[PATCHv2 3/3] gdb/python: add TargetConnection.send_remote_packet method

[Andrew Burgess <andrew.burgess@embecosm.com>]

This commit adds a new method to the gdb.TargetConnection object type:
'send_remote_packet'.  This new method is equivalent to the 'maint
packet' CLI command, it allows a custom packet to be sent to a remote
target.

Not all gdb.TargetConnection instances will support
send_remote_packet, e.g. the 'native' target doesn't.  If the
send_remote_packet method is invoked on a TargetConnection that is not
'remote' or 'extended-remote' then an exception is thrown.

The result of calling TargetConnection.send_remote_packet is a string
containing the reply that came from the remote.
---
 gdb/NEWS                                    |  6 ++
 gdb/doc/gdb.texinfo                         |  1 +
 gdb/doc/python.texi                         | 22 ++++-
 gdb/python/py-connection.c                  | 90 +++++++++++++++++++++
 gdb/testsuite/gdb.python/py-send-packet.c   | 22 +++++
 gdb/testsuite/gdb.python/py-send-packet.exp | 55 +++++++++++++
 gdb/testsuite/gdb.python/py-send-packet.py  | 82 +++++++++++++++++++
 7 files changed, 277 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.python/py-send-packet.c
 create mode 100644 gdb/testsuite/gdb.python/py-send-packet.exp
 create mode 100644 gdb/testsuite/gdb.python/py-send-packet.py

diff --git a/gdb/NEWS b/gdb/NEWS
index 43b81df526d..a567098d13a 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -61,6 +61,12 @@ maint show internal-warning backtrace
   ** New gdb.connections() function that returns a list of all
      currently active connections.
 
+  ** New gdb.TargetConnection.send_remote_packet(STRING) method.  This
+     is equivalent to the existing 'maint packet' CLI command; it
+     allows a user specified packet to be sent to the remote target.
+     If this method is called on a TargetConnection that is not of
+     type 'remote' or 'extended-remote' then an exception is thrown.
+
 *** Changes in GDB 11
 
 * The 'set disassembler-options' command now supports specifying options
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 631a7c03b31..89cf86210ab 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -39269,6 +39269,7 @@
 error stream.  This is @samp{on} by default for @code{internal-error}
 and @samp{off} by default for @code{internal-warning}.
 
+@anchor{maint packet}
 @kindex maint packet
 @item maint packet @var{text}
 If @value{GDBN} is talking to an inferior via the serial protocol,
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index f81707eb002..6e8ab3a5a5c 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -5989,7 +5989,7 @@
 @code{gdb.Inferior.connection} attribute
 (@pxref{gdbpy_inferior_connection,,gdb.Inferior.connection}).
 
-A @code{gdb.TargetConnection} has the following method:
+A @code{gdb.TargetConnection} has the following methods:
 
 @defun TargetConnection.is_valid ()
 Return @code{True} if the @code{gdb.TargetConnection} object is valid,
@@ -6001,6 +6001,26 @@
 an exception if the connection is invalid.
 @end defun
 
+@kindex maint packet
+@defun TargetConnection.send_remote_packet (@var{packet})
+When the connection object is using @value{GDBN}'s remote serial
+protocol (@pxref{Remote Protocol}), i.e.@: the
+@code{TargetConnection.type} is @samp{remote} or
+@samp{extended-remote}, then this method sends @var{packet}, which
+should be a non-empty string, to the remote target and returns the
+response packet as a string.  For any other connection type, calling
+this method will throw a @code{gdb.error} exception.  If @var{packet}
+is not a string, or is the empty string, then an exception of type
+@code{gdb.error} is thrown.
+
+The prefix, suffix, and checksum (as required by the remote serial
+protocol) are automatically added to the outgoing packet, and removed
+from the incoming packet before the reply is returned.
+
+This is equivalent to the @code{maintenance packet} command
+(@pxref{maint packet}).
+@end defun
+
 A @code{gdb.TargetConnection} has the following read-only properties:
 
