RFC: Initialize libthread_db at the right time

[Daniel Jacobowitz <drow at false dot org>]

We've had some recurring problems debugging statically linked executables
using libthread_db; this patch is the first of several fixes for that.
This doesn't do much; it just splits the check out from the new_objfile
hook, and calls it from target_post_attach and target_post_startup_inferior
in the Linux native target.

Earlier versions of this patch used an observer instead, which was silly
of me; we only want to do this when we're sitting on top of the Linux
native target, not when we're on top of e.g. the remote target.  This
mostly fixes the not-enabling-libthread_db-when-we-should-be class of
problems; there's still one gross hack in remote.c which avoids
calling the new objfile hook for remote targets, but that's a mess
for another day.

Any comments?  Otherwise, I'll commit this in a few days.  It handles
LinuxThreads, but NPTL needs a little push (coming up next).

-- 
Daniel Jacobowitz
CodeSourcery

2006-02-27  Daniel Jacobowitz  <dan@codesourcery.com>

	* linux-thread-db.c: Include "linux-nat.h".
	(check_for_thread_db): New function, split out from
	thread_db_new_objfile.  Remove dead check for active
	thread_db on inapplicable targets.
	(thread_db_new_objfile): Call check_for_thread_db.
	* Makefile.in (linux-thread-db.o): Update.
	* linux-nat.c (child_post_attach): Call check_for_thread_db.
	(linux_child_post_startup_inferior): Likewise.
	(lin_lwp_attach_lwp): Call target_post_attach instead of
	child_post_attach.
	* linux-nat.h (check_for_thread_db): New prototype.

Index: src/gdb/linux-thread-db.c
===================================================================
--- src.orig/gdb/linux-thread-db.c	2006-02-27 12:44:41.000000000 -0500
+++ src/gdb/linux-thread-db.c	2006-02-27 14:36:30.000000000 -0500
@@ -37,6 +37,7 @@
 #include "regcache.h"
 #include "solib-svr4.h"
 #include "gdbcore.h"
+#include "linux-nat.h"
 
 #ifdef HAVE_GNU_LIBC_VERSION_H
 #include <gnu/libc-version.h>
@@ -626,59 +627,49 @@ check_thread_signals (void)
 #endif
 }
 
-static void
-thread_db_new_objfile (struct objfile *objfile)
+/* Check whether thread_db is usable.  This function is called when
+   an inferior is created (or otherwise acquired, e.g. attached to)
+   and when new shared libraries are loaded into a running process.  */
+
+void
+check_for_thread_db (void)
 {
   td_err_e err;
+  static int already_loaded;
 
   /* First time through, report that libthread_db was successfuly
      loaded.  Can't print this in in thread_db_load as, at that stage,
-     the interpreter and it's console haven't started.  The real
-     problem here is that libthread_db is loaded too early - it should
-     only be loaded when there is a program to debug.  */
-  {
-    static int dejavu;
-    if (!dejavu)
-      {
-	Dl_info info;
-	const char *library = NULL;
-	/* Try dladdr.  */
-	if (dladdr ((*td_ta_new_p), &info) != 0)
-	  library = info.dli_fname;
-	/* Try dlinfo?  */
-	if (library == NULL)
-	  /* Paranoid - don't let a NULL path slip through.  */
-	  library = LIBTHREAD_DB_SO;
-	printf_unfiltered (_("Using host libthread_db library \"%s\".\n"),
-			   library);
-	dejavu = 1;
-      }
-  }
+     the interpreter and it's console haven't started.  */
 
-  /* Don't attempt to use thread_db on targets which can not run
-     (core files).  */
-  if (objfile == NULL || !target_has_execution)
+  if (!already_loaded)
     {
-      /* All symbols have been discarded.  If the thread_db target is
-         active, deactivate it now.  */
-      if (using_thread_db)
-	{
-	  gdb_assert (proc_handle.pid == 0);
-	  unpush_target (&thread_db_ops);
-	  using_thread_db = 0;
-	}
+      Dl_info info;
+      const char *library = NULL;
+      if (dladdr ((*td_ta_new_p), &info) != 0)
+	library = info.dli_fname;
+
+      /* Try dlinfo?  */
+
+      if (library == NULL)
+	/* Paranoid - don't let a NULL path slip through.  */
+	library = LIBTHREAD_DB_SO;
 
