tools/android/run_pie/run_pie.c

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include <dlfcn.h>
   6 #include <stdio.h>
   7 #include <string.h>
   8 #include <sys/prctl.h>
   9 #include <unistd.h>
  10
  11 // This is a wrapper to run position independent executables on Android ICS,
  12 // where the linker doesn't support PIE. This requires the PIE binaries to be
  13 // built with CFLAGS +=-fvisibility=default -fPIE, and LDFLAGS += -rdynamic -pie
  14 // such that the main() symbol remains exported and can be dlsym-ed.
  15
  16 #define ERR_PREFIX "[PIE Loader] "
  17
  18 typedef int (*main_t)(int, char**);
  19
  20
  21 int main(int argc, char** argv) {
  22   if (argc < 2) {
  23     printf("Usage: %s path_to_pie_executable [args]\n", argv[0]);
  24     return -1;
  25   }
  26
  27   // Shift left the argv[]. argv is what /proc/PID/cmdline prints out. In turn
  28   // cmdline is what Android "ps" prints out. In turn "ps" is what many scripts
  29   // look for to decide which processes to kill / killall.
  30   int i;
  31   char* next_argv_start = argv[0];
  32   for (i = 1; i < argc; ++i) {
  33     const size_t argv_len = strlen(argv[i]) + 1;
  34     memcpy(argv[i - 1], argv[i], argv_len);
  35     next_argv_start += argv_len;
  36     argv[i] = next_argv_start;
  37   }
  38   argv[argc - 1] = NULL;  // The last argv must be a NULL ptr.
  39
  40   // Set also the proc name accordingly (/proc/PID/comm).
  41   prctl(PR_SET_NAME, (long) argv[0]);
  42
  43   // dlopen should not fail, unless:
  44   // - The target binary does not exists:
  45   // - The dependent .so libs cannot be loaded.
  46   // In both cases, just bail out with an explicit error message.
  47   void* handle = dlopen(argv[0], RTLD_NOW);
  48   if (handle == NULL) {
  49     printf(ERR_PREFIX "dlopen() failed: %s.\n", dlerror());
  50     return -1;
  51   }
  52
  53   main_t pie_main = (main_t) dlsym(handle, "main");
  54   if (pie_main) {
  55     return pie_main(argc - 1, argv);
  56   }
  57
  58   // If we reached this point dlsym failed, very likely because the target
  59   // binary has not been compiled with the proper CFLAGS / LDFLAGS.
  60   // At this point the most sensible thing to do is running that normally
  61   // via exec and hope that the target binary wasn't a PIE.
  62   execv(argv[0], argv);
  63
  64   // exevc is supposed to never return, unless it fails.
  65   printf(ERR_PREFIX "Both dlsym() and the execv() fallback failed.\n");
  66   perror("execv");
  67   return -1;
  68 }