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binreloc.c

/*
 * BinReloc - a library for creating relocatable executables
 * Written by: Hongli Lai <h.lai@chello.nl>
 * http://autopackage.org/
 *
 * This source code is public domain. You can relicense this code
 * under whatever license you want.
 *
 * See http://autopackage.org/docs/binreloc/ for
 * more information and how to use this.
 */

#ifndef __BINRELOC_C__
#define __BINRELOC_C__

#ifdef ENABLE_BINRELOC
      #include <sys/types.h>
      #include <sys/stat.h>
      #include <unistd.h>
#endif /* ENABLE_BINRELOC */
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <string.h>
#include "binreloc.h"

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */



/** @internal
 * Find the canonical filename of the executable. Returns the filename
 * (which must be freed) or NULL on error. If the parameter 'error' is
 * not NULL, the error code will be stored there, if an error occured.
 */
static char *
_br_find_exe (BrInitError *error)
{
#ifndef ENABLE_BINRELOC
      if (error)
            *error = BR_INIT_ERROR_DISABLED;
      return NULL;
#else
      char *path, *path2, *line, *result;
      size_t buf_size;
      ssize_t size;
      struct stat stat_buf;
      FILE *f;

      /* Read from /proc/self/exe (symlink) */
      if (sizeof (path) > SSIZE_MAX)
            buf_size = SSIZE_MAX - 1;
      else
            buf_size = PATH_MAX - 1;
      path = (char *) malloc (buf_size);
      if (path == NULL) {
            /* Cannot allocate memory. */
            if (error)
                  *error = BR_INIT_ERROR_NOMEM;
            return NULL;
      }
      path2 = (char *) malloc (buf_size);
      if (path2 == NULL) {
            /* Cannot allocate memory. */
            if (error)
                  *error = BR_INIT_ERROR_NOMEM;
            free (path);
            return NULL;
      }

      strncpy (path2, "/proc/self/exe", buf_size - 1);

      while (1) {
            int i;

            size = readlink (path2, path, buf_size - 1);
            if (size == -1) {
                  /* Error. */
                  free (path2);
                  break;
            }

            /* readlink() success. */
            path[size] = '\0';

            /* Check whether the symlink's target is also a symlink.
             * We want to get the final target. */
            i = stat (path, &stat_buf);
            if (i == -1) {
                  /* Error. */
                  free (path2);
                  break;
            }

            /* stat() success. */
            if (!S_ISLNK (stat_buf.st_mode)) {
                  /* path is not a symlink. Done. */
                  free (path2);
                  return path;
            }

            /* path is a symlink. Continue loop and resolve this. */
            strncpy (path, path2, buf_size - 1);
      }


      /* readlink() or stat() failed; this can happen when the program is
       * running in Valgrind 2.2. Read from /proc/self/maps as fallback. */

      buf_size = PATH_MAX + 128;
      line = (char *) realloc (path, buf_size);
      if (line == NULL) {
            /* Cannot allocate memory. */
            free (path);
            if (error)
                  *error = BR_INIT_ERROR_NOMEM;
            return NULL;
      }

      f = fopen ("/proc/self/maps", "r");
      if (f == NULL) {
            free (line);
            if (error)
                  *error = BR_INIT_ERROR_OPEN_MAPS;
            return NULL;
      }

      /* The first entry should be the executable name. */
      result = fgets (line, (int) buf_size, f);
      if (result == NULL) {
            fclose (f);
            free (line);
            if (error)
                  *error = BR_INIT_ERROR_READ_MAPS;
            return NULL;
      }

      /* Get rid of newline character. */
      buf_size = strlen (line);
      if (buf_size <= 0) {
            /* Huh? An empty string? */
            fclose (f);
            free (line);
            if (error)
                  *error = BR_INIT_ERROR_INVALID_MAPS;
            return NULL;
      }
      if (line[buf_size - 1] == 10)
            line[buf_size - 1] = 0;

      /* Extract the filename; it is always an absolute path. */
      path = strchr (line, '/');

