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linuxgccassemblyldbinutils

ELF Relocation - where came from these symbols?

In my Debian x86 32 Bits, when I do readelf -r /usr/lib/libstdc++.so.6 | grep pthread, I get this output:

000eceac  00006206 R_386_GLOB_DAT    00000000   pthread_cancel
000ed058  00000807 R_386_JUMP_SLOT   00000000   pthread_cond_destroy
000ed148  00001207 R_386_JUMP_SLOT   00000000   pthread_cond_signal
000ed1e8  00001e07 R_386_JUMP_SLOT   00000000   pthread_key_create
000ed320  00002a07 R_386_JUMP_SLOT   00000000   pthread_once
000ed418  00003607 R_386_JUMP_SLOT   00000000   pthread_getspecific
000ed42c  00003a07 R_386_JUMP_SLOT   00000000   pthread_mutex_unlock
000ed4ec  00004607 R_386_JUMP_SLOT   00000000   pthread_create
000ed54c  00004b07 R_386_JUMP_SLOT   00000000   pthread_equal
000ed678  00005607 R_386_JUMP_SLOT   00000000   pthread_mutex_lock
000ed71c  00006007 R_386_JUMP_SLOT   00000000   pthread_cond_wait
000ed7b0  00006907 R_386_JUMP_SLOT   00000000   pthread_key_delete
000ed8b4  00007307 R_386_JUMP_SLOT   00000000   pthread_cond_broadcast
000ed8c0  00007507 R_386_JUMP_SLOT   00000000   pthread_detach
000ed8f0  00007a07 R_386_JUMP_SLOT   00000000   pthread_setspecific
000ed968  00007c07 R_386_JUMP_SLOT   00000000   pthread_join

however when I list the dependencies of /usr/lib/libstdc++.so.6 libpthread isn't listed:

john@ThirdEarth:~$ ldd /usr/lib/libstdc++.so.6
linux-gate.so.1 =>  (0xb77df000)
libm.so.6 => /lib/i686/cmov/libm.so.6 (0xb76ad000)
libc.so.6 => /lib/i686/cmov/libc.so.6 (0xb7566000)
/lib/ld-linux.so.2 (0xb77e0000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0xb7547000)

so how these dependencies are resolved by the dynamic loader? I found a similar issue with __gmon_start__ where, roughly speaking, is the definition of this symbol?

Solution

  • The pthread functions in Linux are implemented in libc.

    For example, on a system that I had to hand:

    objdump -T /lib/libc-2.11.1.so | grep pthread

    gives

    00000000000f64a0 g    DF .text  0000000000000026  GLIBC_2.3.2 pthread_cond_signal
0000000000126100 g    DF .text  0000000000000026 (GLIBC_2.2.5) pthread_cond_signal
00000000000f6be0 g    DF .text  000000000000005a  GLIBC_PRIVATE __libc_pthread_init
00000000000f65f0 g    DF .text  0000000000000026  GLIBC_2.2.5 pthread_mutex_lock
00000000000f63e0 g    DF .text  0000000000000026  GLIBC_2.2.5 pthread_condattr_init
00000000000f6290 g    DF .text  0000000000000026  GLIBC_2.2.5 pthread_attr_getschedparam
...