Re: [2.4] gcc3 warns about type-punned pointers ?
From: insecure
Date: Fri Aug 29 2003 - 21:46:53 EST
> A collateral question: why is the reason for this function ?
> long long assignments are not atomic in gcc ?
Another question: why do we do _double_ store here?
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 cmpxchg8b (%0)\n\t"
"jnz 1b"
: /* no outputs */
: "D"(ptr),
"b"(low),
"c"(high)
: "ax","dx","memory");
}
This will execute expensive locked load-compare-store operation twice
almost always (unless previous value was already equal
to the value we are about to store)
AFAIK we can safely drop that loop (jnz instruction)
--
vda
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