[RFA/gdbserver/LynxOS]: Incomplete thread list after --attach

[Joel Brobecker <brobecker@adacore.com>]

Hello,

The current implementation is forgetting to populate the thread list
when attaching to the process. This results in an incomplete list of
threads when debugging a threaded program.

Unfortunately, as the added comments hints, there appears to be
no way of getting the list of threads via ptrace, other than by
spawning the "ps" command, and parsing its output. Not great,
but it appears to be the best we can do.  This method was actually
inspired by looking at old code which did exactly that.

gdb/gdbserver/ChangeLog:

        * lynx-low.c (lynx_add_threads_after_attach): New function.
        (lynx_attach): Remove call to add_thread.  Add call to
        lynx_add_threads_after_attach instead.

Tested on various LynxOS platforms.  OK to commit?

Thanks,
-- 
Joel

---
 gdb/gdbserver/lynx-low.c |   38 +++++++++++++++++++++++++++++++++++++-
 1 files changed, 37 insertions(+), 1 deletions(-)

diff --git a/gdb/gdbserver/lynx-low.c b/gdb/gdbserver/lynx-low.c
index 3c75b62..09c214e 100644
--- a/gdb/gdbserver/lynx-low.c
+++ b/gdb/gdbserver/lynx-low.c
@@ -262,6 +262,42 @@ lynx_create_inferior (char *program, char **allargs)
   return pid;
 }
 
+/* Assuming we've just attached to a running inferior whose pid is PID,
+   add all threads runnnig in that process.  */
+
+static void
+lynx_add_threads_after_attach (int pid)
+{
+  /* Ugh!  There appears to be no way to get the list of threads
+     in the program we just attached to.  So get the list by calling
+     the "ps" command.  This is only needed now, as we will then
+     keep the thread list up to date thanks to thread creation and
+     exit notifications.  */
+  FILE *f;
+  char buf[256];
+  int thread_pid, thread_tid;
+
+  f = popen ("ps atx", "r");
+  if (f == NULL)
+    perror_with_name ("Cannot get thread list");
+
+  while (fgets (buf, sizeof (buf), f) != NULL)
+    if ((sscanf (buf, "%d %d", &thread_pid, &thread_tid) == 2
+	 && thread_pid == pid))
+    {
+      ptid_t thread_ptid = lynx_ptid_build (pid, thread_tid);
+
+      if (!find_thread_ptid (thread_ptid))
+	{
+	  lynx_debug ("New thread: (pid = %d, tid = %d)",
+		      pid, thread_tid);
+	  add_thread (thread_ptid, NULL);
+	}
+    }
+
+  pclose (f);
+}
+
 /* Implement the attach target_ops method.  */
 
 static int
@@ -274,7 +310,7 @@ lynx_attach (unsigned long pid)
 	   strerror (errno), errno);
 
   lynx_add_process (pid, 1);
-  add_thread (ptid, NULL);
+  lynx_add_threads_after_attach (pid);
 
   return 0;
 }
-- 
1.7.0.4