      /* Sanity check. */
      if (strstr (line, " r-xp ") == NULL || path == NULL) {
            fclose (f);
            free (line);
            if (error)
                  *error = BR_INIT_ERROR_INVALID_MAPS;
            return NULL;
      }

      path = strdup (path);
      free (line);
      fclose (f);
      return path;
#endif /* ENABLE_BINRELOC */
}


/** @internal
 * Find the canonical filename of the executable which owns symbol.
 * Returns a filename which must be freed, or NULL on error.
 */
static char *
_br_find_exe_for_symbol (const void *symbol, BrInitError *error)
{
#ifndef ENABLE_BINRELOC
      if (error)
            *error = BR_INIT_ERROR_DISABLED;
      return (char *) NULL;
#else
      #define SIZE PATH_MAX + 100
      FILE *f;
      size_t address_string_len;
      char *address_string, line[SIZE], *found;

      if (symbol == NULL)
            return (char *) NULL;

      f = fopen ("/proc/self/maps", "r");
      if (f == NULL)
            return (char *) NULL;

      address_string_len = 4;
      address_string = (char *) malloc (address_string_len);
      found = (char *) NULL;

      while (!feof (f)) {
            char *start_addr, *end_addr, *end_addr_end, *file;
            void *start_addr_p, *end_addr_p;
            size_t len;

            if (fgets (line, SIZE, f) == NULL)
                  break;

            /* Sanity check. */
            if (strstr (line, " r-xp ") == NULL || strchr (line, '/') == NULL)
                  continue;

            /* Parse line. */
            start_addr = line;
            end_addr = strchr (line, '-');
            file = strchr (line, '/');

            /* More sanity check. */
            if (!(file > end_addr && end_addr != NULL && end_addr[0] == '-'))
                  continue;

            end_addr[0] = '\0';
            end_addr++;
            end_addr_end = strchr (end_addr, ' ');
            if (end_addr_end == NULL)
                  continue;

            end_addr_end[0] = '\0';
            len = strlen (file);
            if (len == 0)
                  continue;
            if (file[len - 1] == '\n')
                  file[len - 1] = '\0';

            /* Get rid of "(deleted)" from the filename. */
            len = strlen (file);
            if (len > 10 && strcmp (file + len - 10, " (deleted)") == 0)
                  file[len - 10] = '\0';

            /* I don't know whether this can happen but better safe than sorry. */
            len = strlen (start_addr);
            if (len != strlen (end_addr))
                  continue;


            /* Transform the addresses into a string in the form of 0xdeadbeef,
             * then transform that into a pointer. */
            if (address_string_len < len + 3) {
                  address_string_len = len + 3;
                  address_string = (char *) realloc (address_string, address_string_len);
            }

            memcpy (address_string, "0x", 2);
            memcpy (address_string + 2, start_addr, len);
            address_string[2 + len] = '\0';
            sscanf (address_string, "%p", &start_addr_p);

            memcpy (address_string, "0x", 2);
            memcpy (address_string + 2, end_addr, len);
            address_string[2 + len] = '\0';
            sscanf (address_string, "%p", &end_addr_p);


            if (symbol >= start_addr_p && symbol < end_addr_p) {
                  found = file;
                  break;
            }
      }

      free (address_string);
      fclose (f);

      if (found == NULL)
            return (char *) NULL;
      else
            return strdup (found);
#endif /* ENABLE_BINRELOC */
}


#ifndef BINRELOC_RUNNING_DOXYGEN
      #undef NULL
      #define NULL ((void *) 0) /* typecasted as char* for C++ type safeness */
#endif

static char *exe = (char *) NULL;


/** Initialize the BinReloc library (for applications).
 *
 * This function must be called before using any other BinReloc functions.
 * It attempts to locate the application's canonical filename.
 *
 * @note If you want to use BinReloc for a library, then you should call
 *       br_init_lib() instead.
 *
 * @param error  If BinReloc failed to initialize, then the error code will
 *               be stored in this variable. Set to NULL if you want to
 *               ignore this. See #BrInitError for a list of error codes.
 *
 * @returns 1 on success, 0 if BinReloc failed to initialize.
 */
int
br_init (BrInitError *error)
{
      exe = _br_find_exe (error);
      return exe != NULL;
}


