Re: [PATCH kvm-unit-test 2/6] Introduce atomic operations

Avi Kivity
2010-08-29T09:39:48Z

On 08/27/2010 02:39 PM, Glauber Costa wrote:
> On Fri, Aug 27, 2010 at 01:49:20PM +0800, Jason Wang wrote:
>> +u64 atomic64_cmpxchg(atomic64_t *v, u64 old, u64 new)
>> +{
>> + u64 ret;
>> + u64 _old = old;
>> + u64 _new = new;
>> +
>> + asm volatile("lock cmpxchgq %1,%2"
>> + : "=a" (ret)
>> + : "r" (_new),
>> + "m" (*(volatile long *)&v->counter), "0"(_old)
>> + : "memory"
>> + );
>> + return ret;
>> +}
>> +
> This is wrong.
> See http://git.kernel.org/?p=linux/kernel/git/x86/linux-2.6-tip.git;a=commitdiff;h=113fc5a6e8c2288619ff7e8187a6f556b7e0d372
>
> you need to explicitly mark you are changing the memory, here.
>
> Btw, this is mostly header copying, and can miss bug fixes like the one above. Isn't there
> a way to just specify in the test they are needed, and then grab them from linux automatically?

That may pull in dependencies. I'd prefer using builtins like
__sync_val_compare_and_swap() (but many atomics are not available). Is
there some library we can use for this?

--
error compiling committee.c: too many arguments to function