Re: Linux ELF OS ABI

["H.J. Lu" <hjl dot tools at gmail dot com>]

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.