+++ This bug was initially created as a clone of Bug #14831 +++ Using the audit mechanism to redirect library lookups by implementing la_objsearch and returning a library that depends on libm.so (or libm.so itself) results in a subsequent segfault in the loader. I have attempted to create a standalone testcase, but did not succeed (I suspect the bug has to do with how IRELATIVE relocations are processed, but a simple testcase with IRELATIVE reloc works fine). Attaching a small testcase that depends on libm.so (and assumes it has IRELATIVE relocations). $ gdb --args /tmp/glibc-build/elf/ld.so --audit ./libaudit.so ./main GNU gdb (GDB) 7.4.1 (gdb) r Starting program: /tmp/glibc-build/elf/ld.so --audit ./libaudit.so ./main warning: Could not load shared library symbols for linux-vdso.so.1. Do you need "set solib-search-path" or "set sysroot"? Program received signal SIGSEGV, Segmentation fault. _dl_profile_fixup (l=0x7ffff7a33508, reloc_arg=4, retaddr=140737345060825, regs=0x7fffffffd1b0, framesizep=0x7fffffffd508) at ../elf/dl-runtime.c:176 176 DL_FIXUP_VALUE_TYPE value = *resultp; (gdb) bt #0 _dl_profile_fixup (l=0x7ffff7a33508, reloc_arg=4, retaddr=140737345060825, regs=0x7fffffffd1b0, framesizep=0x7fffffffd508) at ../elf/dl-runtime.c:176 #1 0x0000555555568306 in _dl_runtime_profile () at ../sysdeps/x86_64/dl-trampoline.h:48 #2 0x00007ffff7757fd9 in ?? () #3 0x00007fffffffd650 in ?? () #4 0x000055555555f5d1 in elf_machine_lazy_rel (skip_ifunc=<optimized out>, reloc=0x7ffff773e210, l_addr=140737344933888, map=0x7ffff7a33508) at ../sysdeps/x86_64/dl-machine.h:535 #5 elf_dynamic_do_Rela (skip_ifunc=<optimized out>, lazy=<optimized out>, nrelative=<optimized out>, relsize=<optimized out>, reladdr=<optimized out>, map=0x7ffff7a33508) at do-rel.h:85 #6 _dl_relocate_object (scope=0x7ffff7a33860, reloc_mode=<optimized out>, consider_profiling=1, consider_profiling@entry=0) at dl-reloc.c:265 #7 0x0000555555557ad2 in dl_main (phdr=<optimized out>, phdr@entry=0x555555554040, phnum=4160734848, phnum@entry=7, user_entry=user_entry@entry=0x7fffffffd7d8, auxv=0x555555777801) at rtld.c:2299 #8 0x0000555555568afc in _dl_sysdep_start (start_argptr=start_argptr@entry=0x7fffffffd890, dl_main=dl_main@entry=0x555555555ae0 <dl_main>) at ../elf/dl-sysdep.c:242 #9 0x0000555555558d0e in _dl_start_final (arg=0x7fffffffd890) at rtld.c:337 #10 _dl_start (arg=0x7fffffffd890) at rtld.c:563 #11 0x00005555555555a8 in _start () from /tmp/glibc-build/elf/ld.so (gdb) p l.l_reloc_result $1 = (struct reloc_result *) 0x0 (gdb) f 4 #4 0x000055555555f5d1 in elf_machine_lazy_rel (skip_ifunc=<optimized out>, reloc=0x7ffff773e210, l_addr=140737344933888, map=0x7ffff7a33508) at ../sysdeps/x86_64/dl-machine.h:535 535 value = ((ElfW(Addr) (*) (void)) value) (); (gdb) list 530 } 531 else if (__builtin_expect (r_type == R_X86_64_IRELATIVE, 0)) 532 { 533 ElfW(Addr) value = map->l_addr + reloc->r_addend; 534 if (__builtin_expect (!skip_ifunc, 1)) 535 value = ((ElfW(Addr) (*) (void)) value) (); 536 *reloc_addr = value; 537 } 538 else 539 _dl_reloc_bad_type (map, r_type, 1); (gdb) This patch fixes the crash --- diff --git a/elf/dl-reloc.c b/elf/dl-reloc.c index e6968a4..e3c8b26 100644 --- a/elf/dl-reloc.c +++ b/elf/dl-reloc.c @@ -262,8 +262,6 @@ _dl_relocate_object (struct link_map *l, struct r_scope_elem *scope[], #include "dynamic-link.h" - ELF_DYNAMIC_RELOCATE (l, lazy, consider_profiling, skip_ifunc); - #ifndef PROF if (__builtin_expect (consider_profiling, 0)) { @@ -290,6 +288,8 @@ _dl_relocate_object (struct link_map *l, struct r_scope_elem *scope[], } } #endif + + ELF_DYNAMIC_RELOCATE (l, lazy, consider_profiling, skip_ifunc); } /* Mark the object so we know this work has been done. */ --- However it causes tst-audit2 failure: {abcdef72, d8675309} != {d8675309, abcdef72} This test is added from: http://www.sourceware.org/ml/libc-alpha/2005-09/msg00075.html http://www.sourceware.org/ml/libc-alpha/2006-03/msg00138.html From ELF_DYNAMIC_RELOCATE we call elf_machine_rela, which calls CHECK_STATIC_TLS, which eventually allocates the static TLS *before* the first call to any malloc-esque hooks. That means we can't audit IFUNC resolver functions because of this ordering issue.