File: gimpreloc.c

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/*
 * 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.
 */

#include "config.h"

#include <stdlib.h>
#include <limits.h>
#include <string.h>

#ifdef ENABLE_BINRELOC
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#endif /* ENABLE_BINRELOC */

#include <glib.h>
#include <glib/gstdio.h>

#include "gimpreloc.h"

#ifndef PATH_MAX
#define PATH_MAX 4096
#endif

/*
 * 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 occurred.
 */
static char *
_br_find_exe (GimpBinrelocInitError *error)
{
#ifndef ENABLE_BINRELOC
        if (error)
                *error = GIMP_RELOC_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 = g_try_new (char, buf_size);
        if (path == NULL) {
                /* Cannot allocate memory. */
                if (error)
                        *error = GIMP_RELOC_INIT_ERROR_NOMEM;
                return NULL;
        }
        path2 = g_try_new (char, buf_size);
        if (path2 == NULL) {
                /* Cannot allocate memory. */
                if (error)
                        *error = GIMP_RELOC_INIT_ERROR_NOMEM;
                g_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. */
                        g_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. */
                        g_free (path2);
                        break;
                }

                /* stat() success. */
                if (!S_ISLNK (stat_buf.st_mode)) {
                        /* path is not a symlink. Done. */
                        g_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 *) g_try_realloc (path, buf_size);
        if (line == NULL) {
                /* Cannot allocate memory. */
                g_free (path);
                if (error)
                        *error = GIMP_RELOC_INIT_ERROR_NOMEM;
                return NULL;
        }

        f = g_fopen ("/proc/self/maps", "r");
        if (f == NULL) {
                g_free (line);
                if (error)
                        *error = GIMP_RELOC_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);
                g_free (line);
                if (error)
                        *error = GIMP_RELOC_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);
                g_free (line);
                if (error)
                        *error = GIMP_RELOC_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);
                g_free (line);
                if (error)
                        *error = GIMP_RELOC_INIT_ERROR_INVALID_MAPS;
                return NULL;
        }

        path = g_strdup (path);
        g_free (line);
        fclose (f);
        return path;
#endif /* ENABLE_BINRELOC */
}


/*
 * 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, GimpBinrelocInitError *error)
{
#ifndef ENABLE_BINRELOC
        if (error)
                *error = GIMP_RELOC_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 = g_fopen ("/proc/self/maps", "r");
        if (f == NULL)
                return (char *) NULL;

        address_string_len = 4;
        address_string = g_try_new (char, 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 *) g_try_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;
                }
        }

        g_free (address_string);
        fclose (f);

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


static gchar *exe = NULL;

static void set_gerror (GError **error, GimpBinrelocInitError errcode);


/* 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
 *       _gimp_reloc_init_lib() instead.
 * @note Initialization failure is not fatal. BinReloc functions will just
 *       fallback to the supplied default path.
 *
 * @param error  If BinReloc failed to initialize, then the error report will
 *               be stored in this variable. Set to NULL if you don't want an
 *               error report. See the #GimpBinrelocInitError for a list of error
 *               codes.
 *
 * @returns TRUE on success, FALSE if BinReloc failed to initialize.
 */
gboolean
_gimp_reloc_init (GError **error)
{
        GimpBinrelocInitError errcode;

        /* Shut up compiler warning about uninitialized variable. */
        errcode = GIMP_RELOC_INIT_ERROR_NOMEM;

        /* Locate the application's filename. */
        exe = _br_find_exe (&errcode);
        if (exe != NULL)
                /* Success! */
                return TRUE;
        else {
                /* Failed :-( */
                set_gerror (error, errcode);
                return FALSE;
        }
}


/* 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.
 * @note Initialization failure is not fatal. BinReloc functions will just
 *       fallback to the supplied default path.
 *
 * @returns TRUE on success, FALSE if a filename cannot be found.
 */
gboolean
_gimp_reloc_init_lib (GError **error)
{
        GimpBinrelocInitError errcode;

        /* Shut up compiler warning about uninitialized variable. */
        errcode = GIMP_RELOC_INIT_ERROR_NOMEM;

        exe = _br_find_exe_for_symbol ((const void *) "", &errcode);
        if (exe != NULL)
                /* Success! */
                return TRUE;
        else {
                /* Failed :-( */
                set_gerror (error, errcode);
                return exe != NULL;
        }
}

static void
set_gerror (GError **error, GimpBinrelocInitError errcode)
{
        const gchar *error_message;

        if (error == NULL)
                return;

        switch (errcode) {
        case GIMP_RELOC_INIT_ERROR_NOMEM:
                error_message = "Cannot allocate memory.";
                break;
        case GIMP_RELOC_INIT_ERROR_OPEN_MAPS:
                error_message = "Unable to open /proc/self/maps for reading.";
                break;
        case GIMP_RELOC_INIT_ERROR_READ_MAPS:
                error_message = "Unable to read from /proc/self/maps.";
                break;
        case GIMP_RELOC_INIT_ERROR_INVALID_MAPS:
                error_message = "The file format of /proc/self/maps is invalid.";
                break;
        case GIMP_RELOC_INIT_ERROR_DISABLED:
                error_message = "Binary relocation support is disabled.";
                break;
        default:
                error_message = "Unknown error.";
                break;
        };
        g_set_error (error, g_quark_from_static_string ("GBinReloc"),
                     errcode, "%s", error_message);
}


/* 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.
 */
gchar *
_gimp_reloc_find_prefix (const gchar *default_prefix)
{
        gchar *dir1, *dir2;

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

        dir1 = g_path_get_dirname (exe);
        dir2 = g_path_get_dirname (dir1);
        g_free (dir1);
        return dir2;
}