On Thu, Jan 31, 2002 at 11:17:21PM +0100, Maciej W. Rozycki wrote:
> On Thu, 31 Jan 2002, H . J . Lu wrote:
>
> > (__compare_and_swap): Return 0 when failed to compare or swap.
> [...]
> > * sysdeps/mips/atomicity.h (compare_and_swap): Return 0 when
> > failed to compare or swap.
>
> Looking at the i486 implementation these are not expected to fail.
> Unless I am missing something...
Why can't it fail?
static inline char
__attribute__ ((unused))
compare_and_swap (volatile long int *p, long int oldval, long int newval)
{
char ret;
long int readval;
__asm__ __volatile__ ("lock; cmpxchgl %3, %1; sete %0"
: "=q" (ret), "=m" (*p), "=a" (readval)
: "r" (newval), "1" (*p), "a" (oldval));
return ret;
}
It will fail if *p is not same as oldval.
>
> > * sysdeps/unix/sysv/linux/mips/sys/tas.h (_test_and_set): Fill
> > the delay slot.
>
> What's the difference? The code looks the same after changes. Also you
> forgot to indent instructions in delay slots, which worsens readability.
Are we looking at the same file? Here is the patched version:
_EXTERN_INLINE int
_test_and_set (int *p, int v) __THROW
{
int r, t;
__asm__ __volatile__
(".set push\n\t"
".set noreorder\n"
"1:\n\t"
"ll %0,%3\n\t"
"beq %0,%4,2f\n\t"
"move %1,%4\n\t"
"sc %1,%2\n\t"
"beqz %1,1b\n\t"
"nop\n"
"2:\n\t"
".set pop"
: "=&r" (r), "=&r" (t), "=m" (*p)
: "m" (*p), "r" (v)
: "memory");
return r;
}
H.J.
