On 05/23/2018 11:41 AM, Jan Beulich wrote: >>>> 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.
Sure, I can replace these two with 32-bit variants. If there are no other comments I won't re-send this again. -boris
