RFC: Do not try g-packet-guess algorithm on exited targets

Daniel Jacobowitz
2008-11-23T21:15:47Z

We got a bug report indicating that gdbserver --multi didn't work on
MIPS. We'd connect to the target, try to read the XML description -
gdbserver reports an error because there's no process yet - and then
try to guess the description from the g packet length instead. Of
course we can't do that; there's no process yet.

This patch fixes the problem. We try qXfer on connection, then try
'g' only if (A) there was no XML description, and (B) there is a
running process, and (C) we are not in non-stop mode; assume that
non-stop targets can provide a description explicitly.

Pedro, could you take a look at this before I commit it? Tested on
x86 with various local changes to make sure the new code was covered;
it fixes ext-attach.exp there. I'll try it on MIPS now.

--
Daniel Jacobowitz
CodeSourcery

2008-11-23 Daniel Jacobowitz <dan@codesourcery.com>

PR gdb/2474
* remote.c (remote_read_description_p): New function.
(struct remote_state): New field tdesc_no_register_access.
(remote_start_remote): Try to fetch the target description without
any register access, then try with register access if the target
is running.
(remote_read_description): Honor tdesc_no_register_access.

Index: remote.c
===================================================================
RCS file: /cvs/src/src/gdb/remote.c,v
retrieving revision 1.329
diff -u -p -r1.329 remote.c
--- remote.c 19 Nov 2008 14:45:09 -0000 1.329
+++ remote.c 23 Nov 2008 21:09:02 -0000
@@ -234,6 +234,8 @@ static void remote_async_get_pending_eve

static void remote_terminal_ours (void);

+static int remote_read_description_p (struct target_ops *target);
+
/* The non-stop remote protocol provisions for one pending stop reply.
This is where we keep it until it is acknowledged. */

@@ -303,6 +305,10 @@ struct remote_state

/* True if the stub reports support for vCont;t. */
int support_vCont_t;
+
+ /* True if we are just connecting, and should not try fetching registers
+ yet. */
+ int tdesc_no_register_access;
};

/* Returns true if the multi-process extensions are in effect. */
@@ -2549,15 +2555,19 @@ remote_start_remote (struct ui_out *uiou
getpkt (&rs->buf, &rs->buf_size, 0);
}

+ /* Next, if the target can specify a description, read it. We do
+ this before anything involving memory or registers. At this
+ point, do not try to read registers from the target - it might
+ not be running, or it might be running and not stopped. */
+ rs->tdesc_no_register_access = 1;
+ target_find_description ();
+ rs->tdesc_no_register_access = 0;
+
/* On OSs where the list of libraries is global to all
processes, we fetch them early. */
if (gdbarch_has_global_solist (target_gdbarch))
solib_add (NULL, args->from_tty, args->target, auto_solib_add);

- /* Next, if the target can specify a description, read it. We do
- this before anything involving memory or registers. */
- target_find_description ();
-
if (non_stop)
{
if (!rs->non_stop_aware)
@@ -2643,6 +2653,17 @@ remote_start_remote (struct ui_out *uiou

get_offsets (); /* Get text, data & bss offsets. */

+ /* If we could not find a description using qXfer, and we know
+ how to do it some other way, try again. This is not
+ supported for non-stop; it could be, but it is tricky if
+ there are no stopped threads when we connect. */
+ if (remote_read_description_p (args->target)
+ && gdbarch_target_desc (target_gdbarch) == NULL)
+ {
+ target_clear_description ();
+ target_find_description ();
+ }
+
/* Use the previously fetched status. */
gdb_assert (wait_status != NULL);
strcpy (rs->buf, wait_status);
@@ -7852,12 +7873,32 @@ register_remote_g_packet_guess (struct g
VEC_safe_push (remote_g_packet_guess_s, data->guesses, &new_guess);
}

+/* Return 1 if remote_read_description would do anything on this target
+ and architecture, 0 otherwise. */
+
+static int
+remote_read_description_p (struct target_ops *target)
+{
+ struct remote_g_packet_data *data
+ = gdbarch_data (target_gdbarch, remote_g_packet_data_handle);
+
+ if (!VEC_empty (remote_g_packet_guess_s, data->guesses))
+ return 1;
+
+ return 0;
+}
+
static const struct target_desc *
remote_read_description (struct target_ops *target)
{
+ struct remote_state *rs = get_remote_state ();
struct remote_g_packet_data *data
= gdbarch_data (target_gdbarch, remote_g_packet_data_handle);

+ /* Do not try this during initial connection. */
+ if (rs->tdesc_no_register_access)
+ return NULL;
+
if (!VEC_empty (remote_g_packet_guess_s, data->guesses))
{
struct remote_g_packet_guess *guess;