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[PATCH] PR ld/19636: [x86] Resolve undefweak and defined symbols in executable

H.J. Lu hjl.tools@gmail.com
Wed Feb 24 14:47:00 GMT 2016 
On Wed, Feb 24, 2016 at 6:45 AM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Tue, 23 Feb 2016, H.J. Lu wrote:
>
>> For i386 and x86-64, undefined weak and defined symbols are resolved
>> without dynamic relocation when creating executable.  Undefined weak
>> symbols aren't needed in the dynamic symbol table in executable.  One
>> exception is on i386, we need undefined weak symbols in the dynamic
>> symbol table in PIE if input relocatable files contain branchs without
>> PLT so that we can branch to 0 with dynamic relocation in text section.
>
> Um, wait.  Have you now changed it so that this program won't work anymore
> (no matter if PIC or non-PIC)?:

It never worked correctly:

https://sourceware.org/bugzilla/show_bug.cgi?id=19719

>   extern void undef() __attribute__((weak));
>   int main()
>   {
>     if (undef)
>       undef ();
>     return 0;
>   }
>
>> This makes behaviors of static excutable, dynamic excutable and position
>> independent executable consistent with references to undefined weak and
>> defined symbols, regardless if the relocatable input is compiled with
>> PIC or not.
>
> Because, while consistence is good, it's more important that the above
> program keeps working (and if only under PIC).
>

I will add

-z dynamic-undefined-weak   Treat undefined weak symbol as dynamic

to enable the old behavior.



-- 
H.J.
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