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

[Doug Evans <dje@google.com>]

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On Mon, Oct 10, 2011 at 11:22 AM, Pedro Alves <pedro@codesourcery.com> wrote:
> This version goes back to breaking the "file right_executable" core
> or attach cases (with static binaries) that the previous patch
> fixed.  :-)
> [...]
> (gdb -c core; file exec).

That scenario I hadn't thought of.
Thanks, at least the code will be there for a documented reason.
Note that the non-static case of that sequence was and still is broken.

I checked this in.

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

        * linux-thread-db.c (thread_db_new_objfile): Only try to load
        libthread_db when we load libpthread or the main symbol file.
        (thread_db_inferior_created): New function.
        (_initialize_thread_db): Attach inferior_created observer.
        * linux-nat.c (linux_child_post_attach): Remove call to
        check_for_thread_db.
        (linux_child_post_startup_inferior): Ditto.
        * objfiles.h (OBJF_MAINLINE): Define.
        * symfile.c (symbol_file_add_with_addrs_or_offsets): Pass it to
        allocate_objfile when appropriate.

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

	* linux-thread-db.c (thread_db_new_objfile): Only try to load
	libthread_db when we load libpthread or the main symbol file.
	(thread_db_inferior_created): New function.
	(_initialize_thread_db): Attach inferior_created observer.
	* linux-nat.c (linux_child_post_attach): Remove call to
	check_for_thread_db.
	(linux_child_post_startup_inferior): Ditto.
	* objfiles.h (OBJF_MAINLINE): Define.
	* symfile.c (symbol_file_add_with_addrs_or_offsets): Pass it to
	allocate_objfile when appropriate.

Index: linux-nat.c
===================================================================
RCS file: /cvs/src/src/gdb/linux-nat.c,v
retrieving revision 1.216
diff -u -p -r1.216 linux-nat.c
--- linux-nat.c	7 Oct 2011 12:06:46 -0000	1.216
+++ linux-nat.c	11 Oct 2011 02:44:46 -0000
@@ -571,7 +571,6 @@ static void
 linux_child_post_attach (int pid)
 {
   linux_enable_event_reporting (pid_to_ptid (pid));
-  check_for_thread_db ();
   linux_enable_tracesysgood (pid_to_ptid (pid));
 }
 
@@ -579,7 +578,6 @@ static void
 linux_child_post_startup_inferior (ptid_t ptid)
 {
   linux_enable_event_reporting (ptid);
-  check_for_thread_db ();
   linux_enable_tracesysgood (ptid);
 }
 
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	11 Oct 2011 02:44:46 -0000
@@ -1077,16 +1077,37 @@ 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,
+	 or if this is the main symbol file.
+	 We need to check OBJF_MAINLINE to handle the case of debugging
+	 a statically linked executable AND the symbol file is specified AFTER
+	 the core file is loaded (e.g., gdb -c core ; file foo).
+	 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.  */
+      && ((objfile->flags & OBJF_MAINLINE) != 0
+	  || 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 +1866,9 @@ 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);
 }
Index: objfiles.h
===================================================================
RCS file: /cvs/src/src/gdb/objfiles.h,v
retrieving revision 1.85
diff -u -p -r1.85 objfiles.h
--- objfiles.h	14 Jun 2011 16:49:41 -0000	1.85
+++ objfiles.h	11 Oct 2011 02:44:46 -0000
@@ -196,7 +196,8 @@ struct objfile
 
     CORE_ADDR addr_low;
 
-    /* Some flag bits for this objfile.  */
+    /* Some flag bits for this objfile.
+       The values are defined by OBJF_*.  */
 
     unsigned short flags;
 
@@ -434,6 +435,11 @@ struct objfile
 
 #define OBJF_PSYMTABS_READ (1 << 4)
 
+/* Set if this is the main symbol file
+   (as opposed to symbol file for dynamically loaded code).  */
+
+#define OBJF_MAINLINE (1 << 5)
+
 /* The object file that contains the runtime common minimal symbols
    for SunOS4.  Note that this objfile has no associated BFD.  */
 
Index: symfile.c
===================================================================
RCS file: /cvs/src/src/gdb/symfile.c,v
retrieving revision 1.316
diff -u -p -r1.316 symfile.c
--- symfile.c	29 Sep 2011 02:04:25 -0000	1.316
+++ symfile.c	11 Oct 2011 02:44:46 -0000
@@ -1081,6 +1081,7 @@ symbol_file_add_with_addrs_or_offsets (b
   struct cleanup *my_cleanups;
   const char *name = bfd_get_filename (abfd);
   const int from_tty = add_flags & SYMFILE_VERBOSE;
+  const int mainline = add_flags & SYMFILE_MAINLINE;
   const int should_print = ((from_tty || info_verbose)
 			    && (readnow_symbol_files
 				|| (add_flags & SYMFILE_NO_READ) == 0));
@@ -1097,12 +1098,12 @@ symbol_file_add_with_addrs_or_offsets (b
      interactively wiping out any existing symbols.  */
 
   if ((have_full_symbols () || have_partial_symbols ())
-      && (add_flags & SYMFILE_MAINLINE)
+      && mainline
       && from_tty
       && !query (_("Load new symbol table from \"%s\"? "), name))
     error (_("Not confirmed."));
 
-  objfile = allocate_objfile (abfd, flags);
+  objfile = allocate_objfile (abfd, flags | (mainline ? OBJF_MAINLINE : 0));
   discard_cleanups (my_cleanups);
 
   if (parent)