How to check what shared libraries are loaded at run time for a given process?

Question

Is there a way to check which libraries is a running process using?

To be more specific, if a program loads some shared libraries using dlopen, then readelf or ldd is not going to show it. Is it possible at all to get that information from a running process? If yes, how?

Answer 1

Other people are on the right track. Here are a couple ways.

cat /proc/NNNN/maps | awk '{print $6}' | grep '\.so' | sort | uniq

Or, with strace:

strace CMD.... 2>&1 | grep -E '^open(at)?\(.*\.so'

Both of these assume that shared libraries have ".so" somewhere in their paths, but you can modify that. The first one gives fairly pretty output as just a list of libraries, one per line. The second one will keep on listing libraries as they are opened, so that's nice.

And of course lsof...

lsof -p NNNN | awk '{print $9}' | grep '\.so'

Answer 2

May be lsof - the swiss army knife of linux will help?

edit: to run, lsof -p <pid>, lists all sorts of useful information, for example, if the process is java, lists all the open jars - very cool...

Answer 3

Actually, you can do this in your code in the following way:

#include <link.h>

using UnknownStruct = struct unknown_struct {
   void*  pointers[3];
   struct unknown_struct* ptr;
};
using LinkMap = struct link_map;

auto* handle = dlopen(NULL, RTLD_NOW);
auto* p = reinterpret_cast<UnknownStruct*>(handle)->ptr;
auto* map = reinterpret_cast<LinkMap*>(p->ptr);

while (map) {
  std::cout << map->l_name << std::endl;
  // do something with |map| like with handle, returned by |dlopen()|.
  map = map->l_next;
}

The link_map structure contains at least the base address and the absolute file name. It's the structure that is actually returned by dlopen() with non-NULL first argument. For more details see here.

Answer 4

ltrace seems to be your friend.

From ltrace manual:

ltrace is a program that simply runs the specified command until it exits. It intercepts and records the dynamic library calls which are called by the executed process and the signals which are received by that process. It can also intercept and print the system calls exe‐ cuted by the program.

       Its use is very similar to strace(1).

Answer 5

On Linux, /proc/<processid>/maps contains a list of all the files mapped into memory, which I believe should include any loaded by dlopen().

Answer 6

On solaris there is also the pldd command.

Answer 7

You can do so programmatically on Linux. You can use the function dl_iterate_phdr.

Here is a small example taken from the man page :

#define _GNU_SOURCE
#include <link.h>
#include <stdlib.h>
#include <stdio.h>

static int
callback(struct dl_phdr_info *info, size_t size, void *data)
{
    int j;

   printf("name=%s (%d segments)\n", info->dlpi_name,
        info->dlpi_phnum);

   for (j = 0; j < info->dlpi_phnum; j++)
         printf("\t\t header %2d: address=%10p\n", j,
             (void *) (info->dlpi_addr + info->dlpi_phdr[j].p_vaddr));
    return 0;
}

int
main(int argc, char *argv[])
{
    dl_iterate_phdr(callback, NULL);

   exit(EXIT_SUCCESS);
}

Answer 8

Would strace trace the library file being opened?

Answer 9

The question is whether you want to know it about a foreign process:

$ sleep 1h&p=$!;sleep 0.1;gdb -p $p -batch -ex 'info shared'
[1] 637756
...
From                To                  Syms Read   Shared Object Library
0x00007f795ffc4700  0x00007f7960135aed  Yes         /lib64/libc.so.6
0x00007f79601cc0a0  0x00007f79601f2d35  Yes         /lib64/ld-linux-x86-64.so.2
[Inferior 1 (process 637756) detached]

Or about your own process:

#include <iostream>
#include <link.h>
#include <cassert>
#include <dlfcn.h>
int main() {
  // prevent R_X86_64_COPY and r_state inconsistency if we accessed "_r_debug" directly.
  r_debug *debug = (r_debug *) dlsym(RTLD_DEFAULT, "_r_debug");
  assert(debug);
  assert(debug->r_version == 1);
  assert(debug->r_state == r_debug::RT_CONSISTENT);
  link_map *prev = NULL;
  for (link_map *map = debug->r_map; map; prev = map, map = map->l_next) {
    assert(map->l_prev == prev);
    std::cout << map << " " << (!map->l_name[0] ? "<empty>" : map->l_name) << std::endl;
  }
}