On 12/26/2009 09:56 PM, Dan Kruchinin wrote:
> I'm not sure if I found out a bug or I just made a mistake in gcc inline assembler.
> I think that more probably it's a bug, because my code works well when I don't use compile time optimization.
> I have the following code for x86_64 target:
> ===
> #include <stdio.h>
>
> #define SPIN_LOCKED_V 1
> #define SPIN_UNLOCKED_V 0
>
> struct spin {
> unsigned long val;
> };
>
> static inline void spin_lock(struct spin *lock)
> {
> __asm__ volatile ("movq %2, %%rax\n\t"
> "1: lock cmpxchg %1, %0\n\t"
> "cmpq %2, %%rax\n\t"
> "jnz 1b\n"
> : "+m" (lock->val)
> : "r" ((volatile long)SPIN_LOCKED_V),
> "rI" ((volatile long)SPIN_UNLOCKED_V)
> : "%rax", "memory");
> }
> static inline void spin_unlock(struct spin *lock)
> {
> __asm__ volatile ("lock xchgq %1, %0\n"
> : "+m" (lock->val)
> : "r" ((volatile long)SPIN_UNLOCKED_V));
> }
You need a memory clobber here.
You need to add a clobber to Operand 1.
Andrew.
