http://sourceware.org/ml/gdb-patches/2010-02/msg00625.html

Subject: RFC: fix bug with std::terminate handler

I would appreciate comments on this patch.

This comes from an automatically-reported bug in the Red Hat bugzilla:

    https://bugzilla.redhat.com/show_bug.cgi?id=562975

call_function_by_hand installs a momentary breakpoint on std::terminate,

and then deletes it later.  However, this can cause a double deletion of

the breakpoint.  In the bug, the called function is dlopen, which causes

gdb to enter solib_add, which calls breakpoint_re_set, deleting the

momentary breakpoint.

This fix works by creating the momentary breakpoint with an internal

breakpoint number, and then trying to delete the breakpoint by number.

This bug does not always manifest in a crash.  In fact, I couldn't make

it crash here, but I could observe the problem under valgrind.

Built and regtested on x86-64 (compile farm).  I also manually verified

it using valgrind.

I think this patch is mildly ugly, due to the introduction of

set_momentary_breakpoint_at_pc_with_number.  However, in the absence of

comments, I plan to check it in after a reasonable waiting period.

Tom

2010-02-25  Tom Tromey  <tromey@redhat.com>

	* infcall.c (do_delete_breakpoint_by_number): New function.

	(call_function_by_hand): Refer to momentary breakpoint by number.

	* breakpoint.h (set_momentary_breakpoint_at_pc_with_number):

	Declare.

	* breakpoint.c (set_momentary_breakpoint_at_pc_with_number): New

	function.

Index: gdb-7.0.90.20100312/gdb/breakpoint.c

===================================================================

--- gdb-7.0.90.20100312.orig/gdb/breakpoint.c	2010-03-12 14:54:26.000000000 +0100

+++ gdb-7.0.90.20100312/gdb/breakpoint.c	2010-03-12 14:54:53.000000000 +0100

@@ -6115,6 +6115,20 @@ set_momentary_breakpoint_at_pc (struct g

   return set_momentary_breakpoint (gdbarch, sal, null_frame_id, type);

 }

+

+/* Like set_momentary_breakpoint_at_pc, but ensure that the new

+   breakpoint has a number.  */

+

+struct breakpoint *

+set_momentary_breakpoint_at_pc_with_number (struct gdbarch *gdbarch,

+					    CORE_ADDR pc,

+					    enum bptype type)

+{

+  struct breakpoint *result = set_momentary_breakpoint_at_pc (gdbarch, pc,

+							      type);

+  result->number = internal_breakpoint_number--;

+  return result;

+}

 /* Tell the user we have just set a breakpoint B.  */

Index: gdb-7.0.90.20100312/gdb/breakpoint.h

===================================================================

--- gdb-7.0.90.20100312.orig/gdb/breakpoint.h	2010-03-12 14:54:26.000000000 +0100

+++ gdb-7.0.90.20100312/gdb/breakpoint.h	2010-03-12 14:54:53.000000000 +0100

@@ -774,6 +774,9 @@ extern struct breakpoint *set_momentary_

 extern struct breakpoint *set_momentary_breakpoint_at_pc

   (struct gdbarch *, CORE_ADDR pc, enum bptype type);

+extern struct breakpoint *set_momentary_breakpoint_at_pc_with_number

+  (struct gdbarch *, CORE_ADDR pc, enum bptype type);

+

 extern struct breakpoint *clone_momentary_breakpoint (struct breakpoint *bpkt);

 extern void set_ignore_count (int, int, int);

Index: gdb-7.0.90.20100312/gdb/infcall.c

===================================================================

--- gdb-7.0.90.20100312.orig/gdb/infcall.c	2010-03-12 14:54:26.000000000 +0100

+++ gdb-7.0.90.20100312/gdb/infcall.c	2010-03-12 14:55:19.000000000 +0100

@@ -410,6 +410,18 @@ run_inferior_call (struct thread_info *c

   return e;

 }

+/* A cleanup function that deletes a breakpoint, if it still exists,

+   given the breakpoint's number.  */

+

+static void

+do_delete_breakpoint_by_number (void *arg)

+{

+  int *num = arg;

+  struct breakpoint *bp = get_breakpoint (*num);

+  if (bp)

+    delete_breakpoint (bp);

+}

+

 /* All this stuff with a dummy frame may seem unnecessarily complicated

    (why not just save registers in GDB?).  The purpose of pushing a dummy

    frame which looks just like a real frame is so that if you call a

@@ -447,7 +459,8 @@ call_function_by_hand (struct value *fun

   struct cleanup *args_cleanup;

   struct frame_info *frame;

   struct gdbarch *gdbarch;

-  struct breakpoint *terminate_bp = NULL;

+  int terminate_bp_num = 0;

+  CORE_ADDR terminate_bp_addr = 0;

   struct minimal_symbol *tm;

   struct cleanup *terminate_bp_cleanup = NULL;

   ptid_t call_thread_ptid;

@@ -765,8 +778,13 @@ call_function_by_hand (struct value *fun

        struct minimal_symbol *tm = lookup_minimal_symbol  ("std::terminate()",

 							   NULL, NULL);

        if (tm != NULL)

-	   terminate_bp = set_momentary_breakpoint_at_pc

+	 {

+	   struct breakpoint *bp;

+	   bp = set_momentary_breakpoint_at_pc_with_number

 	     (gdbarch, SYMBOL_VALUE_ADDRESS (tm),  bp_breakpoint);

+	   terminate_bp_num = bp->number;

+	   terminate_bp_addr = bp->loc->address;

+	 }

      }

   /* Everything's ready, push all the info needed to restore the

@@ -780,8 +798,9 @@ call_function_by_hand (struct value *fun

   discard_cleanups (inf_status_cleanup);

   /* Register a clean-up for unwind_on_terminating_exception_breakpoint.  */

-  if (terminate_bp)

-    terminate_bp_cleanup = make_cleanup_delete_breakpoint (terminate_bp);

+  if (terminate_bp_num != 0)

+    terminate_bp_cleanup = make_cleanup (do_delete_breakpoint_by_number,

+					 &terminate_bp_num);

   /* - SNIP - SNIP - SNIP - SNIP - SNIP - SNIP - SNIP - SNIP - SNIP -

      If you're looking to implement asynchronous dummy-frames, then

@@ -947,9 +966,9 @@ When the function is done executing, GDB

 		 in an inferior function call. Rewind, and warn the

 		 user.  */

-	      if (terminate_bp != NULL

+	      if (terminate_bp_num != 0

 		  && (inferior_thread ()->stop_bpstat->breakpoint_at->address

-		      == terminate_bp->loc->address))

+		      == terminate_bp_addr))

 		{

 		  /* We must get back to the frame we were before the

 		     dummy call.  */

@@ -998,7 +1017,7 @@ When the function is done executing, GDB

   /* If we get here and the std::terminate() breakpoint has been set,

      it has to be cleaned manually.  */

-  if (terminate_bp)

+  if (terminate_bp_num != 0)

     do_cleanups (terminate_bp_cleanup);

   /* If we get here the called FUNCTION ran to completion,