 @defvar TargetConnection.num
diff --git a/gdb/python/py-connection.c b/gdb/python/py-connection.c
index f75a8735148..43797d48a94 100644
--- a/gdb/python/py-connection.c
+++ b/gdb/python/py-connection.c
@@ -26,6 +26,8 @@
 #include "py-events.h"
 #include "py-event.h"
 #include "arch-utils.h"
+#include "remote.h"
+#include "charset.h"
 
 #include <map>
 
@@ -286,6 +288,90 @@ gdbpy_initialize_connection (void)
   return 0;
 }
 
+/* Set of callbacks used to implement gdb.send_remote_packet.  */
+
+struct py_send_packet_callbacks : public send_remote_packet_callbacks
+{
+  /* Constructor, initialise the result to None.  */
+
+  py_send_packet_callbacks ()
+    : m_result (Py_None)
+  { /* Nothing.  */ }
+
+  /* There's nothing to do when the packet is sent.  */
+
+  void sending (const char *args) override
+  { /* Nothing.  */ }
+
+  /* When the result is returned create a Python string and assign this
+     into the result member variable.  */
+
+  void received (const gdb::char_vector &buf) override
+  {
+    /* Return None when we don't get back a useful result.  */
+    if (buf.data ()[0] != '\0')
+      m_result = gdbpy_ref<> (PyUnicode_Decode (buf.data (),
+						strlen (buf.data ()),
+						host_charset (), nullptr));
+  }
+
+  /* Get a reference to the result as a Python object.  */
+
+  gdbpy_ref<> result () const
+  {
+    return m_result;
+  }
+
+private:
+
+  /* A reference to a valid result value.  This is initialized in the
+     constructor, and so will always point to a valid value, even if this
+     is just None.  */
+
+  gdbpy_ref<> m_result;
+};
+
+/* Implement TargetConnection.send_remote_packet function.  Send a packet
+   to the target identified by SELF.  The connection must still be valid,
+   and must be a remote or extended-remote connection otherwise an
+   exception will be thrown.  */
+
+static PyObject *
+connpy_send_remote_packet (PyObject *self, PyObject *args, PyObject *kw)
+{
+  connection_object *conn = (connection_object *) self;
+
+  CONNPY_REQUIRE_VALID (conn);
+
+  static const char *keywords[] = {"packet", nullptr};
+  const char *packet_str = nullptr;
+
+  if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "s", keywords,
+					&packet_str))
+    return nullptr;
+
+  if (packet_str == nullptr || *packet_str == '\0')
+    {
+      PyErr_SetString (PyExc_ValueError, _("Invalid remote packet"));
+      return nullptr;
+    }
+
+  try
+    {
+      scoped_restore_current_thread restore_thread;
+      switch_to_target_no_thread (conn->target);
+
+      py_send_packet_callbacks callbacks;
+      send_remote_packet (packet_str, &callbacks);
+      return callbacks.result ().release ();
+    }
+  catch (const gdb_exception &except)
+    {
+      gdbpy_convert_exception (except);
+      return nullptr;
+    }
+}
+
 /* Global initialization for this file.  */
 
 void _initialize_py_connection ();
@@ -303,6 +389,10 @@ static PyMethodDef connection_object_methods[] =
   { "is_valid", connpy_is_valid, METH_NOARGS,
     "is_valid () -> Boolean.\n\
 Return true if this TargetConnection is valid, false if not." },
+  { "send_remote_packet", (PyCFunction) connpy_send_remote_packet,
+    METH_VARARGS | METH_KEYWORDS,
+    "send_remote_packet (PACKET) -> String\n\
+Send PACKET to a remote target, return the reply as a string." },
   { NULL }
 };
 
