Re: [RFA] Only try to load libthread_db when we load libpthread.

[Doug Evans <dje@google.com>]

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On Fri, Oct 7, 2011 at 4:09 AM, Pedro Alves <pedro@codesourcery.com> wrote:
> Well, at least things should work the same as before, which IMO
> is good thing as it makes this change an optimization only.

That's the intent.

>> Blech, I forgot one bit of cleanup.
>> Revised patch attached.
>
> Still breaks activating thread_db when debugging cores of
> static executables.

Used wrong sandbox for the before case, sigh.

[...]

> Did you try this suggestion?:
>
>> I think we'll no longer activate thread_db when debugging core
>> files of static executables (e.g., a core of gdb.threads/staticthreads).
>> It works with live debugging since we call check_for_thread_db
>> from linux_child_post_attach/linux_child_post_startup_inferior.
>> Maybe moving that to an inferior_created observer in
>> linux-thread-db.c would work.

It turns out things work today accidentally.
At least I doubt it's by design. :-)
My previous patch didn't work because it skipped calling
check_for_thread_db when the new_objfile observer was called for
vsyscall (which incidentally is called by the inferior_created
observer for vsyscall, heh).
[Which explains why it didn't surprise me when my before-test failed,
that's a pretty unexpected way to load libthread_db.]

How about this.

2011-10-09  Doug Evans  <dje@google.com>

        * linux-thread-db.c (thread_db_new_objfile): Only try to load
        libthread_db when we load libpthread.
        (thread_db_inferior_created): New function.
        (_initialize_thread_db): Attach inferior_created observer.

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2011-10-09  Doug Evans  <dje@google.com>

	* linux-thread-db.c (thread_db_new_objfile): Only try to load
	libthread_db when we load libpthread.
	(thread_db_inferior_created): New function.
	(_initialize_thread_db): Attach inferior_created observer.

Index: linux-thread-db.c
===================================================================
RCS file: /cvs/src/src/gdb/linux-thread-db.c,v
retrieving revision 1.91
diff -u -p -r1.91 linux-thread-db.c
--- linux-thread-db.c	13 Sep 2011 19:27:01 -0000	1.91
+++ linux-thread-db.c	10 Oct 2011 03:52:27 -0000
@@ -1077,16 +1077,32 @@ check_for_thread_db (void)
     return;
 }
 
+/* This function is called via the new_objfile observer.  */
+
 static void
 thread_db_new_objfile (struct objfile *objfile)
 {
   /* This observer must always be called with inferior_ptid set
      correctly.  */
 
-  if (objfile != NULL)
+  if (objfile != NULL
+      /* Only check for thread_db if we loaded libpthread.
+	 For dynamically linked executables, libpthread can be near the end
+	 of the list of shared libraries to load, and in an app of several
+	 thousand shared libraries, this can otherwise be painful.  */
+      && libpthread_name_p (objfile->name))
     check_for_thread_db ();
 }
 
+/* This function is called via the inferior_created observer.
+   This handles the case of debugging statically linked executables.  */
+
+static void
+thread_db_inferior_created (struct target_ops *target, int from_tty)
+{
+  check_for_thread_db ();
+}
+
 /* Attach to a new thread.  This function is called when we receive a
    TD_CREATE event or when we iterate over all threads and find one
    that wasn't already in our list.  Returns true on success.  */
@@ -1845,4 +1861,9 @@ When non-zero, libthread-db debugging is
 
   /* Add ourselves to objfile event chain.  */
   observer_attach_new_objfile (thread_db_new_objfile);
+
+  /* Add ourselves to inferior_created event chain.
+     This is needed to handle debugging statically linked programs where
+     the new_objfile observer won't get called for libpthread.  */
+  observer_attach_inferior_created (thread_db_inferior_created);
 }