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From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Mon, 07 Nov 2016 17:14:00 -0000
Message-ID: <CAMe9rOqWq--vo3T8NhEpFGuyA7Z8hHVN_DK6g8rauVaxYKZ+ig@mail.gmail.com>
Subject: Re: [PATCH] Don't use PLT nor GOT in libc.a [BZ #20750]
To: Florian Weimer <fweimer@redhat.com>
Cc: GNU C Library <libc-alpha@sourceware.org>
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On Mon, Nov 7, 2016 at 8:03 AM, Florian Weimer <fweimer@redhat.com> wrote:
> On 11/04/2016 08:25 PM, H.J. Lu wrote:
>>
>> On Fri, Nov 4, 2016 at 12:03 PM, Florian Weimer <fweimer@redhat.com>
>> wrote:
>>>
>>> On 11/04/2016 06:47 PM, H.J. Lu wrote:
>>>>
>>>>
>>>> There is no need to use PLT nor GOT in libc.a to branch to a function,
>>>> regardless whether libc.a is compiled with PIC or not.
>>>>
>>>> Tested on x86-64.  OK for master?
>>>
>>>
>>>
>>> Isn't this header file used outside of libc as well?
>>
>>
>> It is used for other .a files.  If they aren't used to create static
>> binaries,
>> PLT/GOT may be used.  The resulting executable will work correctly.
>
>
> You mean because =E2=80=9Cname=E2=80=9D is automatically mapped to =E2=80=
=9Cname@plt=E2=80=9D?

No.  There is no "@plt".  Linker will create a PLT entry if the function
is defined in a shared object.

> I find this comment not very illuminating:
>
> +/* For libc.a, we want to branch to target directly.  */
>  # define JUMPTARGET(name)      name
>
> And cheating the static linker in this way seems like a future maintenance
> hazard.
>

It is ok as long as those static archives aren't used to create shared
objects.

--=20
H.J.