[PATCH] Use libc_hidden_proto / _def for hidden wchar ifunc symbols.

[Stefan Liebler]

On 11/13/2017 02:58 PM, H.J. Lu wrote:
> On Mon, Nov 13, 2017 at 3:55 AM, Florian Weimer <fweimer@redhat.com> wrote:
>> On 11/13/2017 11:16 AM, Stefan Liebler wrote:
>>>
>>> This patch adds the libc_hidden_proto / libc_hidden_def construct.
>>> Then the __GI_* symbols are the default-ifunc-variants which can be called
>>> without PLT.
>>
>>
>> attribute_hidden and *_hidden_{proto,def} conflict on some architectures.
>> You need to remove attribute_hidden as part of this change.
> 
> That is true.  On i686, a hidden IFUNC function inside libc.so must be compiled
> with -fPIC via PLT since EBX must be loaded with GOT first.   This
> isn't an issue
> for x86-64 since PLT uses PC-relative addressing.  In this case, we
> should remove
> hidden attribute, instead of using __GI_* symbols, if we sill want to use IFUNC
> inside libc.so.
On s390/s390x, just removing attribute_hidden in wchar.h is fine, too. 
Then r12 will be setup with the GOT-pointer and IFUNC will be used 
inside libc.so.

What was your original intention? Getting rid of "PLT" or "PLT and 
IFUNC" for calls inside libc.so?

> 
> Now I have question, is there a way to apply attribute_hidden to a function
> depending on architecture? For example, we remove attribute_hidden
> from __wcsnlen, __wcscat, __wcsncpy, __wcpncpy,  __wcschrnul in headers
> under include/.   For x86, we mark them hidden in a header file under
> sysdeps/x86?
I don't know if duplicating the wchar.h file is such a good idea.

Bye
Stefan