linux - LD_PRELOAD causing segmentation fault in dynamic library loader -

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i have written library intended loaded via ld_preload. on linux systems, causing dynamic library loader segfault during initialisation.

i have simple test case exhibits behaviour, if link -lm. 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 strange thing libm.so seems included in both versions: ldd shows same set of libraries, in 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 ld_debug, points libm.so part of 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] /lib64/libm.so.6 [0]: normal symbol `fma' [glibc_2.2.5] segmentation fault (core dumped)

unfortunately machines can reproduce problem on don't appear have debug symbols dynamic library loader available (and don't have administrative permissions), gdb doesn't yield 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 ()    /lib64/ld-linux-x86-64.so.2 #4  0x00007fff7fde18a3 in dl_main () /lib64/ld-linux-x86-64.so.2 #5  0x00007fff7fdf3a0e in _dl_sysdep_start () /lib64/ld-linux-x86-64.so.2 #6  0x00007fff7fddf4a4 in _dl_start () /lib64/ld-linux-x86-64.so.2 #7  0x00007fff7fddeb08 in _start () /lib64/ld-linux-x86-64.so.2 #8  0x0000000000000001 in ?? () #9  0x00007fffffffde01 in ?? () #10 0x0000000000000000 in ?? ()

what's best way go finding root cause of problem?

you can upload own dynamic loader built symbols , call link app, like:

∞ /lib/ld-linux-x86-64.so.2 /bin/echo linked linked


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