"catch catch/throw/rethrow", breakpoint -> catchpoint

Currently, with:

 (gdb) catch catch
 Catchpoint 1 (catch)
 (gdb) catch throw
 Catchpoint 2 (throw)
 (gdb) catch rethrow
 Catchpoint 3 (rethrow)

You get:

(gdb) info breakpoints
 Num     Type           Disp Enb Address            What
 1       breakpoint     keep y   0x0000000000b122af exception catch
 2       breakpoint     keep y   0x0000000000b1288d exception throw
 3       breakpoint     keep y   0x0000000000b12931 exception rethrow

I think it doesn't make much sense usability-wise, to show a
catchpoint as a breakpoint.  The fact that GDB sets a breakpoint at
some magic address in the C++ run time is an implementation detail,
IMO.  And as seen in the previous patch, such a catchpoint can end up
with more than one location/address even, so showing a single address
isn't entirely accurate.

This commit hides the addresses from view, and makes GDB show
"catchpoint" for type as well:

  (gdb) info breakpoints
  Num     Type           Disp Enb Address            What
  1       catchpoint     keep y                      exception catch
  2       catchpoint     keep y                      exception throw
  3       catchpoint     keep y                      exception rethrow

This comment in the code seems telling:

  /* We need to reset 'type' in order for code in breakpoint.c to do
     the right thing.  */
  cp->type = bp_breakpoint;

It kind of suggests that the reason catchpoints end up shown as
breakpoints was that it was easier to implement them that way, rather
than a desired property.

This commit fixes things up to make it possible to have bp_catch
breakpoints have software/hardware breakpoint locations, thus
eliminating the need for that hack:

 - redo breakpoint_address_is_meaningful in terms of the location's
   type rather than breakpoint type.
 - teach bpstat_what about stepping over the catchpoint locations.
 - install a allocate_location method for "catch catch/throw/rethrow",
   one that forces the location type.

Note that this also reverts the gdb hunk from:

  commit 2a8be20359dba9cc684fd3ffa222d985399f3b18
  Commit:     Tom Tromey <tom@tromey.com>
  CommitDate: Sat Oct 6 22:17:45 2018 -0600

      Fix Python gdb.Breakpoint.location crash

because now "catch throw" catchpoints hit the

   if (obj->bp->type != bp_breakpoint)
     Py_RETURN_NONE;

check above, and, adjusts the testcase to no longer expect to see the
catchpoint in the gdb.breakpoints() list.

(Note: might make sense to do the same to Ada exception catchpoints.)

gdb/ChangeLog:
2019-07-09  Pedro Alves  <palves@redhat.com>

	* break-catch-throw.c (print_one_exception_catchpoint): Skip the
	"addr" field.
	(allocate_location_exception_catchpoint): New.
	(handle_gnu_v3_exceptions): Don't reset 'type' to bp_breakpoint.
	(initialize_throw_catchpoint_ops): Install
	allocate_location_exception_catchpoint as allocate_location
	method.
	* breakpoint.c (bpstat_what) <bp_catch>: Set action to
	BPSTAT_WHAT_SINGLE if not stopping and the location's type is not
	bp_loc_other.
	(breakpoint_address_is_meaningful): Delete.
	(bl_address_is_meaningful): New.
	(breakpoint_locations_match): Adjust comment.
	(bp_location_from_bp_type): New, factored out of...
	(bp_location::bp_location(breakpoint *)): ... this.
	(bp_location::bp_location(breakpoint *, bp_loc_type)): New,
	factored out of...
	(bp_location::bp_location(breakpoint *)): ... this.  Reimplement.
	(bp_loc_is_permanent): Use bl_address_is_meaningful instead of
	breakpoint_address_is_meaningful.
	(bp_locations_compare): Adjust comment.
	(update_global_location_list): Use bl_address_is_meaningful
	instead of breakpoint_address_is_meaningful.
	* breakpoint.h (bp_location::bp_location(breakpoint *)): New
	explicit.
	(bp_location::bp_location(breakpoint *, bp_loc_type)): Declare.
	* python/py-breakpoint.c (bppy_get_location): No longer check
	whether location is null.

gdb/doc/ChangeLog:
2019-07-09  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (C++ Exception GDB/MI Catchpoint Commands): Adjust
	examples to show type=catchpoint instead of type=breakpoint and an
	address.

gdb/testsuite/ChangeLog:
2019-07-09  Pedro Alves  <palves@redhat.com>

	* gdb.cp/catch-multi-stdlib.exp: Adjust expected "info
	breakpoints" output.
	* gdb.cp/exception.exp: Adjust expected "info breakpoints" output.
	* gdb.python/py-breakpoint.exp: No longer expect that "catch
	throw" creates breakpoint.
	* gdb.mi/mi-catch-cpp-exceptions.exp (setup_catchpoint): Expect
	'type="catchpoint"'.

1 files changed, 12 insertions, 13 deletions

diff --git a/gdb/break-catch-throw.c b/gdb/break-catch-throw.c
index 107ac74f5cc..c0b3eec63d1 100644
--- a/gdb/break-catch-throw.c
+++ b/gdb/break-catch-throw.c
@@ -249,18 +249,10 @@ print_one_exception_catchpoint (struct breakpoint *b,
   enum exception_event_kind kind = classify_exception_breakpoint (b);
 
   get_user_print_options (&opts);
+
   if (opts.addressprint)
-    {
-      annotate_field (4);
-      if (b->loc == NULL || b->loc->shlib_disabled)
-	uiout->field_string ("addr", "<PENDING>");
-      else
-	uiout->field_core_addr ("addr",
-				b->loc->gdbarch, b->loc->address);
-    }
+    uiout->field_skip ("addr");
   annotate_field (5);
-  if (b->loc)
-    *last_loc = b->loc;
 
   switch (kind)
     {
@@ -344,6 +336,15 @@ print_recreate_exception_catchpoint (struct breakpoint *b,
   print_recreate_thread (b, fp);
 }
 
+/* Implement the "allocate_location" breakpoint_ops method for throw
+   and catch catchpoints.  */
+
+static bp_location *
+allocate_location_exception_catchpoint (breakpoint *self)
+{
+  return new bp_location (self, bp_loc_software_breakpoint);
+}
+
 static void
 handle_gnu_v3_exceptions (int tempflag, std::string &&except_rx,
 			  const char *cond_string,
@@ -361,9 +362,6 @@ handle_gnu_v3_exceptions (int tempflag, std::string &&except_rx,
 
   init_catchpoint (cp.get (), get_current_arch (), tempflag, cond_string,
 		   &gnu_v3_exception_catchpoint_ops);
-  /* We need to reset 'type' in order for code in breakpoint.c to do
-     the right thing.  */
-  cp->type = bp_breakpoint;
   cp->kind = ex_event;
   cp->exception_rx = std::move (except_rx);
   cp->pattern = std::move (pattern);
@@ -521,6 +519,7 @@ initialize_throw_catchpoint_ops (void)
   ops->print_recreate = print_recreate_exception_catchpoint;
   ops->print_one_detail = print_one_detail_exception_catchpoint;
   ops->check_status = check_status_exception_catchpoint;
+  ops->allocate_location = allocate_location_exception_catchpoint;
 }
 
 void