GDB: use gdbserver --server-sdtderr option if available

A new command line option is being added to upstream GDB. This new
option allows gdbserver's own stderr (but not its inferior process
stderr) to be redirected to another file.

If that feature is available on the about to be used gdbserver, then
let's make use of it. This redirects its stderr to /dev/null, because
avocado itself has no real use for gdbserver's own stderr output.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

avocado/gdb.py

@@ -20,6 +20,7 @@ import os
 import time
 import fcntl
 import tempfile
+import commands
 import subprocess
 
 from avocado.utils import network
@@ -457,6 +458,17 @@ class GDBServer(object):
         args = [self.path]
         args += self.REQUIRED_ARGS
 
+        # The output on stderr generated by gdbserver itself is of no use to
+        # avocado. Quite on the contrary, it gets mixed with the "inferior"
+        # process stderr. Support is being added to gdbserver to send its own
+        # stderr output somewhere else. If available, use it.
+        output = commands.getoutput("%s --help" % self.path)
+        if '--server-stderr=' in output:
+            self.redirected_stderr = True
+            args.append('--server-stderr=/dev/null')
+        else:
+            self.redirected_stderr = False
+
         if port is None:
             self.port = network.find_free_port(*self.PORT_RANGE)
         else:

examples/tests/gdbtest.py

@@ -4,6 +4,7 @@ import os
 
 from avocado import test
 from avocado import gdb
+from avocado import runtime
 from avocado.utils import process
 
 
@@ -352,6 +353,23 @@ class gdbtest(test.Test):
         listening_line = "Listening on port %s\n" % s.port
         self.assertIn(listening_line, stderr_lines)
 
+    def test_server_stderr_redirected(self):
+        s = gdb.GDBServer(runtime.GDBSERVER_PATH)
+        if not s.redirected_stderr:
+            s.exit()
+            return
+
+        self.log.info('Testing server stderr redirection')
+        c = gdb.GDB()
+        c.connect(s.port)
+        c.set_file(self.return99_binary_path)
+        c.run()
+        s.exit()
+
+        # only thing in stderr should be the output generated by return99
+        stderr = open(s.stderr_path, 'r').read()
+        self.assertEqual("testing output to stderr\n", stderr)
+
     def test_server_stdout(self):
         self.log.info('Testing server stdout/stderr collection')
         s = gdb.GDBServer()
@@ -400,5 +418,6 @@ class gdbtest(test.Test):
         self.test_interactive_args()
         self.test_exit_status()
         self.test_server_stderr()
+        self.test_server_stderr_redirected()
         self.test_server_stdout()
         self.test_interactive_stdout()