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RFA: [lynxos] gdbserver hangs when killing inferior from GDB
- From: Joel Brobecker <brobecker at adacore dot com>
- To: gdb-patches at sourceware dot org
- Date: Mon, 21 Dec 2015 19:17:56 +0400
- Subject: RFA: [lynxos] gdbserver hangs when killing inferior from GDB
- Authentication-results: sourceware.org; auth=none
With any program under GDBserver control on LynxOS, killing
the program from the debugger (using the "kill" command) causes
GDBserver to properly kill the inferior but GDBserver then hangs.
This change of behavior occured after the following change was
Date: Mon Nov 30 16:05:27 2015 +0000
Subject: gdbserver: don't exit until GDB disconnects
One of the changes introduced by the commit above is that
process_serial_event no longer calls exit after handling
the vKill packet. Instead, what happens is that we wait
until captured_main finds that we no longer have any inferior
to debug, at which point it throws_quit. This (normal) exception
is then expected to propagate all the way to the exception handle
in function "main", which calls exit.
However, before the exception gets propagated, the cleanups
are first executed, and one of the cleanups in question is
detach_or_kill_for_exit_cleanup, which was put in place by
captured_main. detach_or_kill_for_exit_cleanup is basically
a wrapper around detach_or_kill_for_exit, which iterates
over all inferiors, and kills them all.
In our case, we have only one inferior, which we have already
killed during the handling for the "vKill" packet. Unfortunately,
we did not properly clean our internal data for that inferior up,
and so detach_or_kill_for_exit thinks that we still have one inferior,
and therefore tries to kill it. This results in lynx_kill being
called, doing the following:
lynx_ptrace (PTRACE_KILL, ptid, 0, 0, 0);
lynx_wait (ptid, &status, 0);
The hang is caused by the call to lynx_wait, which waits for
an event from a process which does not exist...
This patch fixes the issue by enhancing lynx_mourn to clean
the threads and process list up.
* lynx-low.c (lynx_delete_thread_callback): New function.
(lynx_mourn): Properly delete our process and all of its
threads. Remove call to clear_inferiors.
Tested on LynxOS using AdaCore's gdb-testsuite.
OK to push?
gdb/gdbserver/lynx-low.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/gdb/gdbserver/lynx-low.c b/gdb/gdbserver/lynx-low.c
index 2940ce5..2821ff0 100644
@@ -546,16 +546,36 @@ lynx_detach (int pid)
+/* A callback for find_inferior which removes from the thread list
+ all threads belonging to process PROC. */
+lynx_delete_thread_callback (struct inferior_list_entry *entry, void *proc)
+ struct process_info *process = (struct process_info *) proc;
+ if (ptid_get_pid (entry->id) == pid_of (process))
+ struct thread_info *thr = find_thread_ptid (entry->id);
+ remove_thread (thr);
+ return 0;
/* Implement the mourn target_ops method. */
lynx_mourn (struct process_info *proc)
+ find_inferior (&all_threads, lynx_delete_thread_callback, proc);
/* Free our private data. */
proc->priv = NULL;
- clear_inferiors ();
+ remove_process (proc);
/* Implement the join target_ops method. */