On Tue, Dec 6, 2016 at 1:49 AM, Jan Beulich <[email protected]> wrote:
>>>> On 06.12.16 at 10:25, <[email protected]> wrote:
>> On Tue, Dec 06, 2016 at 01:46:37AM -0700, Jan Beulich wrote:
>>> > + asm volatile (
>>> > + "pushfl\n\t"
>>> > + "pushl %%cs\n\t"
>>> > + "pushl $1f\n\t"
>>> > + "iret\n\t"
>>> > + "1:"
>>> > + : "+r" (__sp) : : "cc", "memory");
>>>
>>> I don't thing EFLAGS (i.e. "cc") gets modified anywhere here. And
>>> the memory clobber would perhaps better be pulled out into an
>>> explicit barrier() invocation (making it more obvious what it's needed
>>> for)?
>>
>> EVerything that implies a memory barrier (and I think serializing
>> instructions do that) also imply a compiler barrier.
>>
>> Not doing the memory clobber gets you inconsistency wrt everything else.
>
> Well, I didn't say dropping the memory clobber altogether, but
> split it into a separate barrier() invocation (placed perhaps after
> the #endif).
I'll add a comment. I'm fixing up the constraints, too. (Although if
gcc allocated tmp into rsp, that would be very strange indeed.)
--Andy