>>> On 23.05.18 at 16:30, <boris.ostrov...@oracle.com> wrote: > @@ -98,6 +101,12 @@ ENTRY(pvh_start_xen) > /* 64-bit entry point. */ > .code64 > 1: > + /* Set base address in stack canary descriptor. */ > + mov $MSR_GS_BASE,%ecx > + mov $_pa(canary), %rax > + xor %rdx, %rdx
Why rax and rdx instead of eax and edx? In the former case, the relocation produced might confuse whatever entity processing it (it'll have a sign-extended 32-bit quantity to deal with, which wouldn't allow representing an address in the [2Gb, 4Gb) range). In the latter case, while surely neither performance nor code size matter much here, it's still a bad precedent (people copy-and-paste code all the time): Zero-ing of registers should generally use the 32-bit forms of the insn. Gas has actually gained an optimization mode recently (upon request from Linus and the x86 maintainers) to silently "repair" such inefficiencies. Jan
