[Bug 945927] Re: ld incorrectly gives 'undefined reference'

[CF]

Hi Matthias,

I give up. It seems to me that you do not see my point (it's not about
indirect linkage, it's about delaying resolution of undefined symbols to
the final link).

I tested the gold linker, it work for the test case WITHOUT problem.
That'll be my solution.

Many thanks for your answers, though, they were elucidating in the end.

Christoph

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https://bugs.launchpad.net/bugs/945927

Title:
  ld incorrectly gives 'undefined reference'

Status in “binutils” package in Ubuntu:
  Invalid

Bug description:
  I had an unexpected link problem while trying to probe libraries in a
  configure script.

  I am using the latest update (2012-03-03 21:00 MEZ) of kubuntu 11.10, the binutils package is 2.21.53.20110810-0ubuntu5.1
  My machine is a  Intel(R) Core(TM)2 Duo CPU     E8400  @ 3.00GHz, but I doubt that matters.

   I was able to cook the problem down to the following.

  Situation:
  libfoo.so needs libm, and was created with -lm (ldd shows the dependency)
  libbar.so needs libm, but was not created with -lm (no ldd dependency)
  My program only needs libbar.so

  Problem:

  gcc prog.c -L. -lbar -lfoo -lm

  yields an 'undefined reference to sinh'
  If I run the link with -Wl,--trace-symbol=sinh, the linker actually reports that -lm contains sinh, but fails nevertheless.

  What works is
  gcc prog.c -L. -lbar -lm
  gcc prog.c -L. -lbar -lm -lfoo

  [The example of course cries for a simple workaround by reordering the
  libs, but this is a mess when you try it in the configure. So just
  take the lib ordering for granted (and this configure works on dozens
  of other systems). I also know that libbar isn't up to the standards -
  but, in real life, I won't change the way how other packages create
  their shared libs.]

  Here's some simple C files to reproduce the bug
  --- a.c:
  #include <math.h>
  double foo (double x) { return exp(x); }
  ---- b.c:
  #include <math.h>
  double bar(double x) { return sinh(x); }
  ---- c.c:
  double bar (double);
  int main ()
  {
     double x = bar (1.);
  }
  ---
  gcc -fPIC -c a.c
  gcc -shared -fPIC a.o -o libfoo.so
  gcc -fPIC -c b.c
  gcc -shared -fPIC b.o -o libbar.so

  gcc c.c -L. -lbar -lfoo -lm

  ProblemType: Bug
  DistroRelease: Ubuntu 11.10
  Package: binutils 2.21.53.20110810-0ubuntu5.1
  ProcVersionSignature: Ubuntu 3.0.0-16.28-generic 3.0.17
  Uname: Linux 3.0.0-16-generic x86_64
  ApportVersion: 1.23-0ubuntu4
  Architecture: amd64
  Date: Sat Mar  3 23:08:39 2012
  InstallationMedia: Kubuntu 10.04.1 LTS "Lucid Lynx" - Release amd64 (20100816.2)
  ProcEnviron:
   LANGUAGE=
   PATH=(custom, user)
   LANG=de_DE.UTF-8
   SHELL=/bin/tcsh
  SourcePackage: binutils
  UpgradeStatus: Upgraded to oneiric on 2012-02-29 (3 days ago)

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