nonnacl_util/linux/get_plugin_dirname.cc

   1 /*
   2  * Copyright 2008, Google Inc.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met:
   8  *
   9  *     * Redistributions of source code must retain the above copyright
  10  * notice, this list of conditions and the following disclaimer.
  11  *     * Redistributions in binary form must reproduce the above
  12  * copyright notice, this list of conditions and the following disclaimer
  13  * in the documentation and/or other materials provided with the
  14  * distribution.
  15  *     * Neither the name of Google Inc. nor the names of its
  16  * contributors may be used to endorse or promote products derived from
  17  * this software without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  20  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  21  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  22  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  23  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  26  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  27  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  28  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  29  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  30  */
  31
  32
  33 /* TODO: add comment why this is needed */
  34 #ifndef _GNU_SOURCE
  35 #define _GNU_SOURCE
  36 #endif
  37 #include <dlfcn.h>
  38 #include <libgen.h>
  39 #include <linux/limits.h>
  40 #include <signal.h>
  41 #include <stdio.h>
  42 #include <stdint.h>
  43 #include <stdlib.h>
  44 #include <string.h>
  45 #include <sys/types.h>
  46 #include <sys/wait.h>
  47 #include <unistd.h>
  48
  49 #include "native_client/nonnacl_util/sel_ldr_launcher.h"
  50
  51 namespace nacl {
  52
  53
  54 const char* SelLdrLauncher::GetPluginDirname() {
  55   Dl_info     info;
  56   char*       pathname = NULL;
  57   static char bin_dir[2 * PATH_MAX + 1];
  58   // C++ really does not like to convert function pointer to regular pointers.
  59   // This is apparently the only way to do it without compiler warnings
  60   void* sym_addr = reinterpret_cast<void*>(
  61     reinterpret_cast<uintptr_t>(GetPluginDirname));
  62
  63   // First, try looking a symbol up in the dynamic loader's records.
  64   if (0 == dladdr(sym_addr, &info)) {
  65     printf("dladdr failed\n");
  66   } else {
  67     strncpy(bin_dir, info.dli_fname, sizeof(bin_dir));
  68     pathname = bin_dir;
  69   }
  70   // What follows is probably major overkill if the dladdr scheme works.
  71   if (NULL == pathname) {
  72     // Identify the path the plugin was loaded from.  For Linux we look through
  73     // the address ranges in /proc/self/maps for the address of a static
  74     // variable. If that fails, look in /proc/self/exe.
  75     FILE* fp;
  76
  77     // Open the file, returning NULL for failure.
  78     if (NULL == (fp = fopen("/proc/self/maps", "r"))) {
  79       return NULL;
  80     }
  81     // Read line by line.
  82     while (!feof(fp)) {
  83       static int dummy_for_address;
  84       const unsigned kAddressInSo = (unsigned) &dummy_for_address;
  85       uintptr_t low_addr;
  86       uintptr_t high_addr;
  87       char perm[5];
  88       uintptr_t offset;
  89       unsigned dev_maj;
  90       unsigned dev_min;
  91       unsigned inode;
  92
  93       if (7 != fscanf(fp, "%x-%x %s %x %x:%x %x",
  94                       &low_addr, &high_addr, perm, &offset, &dev_maj,
  95                       &dev_min, &inode)) {
  96         return NULL;
  97       }
  98       if (NULL == fgets(bin_dir, sizeof(bin_dir), fp)) {
  99         return NULL;
 100       }
 101       // If the address is in the range, break out of the loop.
 102       if (kAddressInSo >= low_addr && kAddressInSo < high_addr) {
 103         pathname = strchr(bin_dir, '/');
 104         break;
 105       }
 106     }
 107     // Close /proc/self/maps.
 108     fclose(fp);
 109   }
 110   // If we didn't find a matching pathname, try the path of the current
 111   // executable.
 112   if (NULL == pathname) {
 113     int bin_dir_size = readlink("/proc/self/exe", bin_dir, PATH_MAX);
 114     if (bin_dir_size < 0 || bin_dir_size > PATH_MAX) {
 115       return NULL;
 116     }
 117     bin_dir[bin_dir_size] = '\0';
 118     pathname = bin_dir;
 119   }
 120   // Return just the directory path.
 121   return dirname(pathname);
 122 }
 123
 124
 125 }  // namespace nacl