(Ada) crash connecting to TSIM simulator

Connecting to a TSIM simulator over the remote protocol causes GDB
to crash with the following failed assertion:

    (gdb) tar remote :1234
    Remote debugging using :1234
    /[...]/gdb/ravenscar-thread.c:182: internal-error: ravenscar_update_inferior_ptid: Assertion `!is_ravenscar_task (inferior_ptid)' failed.
    A problem internal to GDB has been detected,
    further debugging may prove unreliable.
    Quit this debugging session? (y or n) y

What happens is the following. Upon connection to the target, GDB
sends a 'qfThreadInfo' query, which is the query asking the target
for the ID of the first thread, and TSIM replies 'm0':

    Sending packet: $qfThreadInfo#bb...Ack
    Packet received: m0

As a result of this, GDB takes the '0' as the TID, and because of it,
constructs a ptid whose value is {42000, 0, 0}. This trips our
!is_ravenscar_task check, because all it does to identify threads
corresponding to ravenscar tasks is that their lwp is null, because
that's how we construct their ptid.

But this is unfortunatly not sufficient when debugging with TSIM,
because the thread ID that TSIM returns causes the creation of
a ptid whose lwp is zero, which matches the current identification
scheme and yet is clearly not a ravenscar task.

The fix is to also make sure that the ptid's tid field is nonzero.

gdb/ChangeLog:

        * ravenscar-thread.c (is_ravenscar_task): Also verify that
        the ptid's TID is nonzero.

1 files changed, 8 insertions, 2 deletions

diff --git a/gdb/ravenscar-thread.c b/gdb/ravenscar-thread.c
index e792227..00593b8 100644
--- a/gdb/ravenscar-thread.c
+++ b/gdb/ravenscar-thread.c
@@ -101,8 +101,14 @@ static void ravenscar_inferior_created (struct target_ops *target,
 static int
 is_ravenscar_task (ptid_t ptid)
 {
-  /* By construction, ravenscar tasks have their LWP set to zero.  */
-  return ptid_get_lwp (ptid) == 0;
+  /* By construction, ravenscar tasks have their LWP set to zero.
+     Also make sure that the TID is nonzero, as some remotes, when
+     asked for the list of threads, will return the first thread
+     as having its TID set to zero.  For instance, TSIM version
+     2.0.48 for LEON3 sends 'm0' as a reply to the 'qfThreadInfo'
+     query, which the remote protocol layer then treats as a thread
+     whose TID is 0.  This is obviously not a ravenscar task.  */
+  return ptid_get_lwp (ptid) == 0 && ptid_get_tid (ptid) != 0;
 }
 
 /* Given PTID, which can be either a ravenscar task or a CPU thread,