[Android] Build android tools as PIE and add a wrapper for ICS

tools/android/run_pie/run_pie.c

+/*
+ * 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.
+ */

[bulach, 2014/05/14 12:57:05]

nit: I think we use // instead of multiline comment?
ditto for all comments below.

[Primiano Tucci (use gerrit), 2014/05/14 13:21:23]

OMG, you're asking me to be non ANSI-C compliant? :P
(Ok just because these days not even string.h is ANSI compliant anymore :D)
Done.

+
+#include <dlfcn.h>
+#include <stdio.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)

[bulach, 2014/05/14 12:57:05]

nit: { on this line

[Primiano Tucci (use gerrit), 2014/05/14 13:21:23]

Done.

+{
+  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);

[bulach, 2014/05/14 12:57:05]

nit: s/i-1/i - 1/

[Primiano Tucci (use gerrit), 2014/05/14 13:21:23]

Done.

+    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;
+}