"
202-
"cs 0,1,0(2)\n"
203-
"lr %1,0\n"
204-
:"=m"(lock),"=d"(_res)
205-
:"m"(lock)
206-
:"0","1","2");
207-
208-
return (_res);
209-
}
210-
211-
#endif/* __s390__ */
212-
213-
214-
#if defined(__s390x__)
215-
/* S/390x Linux (64-bit zSeries) */
195+
#if defined(__s390__)|| defined(__s390x__)
196+
/* S/390 and S/390x Linux (32- and 64-bit zSeries) */
216197
#defineHAS_TEST_AND_SET
217198

218199
typedefunsignedintslock_t;
@@ -222,22 +203,17 @@ typedef unsigned int slock_t;
222203
static __inline__int
223204
tas(volatileslock_t*lock)
224205
{
225-
int_res;
206+
int_res=0;
226207

227208
__asm____volatile__(
228-
"la1,1\n"
229-
"lg 2,%2\n"
230-
"slr 0,0\n"
231-
"cs 0,1,0(2)\n"
232-
"lr %1,0\n"
233-
:"=m"(lock),"=d"(_res)
234-
:"m"(lock)
235-
:"0","1","2");
236-
237-
return (_res);
209+
"cs %0,%3,0(%2)\n"
210+
:"+d"(_res),"+m"(*lock)
211+
:"a"(lock),"d"(1)
212+
:"memory","cc");
213+
return_res;
238214
}
239215

240-
#endif/* __s390x__ */
216+
#endif/*__s390__ ||__s390x__ */
241217

242218

243219
#if defined(__sparc__)
@@ -250,12 +226,13 @@ typedef unsigned char slock_t;
250226
static __inline__int
251227
tas(volatileslock_t*lock)
252228
{
253-
registerslock_t_res=1;
229+
registerslock_t_res;
254230

255231
__asm__ __volatile__(
256232
"ldstub[%2], %0\n"
257-
:"=r"(_res),"=m"(*lock)
258-
:"r"(lock));
233+
:"=r"(_res),"+m"(*lock)
234+
:"r"(lock)
235+
:"memory");
259236
return (int)_res;
260237
}
261238

@@ -283,11 +260,11 @@ tas(volatile slock_t *lock)
283260
int_res;
284261

285262
__asm__ __volatile__(
286-
"lwarx %0,0,%2\n"
263+
"lwarx %0,0,%3\n"
287264
"cmpwi %0,0\n"
288265
"bne 1f\n"
289266
"addi %0,%0,1\n"
290-
"stwcx. %0,0,%2\n"
267+
"stwcx. %0,0,%3\n"
291268
"beq 2f \n"
292269
"1:li %1,1\n"
293270
"b3f\n"
@@ -296,10 +273,9 @@ tas(volatile slock_t *lock)
296273
"li %1,0\n"
297274
"3:\n"
298275

299-
:"=&r" (_t),"=r" (_res)
300-
:"r" (lock)
301-
:"cc","memory"
302-
);
276+
:"=&r"(_t),"=r"(_res),"+m"(*lock)
277+
:"r"(lock)
278+
:"memory","cc");
303279
return_res;
304280
}
305281

@@ -330,10 +306,9 @@ tas(volatile slock_t *lock)
330306
"clrl%0\n"
331307
"tas%1\n"
332308
"sne%0\n"
333-
:"=d"(rv),"=m"(*lock)
334-
:"1"(*lock)
335-
:"cc");
336-
309+
:"=d"(rv),"+m"(*lock)
310+
:
311+
:"memory","cc");
337312
returnrv;
338313
}
339314

@@ -357,13 +332,13 @@ tas(volatile slock_t *lock)
357332
registerint_res;
358333

359334
__asm__ __volatile__(
360-
"movl $1,r0\n"
361-
"bbssi$0, (%1), 1f\n"
362-
"clrlr0\n"
363-
"1:movlr0, %0\n"
364-
:"=r"(_res)
335+
"movl $1,%0\n"
336+
"bbssi$0, (%2), 1f\n"
337+
"clrl%0\n"
338+
"1:\n"
339+
:"=&r"(_res),"+m"(*lock)
365340
:"r"(lock)
366-
:"r0");
341+
:"memory");
367342
return_res;
368343
}
369344

@@ -383,9 +358,11 @@ tas(volatile slock_t *lock)
383358
registerint_res;
384359

385360
__asm__ __volatile__(
386-
"sbitb0, %0\n"
387-
"sfsd%1\n"
388-
:"=m"(*lock),"=r"(_res));
361+
"sbitb0, %1\n"
362+
"sfsd%0\n"
363+
:"=r"(_res),"+m"(*lock)
364+
:
365+
:"memory");
389366
return_res;
390367
}
391368

@@ -404,37 +381,37 @@ tas(volatile slock_t *lock)
404381
typedefunsigned longslock_t;
405382

406383
#defineTAS(lock) tas(lock)
407-
#defineS_UNLOCK(lock)\
408-
do \
409-
{\
410-
__asm__ __volatile__ ("mb \n"); \
411-
*((volatile slock_t *) (lock)) = 0; \
412-
} while (0)
413384

414385
static __inline__int
415386
tas(volatileslock_t*lock)
416387
{
417388
registerslock_t_res;
418389

419390
__asm____volatile__(
420-
"ldq$0, %0\n"
391+
"ldq$0, %1\n"
421392
"bne$0, 2f\n"
422-
"ldq_l%1, %0\n"
423-
"bne%1, 2f\n"
393+
"ldq_l%0, %1\n"
394+
"bne%0, 2f\n"
424395
"mov1, $0\n"
425-
"stq_c$0, %0\n"
396+
"stq_c$0, %1\n"
426397
"beq$0, 2f\n"
427398
"mb\n"
428399
"br3f\n"
429-
"2:mov1, %1\n"
400+
"2:mov1, %0\n"
430401
"3:\n"
431-
:"=m"(*lock),"=r"(_res)
402+
:"=&r"(_res),"+m"(*lock)
432403
:
433-
:"0");
434-
404+
:"memory","0");
435405
return (int)_res;
436406
}
437407

408+
#defineS_UNLOCK(lock)\
409+
do \
410+
{\
411+
__asm__ __volatile__ ("mb \n"); \
412+
*((volatile slock_t *) (lock)) = 0; \
413+
} while (0)
414+
438415
#endif/* __alpha || __alpha__ */
439416

440417

@@ -540,8 +517,9 @@ tas(volatile slock_t *lock)
540517

541518
__asm__ __volatile__(
542519
"ldcwx0(0,%2),%0\n"
543-
:"=r"(lockval),"=m"(*lockword)
544-
:"r"(lockword));
520+
:"=r"(lockval),"+m"(*lockword)
521+
:"r"(lockword)
522+
:"memory");
545523
return (lockval==0);
546524
}
547525

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