(gdb) disassemble fopen
Dump of assembler code for function _IO_new_fopen:
   0x00007ffff7a82f65 <+5>:     jmpq   0x7ffff7a82eb0 <__fopen_internal>
End of assembler dump.
(gdb) disassemble __fopen_internal
Dump of assembler code for function __fopen_internal:
   0x00007ffff7a82ec8 <+24>:    callq  0x7ffff7a33410 <memalign@plt>
   0x00007ffff7a82ef8 <+72>:    callq  0x7ffff7a90760 <_IO_no_init>
   0x00007ffff7a82f0e <+94>:    callq  0x7ffff7a8e640 <_IO_new_file_init>
   0x00007ffff7a82f1f <+111>:   callq  0x7ffff7a8e920 <_IO_new_file_fopen>
   0x00007ffff7a82f40 <+144>:   callq  0x7ffff7a8f510 <__GI__IO_un_link>
   0x00007ffff7a82f48 <+152>:   callq  0x7ffff7a33470 <free@plt+48>
End of assembler dump.