/** Initialize the BinReloc library (for libraries).
 *
 * This function must be called before using any other BinReloc functions.
 * It attempts to locate the calling library's canonical filename.
 *
 * @note The BinReloc source code MUST be included in your library, or this
 *       function won't work correctly.
 *
 * @param error  If BinReloc failed to initialize, then the error code will
 *               be stored in this variable. Set to NULL if you want to
 *               ignore this. See #BrInitError for a list of error codes.
 *
 * @returns 1 on success, 0 if a filename cannot be found.
 */
int
br_init_lib (BrInitError *error)
{
      exe = _br_find_exe_for_symbol ((const void *) "", error);
      return exe != NULL;
}


/** Find the canonical filename of the current application.
 *
 * @param default_exe  A default filename which will be used as fallback.
 * @returns A string containing the application's canonical filename,
 *          which must be freed when no longer necessary. If BinReloc is
 *          not initialized, or if br_init() failed, then a copy of
 *          default_exe will be returned. If default_exe is NULL, then
 *          NULL will be returned.
 */
char *
br_find_exe (const char *default_exe)
{
      if (exe == (char *) NULL) {
            /* BinReloc is not initialized. */
            if (default_exe != (const char *) NULL)
                  return strdup (default_exe);
            else
                  return (char *) NULL;
      }
      return strdup (exe);
}


/** Locate the directory in which the current application is installed.
 *
 * The prefix is generated by the following pseudo-code evaluation:
 * \code
 * dirname(exename)
 * \endcode
 *
 * @param default_dir  A default directory which will used as fallback.
 * @return A string containing the directory, which must be freed when no
 *         longer necessary. If BinReloc is not initialized, or if the
 *         initialization function failed, then a copy of default_dir
 *         will be returned. If default_dir is NULL, then NULL will be
 *         returned.
 */
char *
br_find_exe_dir (const char *default_dir)
{
      if (exe == NULL) {
            /* BinReloc not initialized. */
            if (default_dir != NULL)
                  return strdup (default_dir);
            else
                  return NULL;
      }

      return br_dirname (exe);
}


/** Locate the prefix in which the current application is installed.
 *
 * The prefix is generated by the following pseudo-code evaluation:
 * \code
 * dirname(dirname(exename))
 * \endcode
 *
 * @param default_prefix  A default prefix which will used as fallback.
 * @return A string containing the prefix, which must be freed when no
 *         longer necessary. If BinReloc is not initialized, or if
 *         the initialization function failed, then a copy of default_prefix
 *         will be returned. If default_prefix is NULL, then NULL will be returned.
 */
char *
br_find_prefix (const char *default_prefix)
{
      char *dir1, *dir2;

      if (exe == (char *) NULL) {
            /* BinReloc not initialized. */
            if (default_prefix != (const char *) NULL)
                  return strdup (default_prefix);
            else
                  return (char *) NULL;
      }

      dir1 = br_dirname (exe);
      dir2 = br_dirname (dir1);
      free (dir1);
      return dir2;
}


/** Locate the application's binary folder.
 *
 * The path is generated by the following pseudo-code evaluation:
 * \code
 * prefix + "/bin"
 * \endcode
 *
 * @param default_bin_dir  A default path which will used as fallback.
 * @return A string containing the bin folder's path, which must be freed when
 *         no longer necessary. If BinReloc is not initialized, or if
 *         the initialization function failed, then a copy of default_bin_dir will
 *         be returned. If default_bin_dir is NULL, then NULL will be returned.
 */
char *
br_find_bin_dir (const char *default_bin_dir)
{
      char *prefix, *dir;

      prefix = br_find_prefix ((const char *) NULL);
      if (prefix == (char *) NULL) {
            /* BinReloc not initialized. */
            if (default_bin_dir != (const char *) NULL)
                  return strdup (default_bin_dir);
            else
                  return (char *) NULL;
      }

