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powerpc: Fix casueword(9) post-r349951

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'=' asm constraint marks a variable as write-only.  Because of this, gcc
throws away the initialization of 'res', causing garbage to be returned if
the CAS was successful.  Use '+' to mark res as read/write, so that the
initialization stays in the generated asm.  Also, fix the reservation
clearing stwcx store index register in casueword32, and only do the dummy
store when needed, skip it if the real store has already succeeded.
This commit is contained in:
jhibbits 2019-07-16 03:55:27 +00:00
parent 59c3949700
commit 462a300755
1 changed files with 11 additions and 11 deletions
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22
sys/powerpc/powerpc/copyinout.c
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@ -456,13 +456,13 @@ casueword32(volatile uint32_t *addr, uint32_t old, uint32_t *oldvalp,
"cmplw %4, %0\n\t" /* compare */
"bne 1f\n\t" /* exit if not equal */
"stwcx. %5, 0, %3\n\t" /* attempt to store */
"bne- 1f\n\t" /* if failed */
"b 2f\n\t" /* we've succeeded */
"bne- 2f\n\t" /* if failed */
"b 3f\n\t" /* we've succeeded */
"1:\n\t"
"stwcx. %0, 0, %4\n\t" /* clear reservation (74xx) */
"li %2, 1\n\t"
"2:\n\t"
: "=&r" (val), "=m" (*p), "=&r" (res)
"stwcx. %0, 0, %3\n\t" /* clear reservation (74xx) */
"2:li %2, 1\n\t"
"3:\n\t"
: "=&r" (val), "=m" (*p), "+&r" (res)
: "r" (p), "r" (old), "r" (new), "m" (*p)
: "cr0", "memory");
@ -511,13 +511,13 @@ casueword(volatile u_long *addr, u_long old, u_long *oldvalp, u_long new)
"cmpld %4, %0\n\t" /* compare */
"bne 1f\n\t" /* exit if not equal */
"stdcx. %5, 0, %3\n\t" /* attempt to store */
"bne- 1f\n\t" /* if failed */
"b 2f\n\t" /* we've succeeded */
"bne- 2f\n\t" /* if failed */
"b 3f\n\t" /* we've succeeded */
"1:\n\t"
"stdcx. %0, 0, %3\n\t" /* clear reservation (74xx) */
"li %2, 1\n\t"
"2:\n\t"
: "=&r" (val), "=m" (*p), "=&r" (res)
"2:li %2, 1\n\t"
"3:\n\t"
: "=&r" (val), "=m" (*p), "+&r" (res)
: "r" (p), "r" (old), "r" (new), "m" (*p)
: "cr0", "memory");