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Re: [PATCH] i386: Replace PREINIT_FUNCTION@PLT with *%eax in call
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Christian Brauner <christian at brauner dot io>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Mon, 14 May 2018 09:14:38 -0700
- Subject: Re: [PATCH] i386: Replace PREINIT_FUNCTION@PLT with *%eax in call
- References: <20180512133145.GA30506@gmail.com> <20180514154649.GB31160@mailbox.org>
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.