"catch catch/throw/rethrow", breakpoint -> catchpoint
authorPedro Alves <palves@redhat.com>
Tue, 9 Jul 2019 18:26:16 +0000 (19:26 +0100)
committerPedro Alves <palves@redhat.com>
Tue, 9 Jul 2019 18:34:18 +0000 (19:34 +0100)
commitcb1e4e32c2d9588e1d77ea49bafb5dcdc1cff764
tree3c878afb8e0496bb08632c5fbcb50e9f167554e6
parentb58a68fe5709ed205c3ac54065f1783ce58d9a01
"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"'.
12 files changed:
gdb/ChangeLog
gdb/break-catch-throw.c
gdb/breakpoint.c
gdb/breakpoint.h
gdb/doc/ChangeLog
gdb/doc/gdb.texinfo
gdb/python/py-breakpoint.c
gdb/testsuite/ChangeLog
gdb/testsuite/gdb.cp/except-multi-location.exp
gdb/testsuite/gdb.cp/exception.exp
gdb/testsuite/gdb.mi/mi-catch-cpp-exceptions.exp
gdb/testsuite/gdb.python/py-breakpoint.exp