| // Copyright 2014 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include <dlfcn.h> |
| #include <stdio.h> |
| #include <string.h> |
| #include <sys/prctl.h> |
| #include <unistd.h> |
| |
| // This is a wrapper to run position independent executables on Android ICS, |
| // where the linker doesn't support PIE. This requires the PIE binaries to be |
| // built with CFLAGS +=-fvisibility=default -fPIE, and LDFLAGS += -rdynamic -pie |
| // such that the main() symbol remains exported and can be dlsym-ed. |
| |
| #define ERR_PREFIX "[PIE Loader] " |
| |
| typedef int (*main_t)(int, char**); |
| |
| |
| int main(int argc, char** argv) { |
| if (argc < 2) { |
| printf("Usage: %s path_to_pie_executable [args]\n", argv[0]); |
| return -1; |
| } |
| |
| // Shift left the argv[]. argv is what /proc/PID/cmdline prints out. In turn |
| // cmdline is what Android "ps" prints out. In turn "ps" is what many scripts |
| // look for to decide which processes to kill / killall. |
| int i; |
| char* next_argv_start = argv[0]; |
| for (i = 1; i < argc; ++i) { |
| const size_t argv_len = strlen(argv[i]) + 1; |
| memcpy(argv[i - 1], argv[i], argv_len); |
| next_argv_start += argv_len; |
| argv[i] = next_argv_start; |
| } |
| argv[argc - 1] = NULL; // The last argv must be a NULL ptr. |
| |
| // Set also the proc name accordingly (/proc/PID/comm). |
| prctl(PR_SET_NAME, (long) argv[0]); |
| |
| // dlopen should not fail, unless: |
| // - The target binary does not exists: |
| // - The dependent .so libs cannot be loaded. |
| // In both cases, just bail out with an explicit error message. |
| void* handle = dlopen(argv[0], RTLD_NOW); |
| if (handle == NULL) { |
| printf(ERR_PREFIX "dlopen() failed: %s.\n", dlerror()); |
| return -1; |
| } |
| |
| main_t pie_main = (main_t) dlsym(handle, "main"); |
| if (pie_main) { |
| return pie_main(argc - 1, argv); |
| } |
| |
| // If we reached this point dlsym failed, very likely because the target |
| // binary has not been compiled with the proper CFLAGS / LDFLAGS. |
| // At this point the most sensible thing to do is running that normally |
| // via exec and hope that the target binary wasn't a PIE. |
| execv(argv[0], argv); |
| |
| // exevc is supposed to never return, unless it fails. |
| printf(ERR_PREFIX "Both dlsym() and the execv() fallback failed.\n"); |
| perror("execv"); |
| return -1; |
| } |