-      goto quit;
+      printf_unfiltered (_("Using host libthread_db library \"%s\".\n"),
+			 library);
+      already_loaded = 1;
     }
 
   if (using_thread_db)
     /* Nothing to do.  The thread library was already detected and the
        target vector was already activated.  */
-    goto quit;
+    return;
 
-  /* Initialize the structure that identifies the child process.  Note
-     that at this point there is no guarantee that we actually have a
-     child process.  */
+  /* Don't attempt to use thread_db on targets which can not run
+     (executables not running yet, core files) for now.  */
+  if (!target_has_execution)
+    return;
+
+  /* Initialize the structure that identifies the child process.  */
   proc_handle.pid = GET_PID (inferior_ptid);
 
   /* Now attempt to open a connection to the thread library.  */
@@ -705,8 +696,14 @@ thread_db_new_objfile (struct objfile *o
 	       thread_db_err_str (err));
       break;
     }
+}
+
+static void
+thread_db_new_objfile (struct objfile *objfile)
+{
+  if (objfile != NULL)
+    check_for_thread_db ();
 
-quit:
   if (target_new_objfile_chain)
     target_new_objfile_chain (objfile);
 }
Index: src/gdb/Makefile.in
===================================================================
--- src.orig/gdb/Makefile.in	2006-02-27 14:16:21.000000000 -0500
+++ src/gdb/Makefile.in	2006-02-27 14:36:30.000000000 -0500
@@ -2198,7 +2198,7 @@ linux-nat.o: linux-nat.c $(defs_h) $(inf
 linux-thread-db.o: linux-thread-db.c $(defs_h) $(gdb_assert_h) \
 	$(gdb_proc_service_h) $(gdb_thread_db_h) $(bfd_h) $(exceptions_h) \
 	$(gdbthread_h) $(inferior_h) $(symfile_h) $(objfiles_h) $(target_h) \
-	$(regcache_h) $(solib_svr4_h) $(gdbcore_h)
+	$(regcache_h) $(solib_svr4_h) $(gdbcore_h) $(linux_nat_h)
 lynx-nat.o: lynx-nat.c $(defs_h) $(frame_h) $(inferior_h) $(target_h) \
 	$(gdbcore_h) $(regcache_h)
 m2-exp.o: m2-exp.c $(defs_h) $(gdb_string_h) $(expression_h) $(language_h) \
Index: src/gdb/linux-nat.c
===================================================================
--- src.orig/gdb/linux-nat.c	2006-02-27 12:47:52.000000000 -0500
+++ src/gdb/linux-nat.c	2006-02-27 14:36:30.000000000 -0500
@@ -334,12 +334,14 @@ void
 child_post_attach (int pid)
 {
   linux_enable_event_reporting (pid_to_ptid (pid));
+  check_for_thread_db ();
 }
 
 static void
 linux_child_post_startup_inferior (ptid_t ptid)
 {
   linux_enable_event_reporting (ptid);
+  check_for_thread_db ();
 }
 
 int
@@ -963,7 +965,7 @@ lin_lwp_attach_lwp (ptid_t ptid, int ver
       gdb_assert (pid == GET_LWP (ptid)
 		  && WIFSTOPPED (status) && WSTOPSIG (status));
 
-      child_post_attach (pid);
+      target_post_attach (pid);
 
       lp->stopped = 1;
 
Index: src/gdb/linux-nat.h
===================================================================
--- src.orig/gdb/linux-nat.h	2006-02-27 12:56:19.000000000 -0500
+++ src/gdb/linux-nat.h	2006-02-27 14:36:30.000000000 -0500
@@ -65,6 +65,8 @@ struct lwp_info
   struct lwp_info *next;
 };
 
+/* Attempt to initialize libthread_db.  */
+void check_for_thread_db (void);
 
 /* Find process PID's pending signal set from /proc/pid/status.  */
 void linux_proc_pending_signals (int pid, sigset_t *pending, sigset_t *blocked, sigset_t *ignored);