Re: RFC: [PATCH] x86: Add -mzero-caller-saved-regs=[skip|used|all]

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Thu, Sep 27, 2018 at 12:24 PM, Florian Weimer <fweimer@redhat.com> wrote:
> * H. J. Lu:
>
>> +@item zero_caller_saved_regs("@var{choice}")
>> +@cindex @code{zero_caller_saved_regs} function attribute, x86
>> +On x86 targets, the @code{zero_caller_saved_regs} attribute causes the
>> +compiler to zero caller-saved integer registers at function return with
>> +@var{choice}.  @samp{skip} doesn't zero caller-saved integer registers.
>> +@samp{used} zeros caller-saved integer registers which are used in
>> +function.  @samp{all} zeros all caller-saved integer registers.
>
> Perhaps “according to @var{choice}:”.  And say that the default for the
> attribute is controlled by @option{-mzero-caller-saved-regs}?

Sure.

> (Maybe “skip” should be none?)

I have no strong opinion here.

> I assume we can check for this use __has_attribute?  We would use this

Yes.

> in the implementation of explicit_bzero in glibc.

Good to know.

>> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
>> index 7ef4e7a449b..796477452d5 100644
>> --- a/gcc/doc/invoke.texi
>> +++ b/gcc/doc/invoke.texi
>
>> @@ -28459,6 +28459,16 @@ not be reachable in the large code model.
>>  @opindex -mindirect-branch-register
>>  Force indirect call and jump via register.
>
>> +@item -mzero-caller-saved-regs=@var{choice}
>> +@opindex -mzero-caller-saved-regs
>> +Zero caller-saved integer registers at function return with @var{choice}.
>> +The default is @samp{skip}, which doesn't zero caller-saved integer
>> +registers.  @samp{used} zeros caller-saved integer registers which are
>> +used in function.  @samp{all} zeros all caller-saved integer registers.
>> +You can control this behavior for a specific function by using the
>> +function attribute @code{zero_caller_saved_regs}.
>> +@xref{Function Attributes}.
>
> See above regarding “with @var{choice}”.

I will update it.

Thanks.


-- 
H.J.