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

[Denys Vlasenko]

On 06/09/2015 09:01 PM, Andy Lutomirski wrote:
> On Tue, Jun 9, 2015 at 11:54 AM, Denys Vlasenko <dvlasenk@xxxxxxxxxx> 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?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/