c - gdb giving a function name followed by a number instead of file and line number -

i have segmentation fault in program, , i'm using gdb identify it's happening. however, not able see clear line number error occurring.

below screenshot of output.

program received signal sigsegv, segmentation fault. [switching thread 20065168 (lwp 4645)] 0x007e537f in _int_free () /lib/libc.so.6 (gdb) backtrace #0  0x007e537f in _int_free () /lib/libc.so.6 #1  0x007e90f0 in free () /lib/libc.so.6 #2  0x080d9e67 in crypto_free () #3  0xbfd15f7c in ?? () #4  0xbfd16108 in ?? () #5  0x08070b3e in function_random.19532 () #6  0x00000001 in ?? () #7  0x00000000 in ?? () (gdb) 

frame 5 piece of code have written, don't quite understand means.

can please explain?

most likely, in case, debug symbols not present in binary. why, gdb not able read debugging info , display them.

re-compile code, debugging enabled.

example: gcc, use -g options.