      dir = br_build_path (prefix, "bin");
      free (prefix);
      return dir;
}


/** Locate the application's superuser binary folder.
 *
 * The path is generated by the following pseudo-code evaluation:
 * \code
 * prefix + "/sbin"
 * \endcode
 *
 * @param default_sbin_dir  A default path which will used as fallback.
 * @return A string containing the sbin folder's path, which must be freed when
 *         no longer necessary. If BinReloc is not initialized, or if the
 *         initialization function failed, then a copy of default_sbin_dir will
 *         be returned. If default_bin_dir is NULL, then NULL will be returned.
 */
char *
br_find_sbin_dir (const char *default_sbin_dir)
{
      char *prefix, *dir;

      prefix = br_find_prefix ((const char *) NULL);
      if (prefix == (char *) NULL) {
            /* BinReloc not initialized. */
            if (default_sbin_dir != (const char *) NULL)
                  return strdup (default_sbin_dir);
            else
                  return (char *) NULL;
      }

      dir = br_build_path (prefix, "sbin");
      free (prefix);
      return dir;
}


/** Locate the application's data folder.
 *
 * The path is generated by the following pseudo-code evaluation:
 * \code
 * prefix + "/share"
 * \endcode
 *
 * @param default_data_dir  A default path which will used as fallback.
 * @return A string containing the data folder's path, which must be freed when
 *         no longer necessary. If BinReloc is not initialized, or if the
 *         initialization function failed, then a copy of default_data_dir
 *         will be returned. If default_data_dir is NULL, then NULL will be
 *         returned.
 */
char *
br_find_data_dir (const char *default_data_dir)
{
      char *prefix, *dir;

      prefix = br_find_prefix ((const char *) NULL);
      if (prefix == (char *) NULL) {
            /* BinReloc not initialized. */
            if (default_data_dir != (const char *) NULL)
                  return strdup (default_data_dir);
            else
                  return (char *) NULL;
      }

      dir = br_build_path (prefix, "share");
      free (prefix);
      return dir;
}


/** Locate the application's localization folder.
 *
 * The path is generated by the following pseudo-code evaluation:
 * \code
 * prefix + "/share/locale"
 * \endcode
 *
 * @param default_locale_dir  A default path which will used as fallback.
 * @return A string containing the localization folder's path, which must be freed when
 *         no longer necessary. If BinReloc is not initialized, or if the
 *         initialization function failed, then a copy of default_locale_dir will be returned.
 *         If default_locale_dir is NULL, then NULL will be returned.
 */
char *
br_find_locale_dir (const char *default_locale_dir)
{
      char *data_dir, *dir;

      data_dir = br_find_data_dir ((const char *) NULL);
      if (data_dir == (char *) NULL) {
            /* BinReloc not initialized. */
            if (default_locale_dir != (const char *) NULL)
                  return strdup (default_locale_dir);
            else
                  return (char *) NULL;
      }

      dir = br_build_path (data_dir, "locale");
      free (data_dir);
      return dir;
}


/** Locate the application's library folder.
 *
 * The path is generated by the following pseudo-code evaluation:
 * \code
 * prefix + "/lib"
 * \endcode
 *
 * @param default_lib_dir  A default path which will used as fallback.
 * @return A string containing the library folder's path, which must be freed when
 *         no longer necessary. If BinReloc is not initialized, or if the initialization
 *         function failed, then a copy of default_lib_dir will be returned.
 *         If default_lib_dir is NULL, then NULL will be returned.
 */
char *
br_find_lib_dir (const char *default_lib_dir)
{
      char *prefix, *dir;

      prefix = br_find_prefix ((const char *) NULL);
      if (prefix == (char *) NULL) {
            /* BinReloc not initialized. */
            if (default_lib_dir != (const char *) NULL)
                  return strdup (default_lib_dir);
            else
                  return (char *) NULL;
      }

      dir = br_build_path (prefix, "lib");
      free (prefix);
      return dir;
}


/** Locate the application's libexec folder.
 *
 * The path is generated by the following pseudo-code evaluation:
 * \code
 * prefix + "/libexec"
 * \endcode
 *
 * @param default_libexec_dir  A default path which will used as fallback.
 * @return A string containing the libexec folder's path, which must be freed when
 *         no longer necessary. If BinReloc is not initialized, or if the initialization
 *         function failed, then a copy of default_libexec_dir will be returned.
 *         If default_libexec_dir is NULL, then NULL will be returned.
 */
char *
br_find_libexec_dir (const char *default_libexec_dir)
{
      char *prefix, *dir;

