--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/chrpath.c	Fri Jul 20 01:51:24 2012 +0200
@@ -0,0 +1,260 @@
+/*
+<URL:http://gcc.gnu.org/ml/gcc/1999-04n/msg01105.html>
+
+Re: changing embedded RPATH in existing executables.
+
+  To: geoffk@ozemail.com.au
+  Subject: Re: changing embedded RPATH in existing executables.
+  From: <peeter_joot@VNET.IBM.COM> (peeter joot)
+  Date: Fri, 30 Apr 1999 16:14:44 -0400 (EDT)
+  Cc: peeterj@ca.ibm.com, egcs@cygnus.com, libc-hacker@cygnus.com, linux-gcc@vger.rutgers.edu
+  Reply-To: <peeter_joot@VNET.IBM.COM>
+
+> _Changing_ is a little tricky, but the attached program strips rpaths
+> from executables (I find it essential for debugging the binutils).
+> It's endian-dependent, if you want this for x86 you can just change
+> the occurrences of 'MSB' to 'LSB' and compile (I should really fix
+> that).
+
+Hi Geoff,
+
+With your program as a guide (and some peeks into libbfd, elf.h, a bit
+of the glibc dynamic loader code, objdump, and a hex-editor) I was able to
+figure out enough to find and change the rpath string.  That was fun!
+
+This program assumes (unlike your original program) that there is only
+one DT_RPATH tag in the dynamic section as even with multiple '-Wl,-rpath,'
+commands in the link this seems to occur (they all get concatonated into
+a : separated path).
+
+Thanks for your help.  If you want to use this on non-x86 you have to change
+the occurances of LSB back to MSB:)
+
+Peeter
+--
+*/
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <elf.h>
+#if defined(HAVE_LINK_H)
+#  include <link.h>
+#endif /* HAVE_LINK_H */
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include "protos.h"
+
+/**
+ * Reads an ELF file, and reads or alters the RPATH setting.
+ *
+ * TODO:
+ *  modify to add RPATH setting if none exists.
+ */
+
+
+int
+chrpath(const char *filename, const char *newpath, int convert)
+{
+  int fd;
+  Elf_Ehdr ehdr;
+  int i;
+  Elf_Phdr phdr;
+  Elf_Shdr shdr;
+  Elf_Dyn *dyns;
+  int rpathoff;
+  char * strtab;
+  char * rpath;
+  unsigned int rpathlen;
+  int oflags;
+  int rpath_dyns_index;
+
+  if (NULL == newpath && 0 == convert)
+     oflags = O_RDONLY;
+  else
+     oflags = O_RDWR;
+
+  fd = elf_open(filename, oflags, &ehdr);
+  if (fd == -1)
+  {
+    perror ("elf_open");
+    return 1;
+  }
+
+   if (0 != elf_find_dynamic_section(fd, &ehdr, &phdr))
+   {
+     perror("found no dynamic section");
+     return 1;
+   }
+
+  dyns = malloc(phdr.p_filesz);
+  if (dyns == NULL)
+    {
+      perror ("allocating memory for dynamic section");
+      return 1;
+    }
+  memset(dyns, 0, phdr.p_filesz);
+  if (lseek(fd, phdr.p_offset, SEEK_SET) == -1
+      || read(fd, dyns, phdr.p_filesz) != (int)phdr.p_filesz)
+    {
+      perror ("reading dynamic section");
+      free(dyns);
+      return 1;
+    }
+
+  rpathoff = -1;
+  for ( rpath_dyns_index = 0; dyns[rpath_dyns_index].d_tag != DT_NULL;
+        ++rpath_dyns_index )
+    {
+      if ( elf_dynpath_tag(dyns[rpath_dyns_index].d_tag) )
+      {
+         rpathoff = dyns[rpath_dyns_index].d_un.d_ptr;
+         break;
+      }
+    }
+  if (rpathoff == -1)
