[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.
+
+#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;
+}