How to undo strip - i.e. add symbols back to stripped binary

Question

I have a stripped binary and symbol-file. Is it possible to add the symbols back to binary and create an unstripped binary.

My use-case is using this binary w/ valgrind.

i'd say recompile, can't think of anything else :) – mata Apr 12 '13 at 18:08 — mata, Apr 12 '13 at 18:08

score 17 · Answer 1 · edited May 23 '17 at 12:25

For those tools that do not support separate files for debug information, you can glue the debug sections back to the original binary.

You can do something along these lines, for example:

First build a small program that efficiently extracts an arbitrary chunk from a file

(note that dd will not do this efficiently as we'd have to use bs=1 to support an arbitrary offset and length, and objcopy -O binary does not copy sections that are not ALLOC, LOAD※)

cat <<EOF | gcc -xc -o ./mydd -
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <unistd.h>
#include <macros.h>

char buf[1024*1024];

int main(int argc, char** argv) {
  char    *fin, *fout;
  int     fdin, fdout;
  off_t   off;
  size_t  len;
  ssize_t rd;
  int     status;

  if (argc != 5) {
    fprintf(stderr, "Usage: %s fin skip count fout\n", argv[0]);
    return 1;
  }

  fin   = argv[1];
  off   = strtoul(argv[2], NULL, 0);
  len   = strtoul(argv[3], NULL, 0);
  fout  = argv[4];
  fdin  = -1;
  fdout = -1;

  if ((fdin  = open(fin,  O_RDONLY)) < 0) {
    status = errno;
    perror(fin);
  } else if ((fdout = open(fout, O_WRONLY|O_TRUNC|O_CREAT, 0660)) < 0) {
    status = errno;
    perror(fout);
  } else if (lseek(fdin, off, SEEK_SET) == (off_t)-1) {
    status = errno;
    perror("Seeking input");
  } else {
    while (len > 0 && (rd = read(fdin, buf, min(len, sizeof(buf)))) > 0) {
      if (write(fdout, buf, rd) != rd) {
        /*don't bother with partial writes or EINTR/EAGAIN*/
        status = errno;
        perror(fin);
        break;
      }
      len -= rd;
    }
    if (rd < 0) {
      status = errno;
      perror(fin);
    }
  }
  if (fdin >= 0)  close(fdin);
  if (fdout >= 0) close(fdout);
  return status;
}
EOF

Finally, extract the .debug sections and glue them to the stripped binary.

objcopy `
    objdump -h program.dbg  |
    awk '$2~/^\.debug/' |
    while read idx name size vma lma off algn ; do
        echo "$name" >&2
        echo " --add-section=$name=$name.raw"
        ./mydd program.dbg 0x$off 0x$size $name".raw"
    done
` program program_with_dbg

dd can seek to an arbitrary address without shrinking the blocksize to 1. See flag "skip_bytes" in dd's man. — Narcolessico, Apr 23 '18 at 11:43
Note that this doesn't copy the relocations associated with the sections — Tavian Barnes, May 14 '21 at 20:58

score 8 · Answer 2 · answered Feb 28 '18 at 17:59

8

elfutils comes with the tool eu-unstrip which can be used to merge symbol files with executables. The result can then be used in place of the stripped version.

answered Feb 28 '18 at 17:59

the8472

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For anyone else that made the same mistake as myself, the man page is not the best and an interesting decision was made. "The first form puts the result in DEBUG-FILE if -o was not given." If you just provide the stripped from .so file, followed by the stripped to .so.debug file, the ultimate result is placed into the .so.debug file. I think it's safe to say almost anyone would expect the combined symbols to go back into the stripped from .so file. Or maybe their use of 'STRIPPED-FILE' is ambiguous as to 'stripped from' or 'stripped into'? – JoeManiaci Jul 22 '22 at 19:30
1

For reference: `eu-unstrip binary binary.dbg` : binary.dbg now has both the binary and debug symbols – Étienne Jan 26 '23 at 15:22

score 5 · Accepted Answer · edited May 23 '17 at 10:31

5

Valgrind supports separate debug files, so you should use the answer here, and valgrind should work properly with the externalized debug file.

edited May 23 '17 at 10:31

Community

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answered Apr 12 '13 at 18:25

Anya Shenanigans

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And no: you can't create an unstripped binary from a stripped one (at least not easily). But you shouldn't need to, as this answer correctly states. – Employed Russian Apr 12 '13 at 18:49
I am sorry, but it is unclear how can I use this debug file w/ valgrind. Would appreciate any pointers. – cached Apr 12 '13 at 19:32
The directions provided in the "answer here" appear to be quite clear. You build the separate debuginfo, and then Valgrind and GDB will automagically load them. – Employed Russian Apr 12 '13 at 19:41
Thanks - will give it a stry. – cached Apr 12 '13 at 19:55

How to undo strip - i.e. add symbols back to stripped binary

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