Re: [PATCH 4/5] x86/asm/entry/32: Replace RESTORE_RSI_RDI[_RDX] with open-coded 32-bit reads

Denys Vlasenko
2015-06-09T19:04:08Z

On 06/09/2015 09:01 PM, Andy Lutomirski wrote:
> On Tue, Jun 9, 2015 at 11:54 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
>> This doesn't change much, but this uses shorter 32-bit insns:
>>
>> -48 8b 74 24 68 mov 0x68(%rsp),%rsi
>> -48 8b 7c 24 70 mov 0x70(%rsp),%rdi
>> -48 8b 54 24 60 mov 0x60(%rsp),%rdx
>> +8b 74 24 68 mov 0x68(%rsp),%esi
>> +8b 7c 24 70 mov 0x70(%rsp),%edi
>> +8b 54 24 60 mov 0x60(%rsp),%edx
>>
>> Since these are the only uses of RESTORE_RSI_RDI[_RDX], drop these macros.
>>
>
> It probably doesn't matter for these fast paths, but, for the full
> slow path return, we really do need to restore the full pt_regs.
> After all, the syscall we're returning from might be sigreturn.

This is compat 32-bit syscall handling code.
IIUC we do not restore high half of any registers for 32-bit tasks.

Am I missing something?