Function calls in my ifunc resolver crash due to unitialized PLT entries.

[Niels Möller]

nisse@lysator.liu.se (Niels Möller) writes:

> I'll try to reproduce. Or maybe Mark can tell you how to reproduce it?

Now I have reproduced the problem. I'm running on a x86_64 debian
gnu/linux system. Not the most recent glibc, it seems I have libc-2.19
(the debian package libc6:amd64, version 2.19-13, built from the
"eglibc" fork). But I think Mark used the real glibc-2.21.

Build nettle-3.1 using ./configure --enable-fat && make && make check.
Then run the test program

  $ cat dlopen-test.c
  #include <stdio.h>
  #include <stdlib.h>
  #include <dlfcn.h>
  
  int main (int argc, char *argv[])
  {
    void *handle;
  
    handle = dlopen (argv[1], RTLD_NOW);
    if (!handle)
      {
        fprintf (stderr, "%s\n", dlerror ());
        exit (EXIT_FAILURE);
      }
    dlclose (handle);
    exit (EXIT_SUCCESS);
  }
  $ ./dlopen-test ~/build/nettle-fat/libnettle.so 
  Segmentation fault

In gdb, it gets as far as

  Dump of assembler code for function _nettle_cpuid@plt:
  => 0x00007ffff7601b90 <+0>:	jmpq   *0x22c842(%rip)        # 0x7ffff782e3d8
     0x00007ffff7601b96 <+6>:	pushq  $0x26
     0x00007ffff7601b9b <+11>:	jmpq   0x7ffff7601920

But the address in that slot is not yet properly relocated,

  (gdb) x/gx 0x7ffff782e3d8
  0x7ffff782e3d8:	0x0000000000009b96

Regards,
/Niels

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