Linux ELF OS ABI

[H.J. Lu]

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.

Thanks.


-- 
H.J.