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I'm aware that it is possible to use readelf -d <elf> | grep RPATH to inspect a given binary from the shell, but is it possible to do this within a process?

Something like (my completely made up system call):

  /* get a copy of current rpath into buffer */
  sys_get_current_rpath(&buffer);

I'm trying to diagnose some suspect SO linking issues in our codebase, and would like to inspect the RPATH this way if possible (I'd rather not have to spawn an external script).

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1
  • 5
    Keep in mind that when diagnosing shared library issues you should also inspect the RUNPATH tag. Thus you should grep PATH instead. It's up to the linker whether RPATH or RUNPATH is used, and there are subtle but important differences between the two: stackoverflow.com/a/52020177
    – Nicolas Capens
    Commented Aug 28, 2020 at 13:55

6 Answers 6

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196

For the record, here are a couple of commands that will show the rpath / runpath header.

objdump -x binary-or-library |grep 'R.*PATH'

Maybe an even better way to do it is the following:

readelf -d binary-or-library |head -20

The second command also lists the direct dependencies on other libraries followed by rpath.

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67

The question is specifically about RPATH, but modern linkers use RUNPATH instead. See this answer -- there is a subtle semantic difference between the two.

The answer is updated to print either.

#include <assert.h>
#include <stdio.h>
#include <elf.h>
#include <link.h>

int main()
{
  const ElfW(Dyn) *dyn = _DYNAMIC;
  const ElfW(Dyn) *rpath = NULL;
  const ElfW(Dyn) *runpath = NULL;
  const char *strtab = NULL;
  for (; dyn->d_tag != DT_NULL; ++dyn) {
    if (dyn->d_tag == DT_RPATH) {
      rpath = dyn;
    } else if (dyn->d_tag == DT_RUNPATH) {
      runpath = dyn;
    } else if (dyn->d_tag == DT_STRTAB) {
      strtab = (const char *)dyn->d_un.d_val;
    }
  }

  assert(strtab != NULL);

  if (rpath != NULL) {
    printf("RPATH: %s\n", strtab + rpath->d_un.d_val);
  } else if (runpath != NULL) {
    printf("RUNPATH: %s\n", strtab + runpath->d_un.d_val);
  }
  return 0;
}
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  • 2
    it is brilliant, but it does not work with $ORIGIN. $ORIGIN is not interpreted, and returned as is by the function. Is there a way to add the $ORIGIN interpretation?
    – Jérôme
    Commented Jul 10, 2014 at 15:30
  • 7
    @Jérôme If you are executing in an environment where /proc is mounted, then expanding $ORIGIN is as simple as readlink("/proc/self/exe", ...) then NUL-terminate at the last slash.
    – Employed Russian
    Commented Jul 11, 2014 at 16:09
  • 1
    While the question was specifically about RPATH, I'd like to note that it's equally important to check the DT_RUNPATH tag if one wishes to know the paths a binary might be loading its shared libraries from.
    – Nicolas Capens
    Commented Aug 28, 2020 at 13:57
21

You can also use:

chrpath -l binary-or-library
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  • 1
    On ubuntu: apt-get install -y chrpath
    – levzettelin
    Commented Sep 6, 2020 at 11:38
5

Here's what I use for convenience, as a shell function:

function getrpath {
    eu-readelf -d "${1:?}" | sed -e '/RUNPATH/{s~.*\[\(.*\)\]~\1~;n};d'
}

This consumes eu-readelf output from elfutils like:

Type              Value
NEEDED            Shared library: [libpq.so.5]
NEEDED            Shared library: [libc.so.6]
RUNPATH           Library runpath: [/some/path/to/lib]
....

and emits

 /some/path/to/lib

It should work fine with binutils readelf instead of elfutils eu-readelf too.

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2

If you have patchelf it can also print rpath in a pretty format:

> patchelf --print-rpath /path/to/elf
$ORIGIN:$ORIGIN/../../lib
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1

There is a way. Follow the example code in man dlinfo [1], but use NULL as the first parameter of dlopen().

[1] https://man7.org/linux/man-pages/man3/dlinfo.3.html

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