The background of the issue is in an already answered question, here
I have a symbol that I want to use in a shared library but despite being listed as a T defined symbol via nm, F (function) via objdump, when I try to access it using dlopen() or via Python (ctypes.CDLL), it seemingly does not exist or is not defined.
I was reading here that this could be related to dependencies.
Output of ldd:
linux@host:~$ ldd ./compiled_program
linux-vdso.so.1 (0x00007ffde1fdf000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f3381e7c000)
/lib64/ld-linux-x86-64.so.2 (0x00007f338246f000)
Output of dn -DC:
linux@host:~$ nm -DC ./compiled_program
w _ITM_deregisterTMCloneTable
w _ITM_registerTMCloneTable
w __cxa_finalize
w __gmon_start__
U __libc_start_main
U __stack_chk_fail
U printf
U putchar
U puts
U rand
U srand
U time
With my limited knowlege of C, I am unable to tell if any of these might be unresolved dependencies and where to look for which libraries to load, as the answer suggests, to include them. Is it as simple as finding the library and adding an #include <...> or do I have to locate the library and load it with dlopen()? The answer seems to suggest the latter. I appreciate that I am completely flailing in the dark here!
My current dlopen code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dlfcn.h>
int main(int argc, char** argv) {
void *handle;
void (*func_in_question)(const char*);
handle = dlopen("./compiled_program", RTLD_LAZY);
if (!handle) {
/* fail to load the library */
fprintf(stderr, "Error: %s\n", dlerror());
return EXIT_FAILURE;
}
*(void**)(&func_in_question) = dlsym(handle, "function_I_would_like_to_use");
if (!func_in_question) {
/* no such symbol */
fprintf(stderr, "Error: %s\n", dlerror());
dlclose(handle);
return EXIT_FAILURE;
}
func_in_question(argv[1]);
dlclose(handle);
return EXIT_SUCCESS;
}
comes back with the undefined symbol error.
I would be grateful for any pointers on, a) any other reasons why I might not be able to access this symbol? and b) if my half-baked suspicion about dependencies is anywhere near to making sense!
EDIT: copying error message from original question linked above:
Error: ./compiled_program: undefined symbol: function_I_would_like_to_use
and the output of nm --defined-only ./compiled_program from original
question:
0000000000200d98 d _DYNAMIC 0000000000200f88 d _GLOBAL_OFFSET_TABLE_ 0000000000000ba0 R _IO_stdin_used 0000000000000d64 r __FRAME_END__ 0000000000000bfc r __GNU_EH_FRAME_HDR 0000000000201010 D __TMC_END__ 0000000000201010 B __bss_start 0000000000201000 D __data_start 00000000000007d0 t __do_global_dtors_aux 0000000000200d90 t __do_global_dtors_aux_fini_array_entry 0000000000201008 D __dso_handle 0000000000200d88 t __frame_dummy_init_array_entry 0000000000200d90 t __init_array_end 0000000000200d88 t __init_array_start 0000000000000b90 T __libc_csu_fini 0000000000000b20 T __libc_csu_init 0000000000201010 D _edata 0000000000201018 B _end 0000000000000b94 T _fini 0000000000000660 T _init 0000000000000710 T _start 0000000000201010 b completed.7696 0000000000201000 W data_start 0000000000000740 t deregister_tm_clones 0000000000000810 t frame_dummy 0000000000000a92 T main 000000000000081a T function_I_would_like_to_use \\ << this one 0000000000000780 t register_tm_clones
