GDB: add --gdb-prerun-commands option to GDB plugin

This feature allows custom GDB commands to be executed before the
actual binary is run. What it can do then, is only limited by the
user's goals.

This is intended to allow complex applications, such as QEMU,
to be debugged inside Avocado tests. Configuring GDB for QEMU,
for example, involves passing signals to the application that
would otherwise result in an event that would stop the debugger.

Signed-off-by: Cleber Rosa <[email protected]>

avocado/plugins/gdb.py

@@ -37,6 +37,14 @@ def configure(self, parser):
                                    'be "<binary>[:breakpoint]". Breakpoint '
                                    'defaults to "main"'))
 
+        gdb_grp.add_argument('--gdb-prerun-commands', action='append',
+                             default=[], metavar='BINARY_PATH:COMMANDS_PATH',
+                             help=('After loading a binary in binary in GDB, '
+                                   'but before actually running it, execute '
+                                   'the given GDB commands in the given file.'
+                                   'BINARY_PATH is optional and if ommited '
+                                   'will apply to all binaries'))
+
         gdb_grp.add_argument('--gdb-enable-core', action='store_true',
                              default=False,
                              help=('Automatically generate a core dump when the'
@@ -49,6 +57,12 @@ def activate(self, app_args):
         try:
             for binary in app_args.gdb_run_bin:
                 runtime.GDB_RUN_BINARY_NAMES_EXPR.append(binary)
+            for commands in app_args.gdb_prerun_commands:
+                if ':' in commands:
+                    binary, commands_path = commands.split(':', 1)
+                    runtime.GDB_PRERUN_COMMANDS['binary'] = commands_path
+                else:
+                    runtime.GDB_PRERUN_COMMANDS[''] = commands
             if app_args.gdb_enable_core:
                 runtime.GDB_ENABLE_CORE = True
         except AttributeError:

avocado/runtime.py

@@ -21,6 +21,10 @@
 #: using the given expression
 GDB_RUN_BINARY_NAMES_EXPR = []
 
+#: After loading a binary in binary in GDB, but before actually running it,
+#: execute the given GDB commands present in the given file, one per line
+GDB_PRERUN_COMMANDS = {}
+
 #: Wether to enable the automatic generation of core dumps for applications
 #: that are run inside the GNU debugger
 GDB_ENABLE_CORE = False

avocado/utils/process.py

@@ -746,10 +746,27 @@ def wait_for_exit(self):
 
         return result
 
+    def _run_pre_commands(self):
+        '''
+        Run commands if user passed a commands file with --gdb-prerun-commands
+        '''
+        binary_name = os.path.basename(self.binary)
+        # The commands file can be specific to a given binary or universal,
+        # start checking for specific ones first
+        prerun_commands_path = runtime.GDB_PRERUN_COMMANDS.get(
+            binary_name,
+            runtime.GDB_PRERUN_COMMANDS.get('', None))
+
+        if prerun_commands_path is not None:
+            prerun_commands = open(prerun_commands_path).readlines()
+            for command in prerun_commands:
+                self.gdb.cmd(command)
+
     def run(self, timeout=None):
         for b in self._get_breakpoints():
             self.gdb.set_break(b, ignore_error=True)
 
+        self._run_pre_commands()
         result = self.gdb.run(self.args[1:])
 
         # Collect gdbserver stdout and stderr file information for debugging

examples/gdb-prerun-scripts/README

@@ -0,0 +1,3 @@
+This directory contains examples of GDB "prerun" command files. These are
+intended to be examples of how to use the "--gdb-prerun-commands" option
+of the Avocado GDB plugin.

examples/gdb-prerun-scripts/pass-sigusr1

@@ -0,0 +1,2 @@
+signal SIGUSR1 pass
+signal SIGUSR1 nostop

man/avocado.rst

@@ -286,6 +286,20 @@ while you are debugging it, avocado has no way to know about its status.
 Avocado will automatically send a `continue` command to the debugger
 when you disconnect from and exit gdb.
 
+If you're debugging a special application and need to setup GDB in custom
+ways by running GDB commands, you can do that with the `--gdb-prerun-commands`
+option::
+
+ $ avocado run --gdb-run-bin=foo:bar --gdb-prerun-commands=/tmp/disable-signals footest
+
+In this example, `/tmp/disable-signals` is a simple text file containing two lines::
+
+ signal SIGUSR1 pass
+ signal SIGUSR1 nostop
+
+Each line is a GDB command, so you can have from simple to very complex
+debuggin environments configured like that.
+
 RECORDING TEST REFERENCE OUTPUT
 ===============================
 

selftests/all/functional/avocado/gdb_tests.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+#
+# See LICENSE for more details.
+#
+# Copyright: Red Hat Inc. 2014
+# Author: Cleber Rosa <[email protected]>
+
+import os
+import sys
+import unittest
+
+# simple magic for using scripts within a source tree
+basedir = os.path.join(os.path.dirname(os.path.abspath(__file__)), '..', '..', '..', '..')
+basedir = os.path.abspath(basedir)
+if os.path.isdir(os.path.join(basedir, 'avocado')):
+    sys.path.append(basedir)
+
+from avocado import runtime
+from avocado.utils import process
+
+
+class GDBPluginTest(unittest.TestCase):
+
+    def test_gdb_prerun_commands(self):
+        os.chdir(basedir)
+        cmd_line = './scripts/avocado run --gdb-prerun-commands=/dev/null sleeptest'
+        process.run(cmd_line)
+
+    def test_gdb_multiple_prerun_commands(self):
+        os.chdir(basedir)
+        cmd_line = ('./scripts/avocado run --gdb-prerun-commands=/dev/null '
+                    '--gdb-prerun-commands=foo:/dev/null sleeptest')
+        process.run(cmd_line)
+
+if __name__ == '__main__':
+    unittest.main()