diff --git a/gdb/testsuite/gdb.python/py-send-packet.c b/gdb/testsuite/gdb.python/py-send-packet.c
new file mode 100644
index 00000000000..9811b15f06d
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-send-packet.c
@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2021 Free Software Foundation, Inc.
+
+   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 3 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 the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int
+main ()
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.python/py-send-packet.exp b/gdb/testsuite/gdb.python/py-send-packet.exp
new file mode 100644
index 00000000000..81001343f0c
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-send-packet.exp
@@ -0,0 +1,55 @@
+# Copyright (C) 2021 Free Software Foundation, Inc.
+
+# 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 3 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 the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test the gdb.TargetConnection.send_remote_packet API.  This is done
+# by connecting to a remote target and fetching the thread list in two
+# ways, first, we manually send the packets required to read the
+# thread list using gdb.TargetConnection.send_remote_packet, then we
+# compare the results to the thread list using the standard API calls.
+
+load_lib gdb-python.exp
+load_lib gdbserver-support.exp
+
+standard_testfile
+
+if {[skip_gdbserver_tests]} {
+    return 0
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
+    return -1
+}
+
+gdb_exit
+gdb_start
+
+if { [skip_python_tests] } {
+    return 0
+}
+
+# Make sure we're disconnected, in case we're testing with an
+# extended-remote board, therefore already connected.
+gdb_test "disconnect" ".*"
+
+gdbserver_run ""
+
+# Source the python script.
+set remote_python_file [gdb_remote_download host \
+			    ${srcdir}/${subdir}/${testfile}.py]
+gdb_test "source $remote_python_file" "Sourcing complete\\." \
+    "source ${testfile}.py script"
+
+# The test is actually written in the Python script.  Run it now.
+gdb_test "python run_send_packet_test()" "Send packet test passed"
diff --git a/gdb/testsuite/gdb.python/py-send-packet.py b/gdb/testsuite/gdb.python/py-send-packet.py
new file mode 100644
index 00000000000..f4dc5734057
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-send-packet.py
@@ -0,0 +1,82 @@
+# Copyright (C) 2021 Free Software Foundation, Inc.
+
+# 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 3 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 the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import xml.etree.ElementTree as ET
+import gdb
+
+# Make use of gdb.TargetConnection.send_remote_packet to fetch the
+# thread list from the remote target.
+#
+# Sending existing serial protocol packets like this is not a good
+# idea, there should be better ways to get this information using an
+# official API, this is just being used as a test case.
+#
+# Really, the send_remote_packet API would be used to send target
+# specific packets to the target, but these are, by definition, target
+# specific, so hard to test in a general testsuite.
+def get_thread_list_str():
+    start_pos = 0
+    thread_desc = ""
+    try:
+        while True:
+            conn = gdb.selected_inferior().connection
+            str = conn.send_remote_packet("qXfer:threads:read::%d,200" % start_pos)
+            start_pos += 200
+            c = str[0]
+            str = str[1:]
+            thread_desc += str
+            if c == "l":
+                break
+        return thread_desc
+    except:
+        return None
+
+
+# Use gdb.TargetConnection.send_remote_packet to manually fetch the
+# thread list, then extract the thread list using the gdb.Inferior and
+# gdb.InferiorThread API.  Compare the two results to ensure we
+# managed to successfully read the thread list from the remote.
+def run_send_packet_test():
+    # Find the IDs of all current threads.
+    all_threads = {}
+    for inf in gdb.inferiors():
+        for thr in inf.threads():
+            id = "p%x.%x" % (thr.ptid[0], thr.ptid[1])
+            all_threads[id] = False
+
+    # Now fetch the thread list from the remote, and parse the XML.
+    str = get_thread_list_str()
+    threads_xml = ET.fromstring(str)
+
+    # Look over all threads in the XML list and check we expected to
+    # find them, mark the ones we do find.
+    for thr in threads_xml:
+        id = thr.get("id")
+        if not id in all_threads:
+            raise "found unexpected thread in remote thread list"
+        else:
+            all_threads[id] = True
+
+    # Check that all the threads were found in the XML list.
+    for id in all_threads:
+        if not all_threads[id]:
+            raise "thread missingt from remote thread list"
+
+    # Test complete.
+    print("Send packet test passed")
+
+
+# Just to indicate the file was sourced correctly.
+print("Sourcing complete.")
-- 
2.25.4