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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 } | |
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