Linux ELF OS ABI

[H.J. Lu]

On Thu, Feb 18, 2010 at 1:57 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Thu, Feb 18, 2010 at 1:43 PM, Doug Semler <dougsemler@gmail.com> wrote:
>> I have a shared object that I compile on one machine (Fedora 12) and
>> run on another (CentOS5 or Ubuntu 8.04) machine.  Things were fine
>> (ensuring that we only used older APIs) running this way until
>> recently.  Recent compiles on the Fedora 12 machine started tagging
>> the shared libraries being built with the GNU/Linux ABI rather than
>> the Unknown (SYSV) ABI.  The problem seems to be that on the older
>> machines, the shared object loader can't parse this (i get an ELF file
>> OS ABI invalid shared object when trying to load the .so file from an
>> executable).  An executable tagged with the GNU/Linux ABI type runs
>> perfectly fine.  I *think* the problems started when I updated the
>> glibc to 2.11.2 on the Fedora system.
>>
>> What is weird is that if I link the shared object with --strip-all it
>> will not work.  If I then strip the shared object with strip, it is
>> loadable.  The only difference between the two shared object files is
>> the ELF OS ABI (byte 8), otherwise they are the same.
>>
>> Is there a way to find out which symbol is causing this ABI to be
>> selected?  It looks like there is a function in elf.c that asks if
>> there are any symbols of type STT_GNU_IFUNC.  How can I find out what
>> symbols are of this type?
>>
>> Additionally, I would have expected the output from strip to keep this
>> if it was necessary, which makes it seem as if there is something
>> funny going on in the linker...
>>
>> It seems that what I do should be supported...even a simple program
>> that has the following seems that it should run on older systems, but
>> it doesn't.  Or am I completely whacked and have to keep an older
>> system around so that I can compile for that system (which seems
>> silly).
>>
>>  shared.c  -  compile into shared library
>>  ----
>>  int foo()
>>  {
>>    return 42;
>>  }
>>
>>  main.c - compile and link against shared library
>>  ----
>>  extern int foo();
>>  int main()
>>  {
>>    return foo();
>>  }
>>
>
> I think linker should mark Linux OS ABI only if there is an IFUNC
> definition. Please open a bug report.
>

It has been fixed:

http://sourceware.org/ml/binutils-cvs/2010-02/msg00138.html

You may want to open a Fedora bug to request backporting this fix.

Thanks.

-- 
H.J.