gdb: allow gdbclient.py to find local files.

gdbclient.py is always downloading the stripped version of executable
files from the device. This CL first tries to find the unstripped local
file before falling back to the stripped version.

Bug: http://b/24947939
Change-Id: I7a49d0d8b28590ee99ce892d3e3476921f4ae974

python-packages/gdbrunner/__init__.py

@@ -167,24 +167,65 @@ def start_gdbserver(device, gdbserver_local_path, gdbserver_remote_path,
                               stderr=gdbclient_output)
 
 
-def pull_file(device, path, user=None):
-    """Pull a file from a device as a user."""
+def find_file(device, executable_path, sysroot, user=None):
+    """Finds a device executable file.
 
-    file_name = "gdbclient-binary-{}".format(os.getppid())
-    remote_temp_path = "/data/local/tmp/{}".format(file_name)
-    local_temp_path = os.path.join(tempfile.gettempdir(), file_name)
-    cmd = get_run_as_cmd(user, ["cat", path, ">", remote_temp_path])
-    try:
-        device.shell(cmd)
-    except adb.ShellError:
-        raise RuntimeError("Failed to copy file to temporary folder on device")
-    device.pull(remote_temp_path, local_temp_path)
-    return open(local_temp_path, "r")
+    This function first attempts to find the local file which will
+    contain debug symbols. If that fails, it will fall back to
+    downloading the stripped file from the device.
+
+    Args:
+      device: the AndroidDevice object to use.
+      executable_path: absolute path to the executable or symlink.
+      sysroot: absolute path to the built symbol sysroot.
+      user: if necessary, the user to download the file as.
+
+    Returns:
+      A tuple containing (<open file object>, <was found locally>).
+
+    Raises:
+      RuntimeError: could not find the executable binary.
+      ValueError: |executable_path| is not absolute.
+    """
+    if not os.path.isabs(executable_path):
+        raise ValueError("'{}' is not an absolute path".format(executable_path))
+
+    def generate_files():
+        """Yields (<file name>, <found locally>) tuples."""
+        # First look locally to avoid shelling into the device if possible.
+        # os.path.join() doesn't combine absolute paths, use + instead.
+        yield (sysroot + executable_path, True)
+
+        # Next check if the path is a symlink.
+        try:
+            target = device.shell(['readlink', '-e', '-n', executable_path])[0]
+            yield (sysroot + target, True)
+        except adb.ShellError:
+            pass
+
+        # Last, download the stripped executable from the device if necessary.
+        file_name = "gdbclient-binary-{}".format(os.getppid())
+        remote_temp_path = "/data/local/tmp/{}".format(file_name)
+        local_path = os.path.join(tempfile.gettempdir(), file_name)
+        cmd = get_run_as_cmd(user,
+                             ["cat", executable_path, ">", remote_temp_path])
+        try:
+            device.shell(cmd)
+        except adb.ShellError:
+            raise RuntimeError("Failed to copy '{}' to temporary folder on "
+                               "device".format(executable_path))
+        device.pull(remote_temp_path, local_path)
+        yield (local_path, False)
+
+    for path, found_locally in generate_files():
+        if os.path.isfile(path):
+            return (open(path, "r"), found_locally)
+    raise RuntimeError('Could not find executable {}'.format(executable_path))
 
 
-def pull_binary(device, pid, user=None):
-    """Pull a running process's binary from a device as a user"""
-    return pull_file(device, "/proc/{}/exe".format(pid), user)
+def find_binary(device, pid, sysroot, user=None):
+    """Finds a device executable file corresponding to |pid|."""
+    return find_file(device, "/proc/{}/exe".format(pid), sysroot, user)
 
 
 def get_binary_arch(binary_file):

scripts/gdbclient.py

@@ -106,7 +106,7 @@ def ensure_linker(device, sysroot, is64bit):
         device.pull(remote_path, local_path)
 
 
-def handle_switches(args):
+def handle_switches(args, sysroot):
     """Fetch the targeted binary and determine how to attach gdb.
 
     Args:
@@ -135,14 +135,20 @@ def handle_switches(args):
         if not args.run_cmd[0].startswith("/"):
             sys.exit("commands passed to -r must use absolute paths")
         run_cmd = args.run_cmd
-        binary_file = gdbrunner.pull_file(device, run_cmd[0], user=args.user)
+        binary_file, local = gdbrunner.find_file(device, run_cmd[0], sysroot,
+                                                 user=args.user)
     if binary_file is None:
         assert pid is not None
         try:
-            binary_file = gdbrunner.pull_binary(device, pid=pid, user=args.user)
+            binary_file, local = gdbrunner.find_binary(device, pid, sysroot,
+                                                       user=args.user)
         except adb.ShellError:
             sys.exit("failed to pull binary for PID {}".format(pid))
 
+    if not local:
+        logging.warning("Couldn't find local unstripped executable in {},"
+                        " symbols may not be available.".format(sysroot))
+
     return (binary_file, pid, run_cmd)
 
 def generate_gdb_script(sysroot, binary_file, is64bit, port, connect_timeout=5):
@@ -216,7 +222,7 @@ def main():
     run_cmd = None
 
     # Fetch binary for -p, -n.
-    binary_file, pid, run_cmd = handle_switches(args)
+    binary_file, pid, run_cmd = handle_switches(args, sysroot)
 
     with binary_file:
         arch = gdbrunner.get_binary_arch(binary_file)
@@ -249,6 +255,9 @@ def main():
         gdb_path = os.path.join(root, "prebuilts", "gdb", platform_name, "bin",
                                 "gdb")
 
+        # Print a newline to separate our messages from the GDB session.
+        print("")
+
         # Start gdb.
         gdbrunner.start_gdb(gdb_path, gdb_commands)