      prefix = br_find_prefix ((const char *) NULL);
      if (prefix == (char *) NULL) {
            /* BinReloc not initialized. */
            if (default_libexec_dir != (const char *) NULL)
                  return strdup (default_libexec_dir);
            else
                  return (char *) NULL;
      }

      dir = br_build_path (prefix, "libexec");
      free (prefix);
      return dir;
}


/** Locate the application's configuration files folder.
 *
 * The path is generated by the following pseudo-code evaluation:
 * \code
 * prefix + "/etc"
 * \endcode
 *
 * @param default_etc_dir  A default path which will used as fallback.
 * @return A string containing the etc folder's path, which must be freed when
 *         no longer necessary. If BinReloc is not initialized, or if the initialization
 *         function failed, then a copy of default_etc_dir will be returned.
 *         If default_etc_dir is NULL, then NULL will be returned.
 */
char *
br_find_etc_dir (const char *default_etc_dir)
{
      char *prefix, *dir;

      prefix = br_find_prefix ((const char *) NULL);
      if (prefix == (char *) NULL) {
            /* BinReloc not initialized. */
            if (default_etc_dir != (const char *) NULL)
                  return strdup (default_etc_dir);
            else
                  return (char *) NULL;
      }

      dir = br_build_path (prefix, "etc");
      free (prefix);
      return dir;
}


/***********************
 * Utility functions
 ***********************/

/** Concatenate str1 and str2 to a newly allocated string.
 *
 * @param str1 A string.
 * @param str2 Another string.
 * @returns A newly-allocated string. This string should be freed when no longer needed.
 */
char *
br_strcat (const char *str1, const char *str2)
{
      char *result;
      size_t len1, len2;

      if (str1 == NULL)
            str1 = "";
      if (str2 == NULL)
            str2 = "";

      len1 = strlen (str1);
      len2 = strlen (str2);

      result = (char *) malloc (len1 + len2 + 1);
      memcpy (result, str1, len1);
      memcpy (result + len1, str2, len2);
      result[len1 + len2] = '\0';

      return result;
}


char *
br_build_path (const char *dir, const char *file)
{
      char *dir2, *result;
      size_t len;
      int must_free = 0;

      len = strlen (dir);
      if (len > 0 && dir[len - 1] != '/') {
            dir2 = br_strcat (dir, "/");
            must_free = 1;
      } else
            dir2 = (char *) dir;

      result = br_strcat (dir2, file);
      if (must_free)
            free (dir2);
      return result;
}


/* Emulates glibc's strndup() */
static char *
br_strndup (const char *str, size_t size)
{
      char *result = (char *) NULL;
      size_t len;

      if (str == (const char *) NULL)
            return (char *) NULL;

      len = strlen (str);
      if (len == 0)
            return strdup ("");
      if (size > len)
            size = len;

      result = (char *) malloc (len + 1);
      memcpy (result, str, size);
      result[size] = '\0';
      return result;
}


/** Extracts the directory component of a path.
 *
 * Similar to g_dirname() or the dirname commandline application.
 *
 * Example:
 * \code
 * br_dirname ("/usr/local/foobar");  --> Returns: "/usr/local"
 * \endcode
 *
 * @param path  A path.
 * @returns     A directory name. This string should be freed when no longer needed.
 */
char *
br_dirname (const char *path)
{
      char *end, *result;

      if (path == (const char *) NULL)
            return (char *) NULL;

      end = strrchr (path, '/');
      if (end == (const char *) NULL)
            return strdup (".");

      while (end > path && *end == '/')
            end--;
      result = br_strndup (path, end - path + 1);
      if (result[0] == 0) {
            free (result);
            return strdup ("/");
      } else
            return result;
}


#ifdef __cplusplus
}
#endif /* __cplusplus */

#endif /* __BINRELOC_C__ */

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