LD_PRELOAD raises a segmentation fault in the dynamic library loader

I wrote a library for loading via LD_PRELOAD

. On some Linux systems, this causes the dynamic link library to be loaded during initialization.

I have a simple test case that demonstrates this behavior, but only if I link to -lm

. For example:

# Works fine
gcc -o vecadd.normal -std=c99 vecadd.c -lOpenCL
LD_PRELOAD=/path/to/my/library.so ./vecadd.normal

# Causes segmentation fault
gcc -o vecadd.broken -std=c99 vecadd.c -lOpenCL -lm
LD_PRELOAD=/path/to/my/library.so ./vecadd.broken

      

        
        
        
      

    

The weird thing is that it libm.so

seems to be included in both versions: it ldd

shows exactly the same set of libraries, only in a different order:

vecadd.normal:
  linux-vdso.so.1 =>  (0x00007fffed9ff000)
  libOpenCL.so => /usr/lib64/libOpenCL.so (0x00007f135c9b1000)
  libc.so.6 => /lib64/libc.so.6 (0x00007f135c61c000)
  libdl.so.2 => /lib64/libdl.so.2 (0x00007f135c418000)
  libnuma.so.1 => /usr/lib64/libnuma.so.1 (0x00007f135c20f000)
  libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00007f135bf08000)
  libm.so.6 => /lib64/libm.so.6 (0x00007f135bc84000)
  libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f135ba6e000)
  /lib64/ld-linux-x86-64.so.2 (0x00007f135cbd4000)
vecadd.broken:
  linux-vdso.so.1 =>  (0x00007fff25c74000)
  libOpenCL.so => /usr/lib64/libOpenCL.so (0x00007fb8c071e000)
  libm.so.6 => /lib64/libm.so.6 (0x00007fb8c0499000)
  libc.so.6 => /lib64/libc.so.6 (0x00007fb8c0105000)
  libdl.so.2 => /lib64/libdl.so.2 (0x00007fb8bff01000)
  libnuma.so.1 => /usr/lib64/libnuma.so.1 (0x00007fb8bfcf7000)
  libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00007fb8bf9f1000)
  libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007fb8bf7db000)
  /lib64/ld-linux-x86-64.so.2 (0x00007fb8c0941000)

      

        
        
        
      

    

Google directed me to LD_DEBUG

, which also points out libm.so

as part of the problem:

 14143: symbol=fma;  lookup in file=./vecadd.broken [0]
 14143: symbol=fma;  lookup in file=/path/to/my/library.so [0]
 14143: symbol=fma;  lookup in file=/usr/lib64/libOpenCL.so [0]
 14143: symbol=fma;  lookup in file=/lib64/libm.so.6 [0]
 14143: binding file /path/to/my/library.so [0] to /lib64/libm.so.6 [0]: normal symbol `fma' [GLIBC_2.2.5]
Segmentation fault (core dumped)

      

        
        
        
      

    

Unfortunately, the only machines I can reproduce this issue on do not have debug symbols for the loadable dynamic library loader (and I have no administrative permissions), so GDB brings nothing useful:

gdb ./vecadd.broken
(gdb) set environment LD_PRELOAD /path/to/my/library.so
(gdb) run
Starting program: vecadd.broken 

Program received signal SIGSEGV, Segmentation fault.
0x0000000000003dce in ?? ()
Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.132.el6_5.1.x86_64
(gdb) bt
#0  0x0000000000003dce in ?? ()
#1  0x00007fff7f755369 in ?? ()
#2  0x00007fffffffd840 in ?? ()
#3  0x00007fff7fde9e91 in _dl_relocate_object ()
   from /lib64/ld-linux-x86-64.so.2
#4  0x00007fff7fde18a3 in dl_main () from /lib64/ld-linux-x86-64.so.2
#5  0x00007fff7fdf3a0e in _dl_sysdep_start () from /lib64/ld-linux-x86-64.so.2
#6  0x00007fff7fddf4a4 in _dl_start () from /lib64/ld-linux-x86-64.so.2
#7  0x00007fff7fddeb08 in _start () from /lib64/ld-linux-x86-64.so.2
#8  0x0000000000000001 in ?? ()
#9  0x00007fffffffde01 in ?? ()
#10 0x0000000000000000 in ?? ()

      

        
        
        
      

    

How can you find the root cause of this problem?