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Workaround remote targets that report an empty list to qfThreadInfo

Browse Source 
In https://sourceware.org/ml/gdb-patches/2014-10/msg00652.html, Sandra
shows a target that was broken by the recent update_thread_list
optimization:

 (gdb) target remote qa8-centos32-cs:10514
 ...
 (gdb) continue
 Continuing.
 Cannot execute this command without a live selected thread.
 (gdb)

The error means that the current thread is in "exited" state when the
continue command is processed.  The root of the problem was found
here:

 > Sending packet: $Hg0#df...Packet received:
 ...
 > Sending packet: $?#3f...Packet received: S00
 > Sending packet: $qfThreadInfo#bb...Packet received: l
 > Sending packet: $Hc-1#09...Packet received:
 > Sending packet: $qC#b4...Packet received: unset

This target doesn't really support threads (no thread indication in
stop reply packets; no support for qC), but then supports
qfThreadInfo, and returns an empty thread list to GDB.

See https://sourceware.org/ml/gdb-patches/2014-10/msg00665.html for
why the target does that.

As remote_update_thread_list deletes threads from GDB's list that are
not found in the thread list that the target reports, the result is
that GDB deletes the "fake" main thread that GDB added itself.  (As
that thread is currently selected, it is marked "exited" instead of
being deleted straight away.)

This commit avoids deleting the main thread in this scenario.

gdb/
2014-10-27  Pedro Alves  <palves@redhat.com>

	* remote.c (remote_thread_alive): New, factored out from ...
	(remote_thread_alive): ... this.
	(remote_update_thread_list): Bail out before deleting threads if
	the target returned an empty list, and, the current thread has a
	magic/fake ptid.
This commit is contained in:
Pedro Alves 2014-10-28 11:35:10 +00:00
parent 708d7d0d11
commit 7d1a114c44
2 changed files with 40 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
gdb/ChangeLog
View File

@ -1,3 +1,11 @@
2014-10-27 Pedro Alves <palves@redhat.com>
* remote.c (remote_thread_alive): New, factored out from ...
(remote_thread_alive): ... this.
(remote_update_thread_list): Bail out before deleting threads if
the target returned an empty list, and, the current thread has a
magic/fake ptid.
2014-10-27 Pedro Alves <palves@redhat.com>
* infrun.c (handle_signal_stop): Also skip handlers when a random

35
gdb/remote.c
View File

@ -1842,11 +1842,11 @@ set_general_process (void)
}
/* Return nonzero if the thread PTID is still alive on the remote
system. */
/* Return nonzero if this is the main thread that we made up ourselves
to model non-threaded targets as single-threaded. */
static int
remote_thread_alive (struct target_ops *ops, ptid_t ptid)
remote_thread_always_alive (struct target_ops *ops, ptid_t ptid)
{
struct remote_state *rs = get_remote_state ();
char *p, *endp;
@ -1861,6 +1861,23 @@ remote_thread_alive (struct target_ops *ops, ptid_t ptid)
multi-threading. */
return 1;
return 0;
}
/* Return nonzero if the thread PTID is still alive on the remote
system. */
static int
remote_thread_alive (struct target_ops *ops, ptid_t ptid)
{
struct remote_state *rs = get_remote_state ();
char *p, *endp;
/* Check if this is a thread that we made up ourselves to model
non-threaded targets as single-threaded. */
if (remote_thread_always_alive (ops, ptid))
return 1;
p = rs->buf;
endp = rs->buf + get_remote_packet_size ();
@ -2780,6 +2797,18 @@ remote_update_thread_list (struct target_ops *ops)
got_list = 1;
if (VEC_empty (thread_item_t, context.items)
&& remote_thread_always_alive (ops, inferior_ptid))
{
/* Some targets don't really support threads, but still
reply an (empty) thread list in response to the thread
listing packets, instead of replying "packet not
supported". Exit early so we don't delete the main
thread. */
do_cleanups (old_chain);
return;
}
/* CONTEXT now holds the current thread list on the remote
target end. Delete GDB-side threads no longer found on the
target. */