Re: [PATCH] WorkStruct: Implement generic UP cmpxchg() where an arch doesn't support it

David Howells
2006-12-11T11:04:41Z

Russell King <rmk+lkml@arm.linux.org.uk> wrote:

> Yes you can. Well, you can on ARM at least. Between the load exclusive
> you can do anything you like until you hit the store exclusive.

How come atomic_set() on arm6 is implemented as:

static inline void atomic_set(atomic_t *v, int i)
{
unsigned long tmp;

__asm__ __volatile__("@ atomic_set\n"
"1: ldrex %0, [%1]\n"
" strex %0, %2, [%1]\n"
" teq %0, #0\n"
" bne 1b"
: "=&r" (tmp)
: "r" (&v->counter), "r" (i)
: "cc");
}

Why LDREX/STREX and not direct assignment?

David