+    {
+      printf("%s: no rpath or runpath tag found.\n", filename);
+      free(dyns);
+      return 2;
+    }
+
+  if (lseek(fd, ehdr.e_shoff, SEEK_SET) == -1)
+  {
+    perror ("positioning for sections");
+    free(dyns);
+    return 1;
+  }
+
+  for (i = 0; i < ehdr.e_shnum; i++)
+  {
+    if (read(fd, &shdr, sizeof(shdr)) != sizeof(shdr))
+    {
+      perror ("reading section header");
+      free(dyns);
+      return 1;
+    }
+    if (shdr.sh_type == SHT_STRTAB)
+      break;
+  }
+  if (i == ehdr.e_shnum)
+    {
+      fprintf (stderr, "No string table found.\n");
+      free(dyns);
+      return 2;
+    }
+  strtab = (char *)malloc(shdr.sh_size);
+  if (strtab == NULL)
+    {
+      perror ("allocating memory for string table");
+      free(dyns);
+      return 1;
+    }
+  memset(strtab, 0, shdr.sh_size);
+
+  if (lseek(fd, shdr.sh_offset, SEEK_SET) == -1)
+  {
+    perror ("positioning for string table");
+    free(strtab);
+    free(dyns);
+    return 1;
+  }
+  if (read(fd, strtab, shdr.sh_size) != (int)shdr.sh_size)
+  {
+    perror ("reading string table");
+    free(strtab);
+    free(dyns);
+    return 1;
+  }
+
+  if ((int)shdr.sh_size < rpathoff)
+  {
+    fprintf(stderr, "%s string offset not contained in string table",
+            elf_tagname(dyns[rpath_dyns_index].d_tag));
+    free(strtab);
+    free(dyns);
+    return 5;
+  }
+  rpath = strtab+rpathoff;
+
+#if defined(DT_RUNPATH)
+  if (convert && dyns[rpath_dyns_index].d_tag == DT_RPATH)
+  {
+    dyns[rpath_dyns_index].d_tag = DT_RUNPATH;
+    if (lseek(fd, phdr.p_offset, SEEK_SET) == -1
+        || write(fd, dyns, phdr.p_filesz) != (int)phdr.p_filesz)
+    {
+      perror ("converting RPATH to RUNPATH");
+      return 1;
+    }
+    printf("%s: RPATH converted to RUNPATH\n", filename);
+  }
+#endif /* DT_RUNPATH */
+
+  printf("%s: %s=%s\n", filename, elf_tagname(dyns[rpath_dyns_index].d_tag),
+         rpath);
+
+  if (NULL == newpath)
+  {
+    free(dyns);
+    free(strtab);
+    return 0;
+  }
+
+  rpathlen = strlen(rpath);
+
+  /*
+   * Calculate the maximum rpath length (will be equal to rpathlen unless
+   * we have previously truncated it).
+   */
+  for ( i = rpathoff + rpathlen ; (i < (int)shdr.sh_size
+                                   && strtab[i] == '\0') ; i++ )
+    ;
+  i--;
+
+  if (i > (int)(rpathoff + rpathlen))
+     rpathlen = i - rpathoff;
+
+  if (strlen(newpath) > rpathlen)
+  {
+    fprintf(stderr, "new rpath '%s' too large; maximum length %i\n",
+            newpath, rpathlen);
+    free(dyns);
+    free(strtab);
+    return 7;
+  }
+
+  memset(rpath, 0, rpathlen);
+  strcpy(rpath, newpath);
+
+  if (lseek(fd, shdr.sh_offset+rpathoff, SEEK_SET) == -1)
+  {
+    perror ("positioning for RPATH");
+    free(dyns);
+    free(strtab);
+    return 1;
+  }
+  if (write(fd, rpath, rpathlen) != (int)rpathlen)
+  {
+    perror ("writing RPATH");
+    free(dyns);
+    free(strtab);
+    return 1;
+  }
+  printf("%s: new %s: %s\n", filename,
+         elf_tagname(dyns[rpath_dyns_index].d_tag), rpath);
+
+  elf_close(fd);
+
+  free(dyns);
+  dyns = NULL;
+
+  free(strtab);
+
+  return 0;
+}