[PATCH] i386: Replace PREINIT_FUNCTION@PLT with *%eax in call

[H.J. Lu]

On Mon, May 14, 2018 at 8:46 AM, Christian Brauner <christian@brauner.io> wrote:
> On Sat, May 12, 2018 at 06:31:45AM -0700, H.J. Lu wrote:
>> Since we have loaded address of PREINIT_FUNCTION into %eax, we can
>> avoid extra branch to PLT slot.
>>
>> Any comments?
>>
>> H.J.
>> ---
>>       * sysdeps/i386/crti.S (_init): Replace PREINIT_FUNCTION@PLT
>>       with *%eax in call.
>> ---
>>  sysdeps/i386/crti.S | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/sysdeps/i386/crti.S b/sysdeps/i386/crti.S
>> index c0422f9ce3..065460b813 100644
>> --- a/sysdeps/i386/crti.S
>> +++ b/sysdeps/i386/crti.S
>> @@ -68,7 +68,7 @@ _init:
>>       movl PREINIT_FUNCTION@GOT(%ebx), %eax
>>       testl %eax, %eax
>>       je .Lno_weak_fn
>> -     call PREINIT_FUNCTION@PLT
>
> The PREINIT_FUNCTION macro is essentially just __gmon_start__, right? So

That is correct.

> unless this was somehow introduced specifically for profiling purposes
> this seems legit.

x86-64 already has some similar:

movq PREINIT_FUNCTION@GOTPCREL(%rip), %rax
testq %rax, %rax
je .Lno_weak_fn
call *%rax
.Lno_weak_fn:

> Acked-by: Christian Brauner (Ubuntu) <christian@brauner.io>

I am going to check it in.

-- 
H.J.