>>> On 04.06.13 at 23:53, Mukesh Rathor <mukesh.rat...@oracle.com> wrote:
> Following OK? :
>
> if (xen_feature(XENFEAT_auto_translated_physmap)) {
> switch_to_new_gdt(0);
>
> asm volatile (
> "pushq %%rax\n"
> "leaq 1f(%%rip),%%rax\n"
> "pushq %%rax\n"
> "lretq\n"
> "1:\n"
> : : "a" (__KERNEL_CS) : "memory");
>
> return;
> }
While generally the choice of using %%rax instead of %0 here is
a matter of taste to some degree, I still don't see why you can't
use "r" as the constraint here in the first place.
Furthermore, assuming this sits in a function guaranteed to not be
inlined, this has a latent bug (and if the assumption isn't right, the
bug is real) in that the asm() modifies %rax without telling the
compiler.
This is how I would have done it:
unsigned long dummy;
asm volatile ("pushq %0\n"
"leaq 1f(%%rip),%0\n"
"pushq %0\n"
"lretq\n"
"1:\n"
: "=&r" (dummy) : "0" (__KERNEL_CS));
(also dropping the memory clobber, as I don't see what you
need this for).
Jan
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