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Re: [PATCH 2/2] "catch catch/throw/rethrow", breakpoint -> catchpoint
* Pedro Alves <palves@redhat.com> [2019-07-05 17:00:55 +0100]:
> 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
>
I agree for users knowing the address is probably not helpful, but we
also have 'maintenance info breakpoints'. I think it might (one day)
be helpful if we _did_ print the address in the maintenance version of
the command.
thanks,
Andrew
> 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:
> yyyy-mm-dd 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/testsuite/ChangeLog:
> yyyy-mm-dd 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/break-catch-throw.c | 25 +++---
> gdb/breakpoint.c | 108 +++++++++++++------------
> gdb/breakpoint.h | 7 +-
> gdb/python/py-breakpoint.c | 8 +-
> gdb/testsuite/gdb.cp/except-multi-location.exp | 6 +-
> gdb/testsuite/gdb.cp/exception.exp | 18 +----
> gdb/testsuite/gdb.python/py-breakpoint.exp | 5 +-
> 7 files changed, 84 insertions(+), 93 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
> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
> index d508921fdc5..36500758257 100644
> --- a/gdb/breakpoint.c
> +++ b/gdb/breakpoint.c
> @@ -5603,8 +5603,10 @@ bpstat_what (bpstat bs_head)
> }
> else
> {
> - /* There was a catchpoint, but we're not stopping.
> - This requires no further action. */
> + /* Some catchpoints are implemented with breakpoints.
> + For those, we need to step over the breakpoint. */
> + if (bs->bp_location_at->loc_type != bp_loc_other)
> + this_action = BPSTAT_WHAT_SINGLE;
> }
> break;
> case bp_jit_event:
> @@ -6686,27 +6688,21 @@ describe_other_breakpoints (struct gdbarch *gdbarch,
> }
>
>
> -/* Return true iff it is meaningful to use the address member of
> - BPT locations. For some breakpoint types, the locations' address members
> - are irrelevant and it makes no sense to attempt to compare them to other
> - addresses (or use them for any other purpose either).
> -
> - More specifically, each of the following breakpoint types will
> - always have a zero valued location address and we don't want to mark
> - breakpoints of any of these types to be a duplicate of an actual
> - breakpoint location at address zero:
> -
> - bp_watchpoint
> - bp_catchpoint
> +/* Return true iff it is meaningful to use the address member of LOC.
> + For some breakpoint types, the locations' address members are
> + irrelevant and it makes no sense to attempt to compare them to
> + other addresses (or use them for any other purpose either).
>
> -*/
> + More specifically, software watchpoints and catchpoints that are
> + not backed by breakpoints always have a zero valued location
> + address and we don't want to mark breakpoints of any of these types
> + to be a duplicate of an actual breakpoint location at address
> + zero. */
>
> -static int
> -breakpoint_address_is_meaningful (struct breakpoint *bpt)
> +static bool
> +bl_address_is_meaningful (bp_location *loc)
> {
> - enum bptype type = bpt->type;
> -
> - return (type != bp_watchpoint && type != bp_catchpoint);
> + return loc->loc_type != bp_loc_other;
> }
>
> /* Assuming LOC1 and LOC2's owners are hardware watchpoints, returns
> @@ -6838,8 +6834,8 @@ tracepoint_locations_match (struct bp_location *loc1,
> }
>
> /* Assuming LOC1 and LOC2's types' have meaningful target addresses
> - (breakpoint_address_is_meaningful), returns true if LOC1 and LOC2
> - represent the same location. */
> + (bl_address_is_meaningful), returns true if LOC1 and LOC2 represent
> + the same location. */
>
> static int
> breakpoint_locations_match (struct bp_location *loc1,
> @@ -6937,16 +6933,10 @@ adjust_breakpoint_address (struct gdbarch *gdbarch,
> }
> }
>
> -bp_location::bp_location (breakpoint *owner)
> +static bp_loc_type
> +bp_location_from_bp_type (bptype type)
> {
> - bp_location *loc = this;
> -
> - loc->owner = owner;
> - loc->cond_bytecode = NULL;
> - loc->shlib_disabled = 0;
> - loc->enabled = 1;
> -
> - switch (owner->type)
> + switch (type)
> {
> case bp_breakpoint:
> case bp_single_step:
> @@ -6972,30 +6962,44 @@ bp_location::bp_location (breakpoint *owner)
> case bp_gnu_ifunc_resolver:
> case bp_gnu_ifunc_resolver_return:
> case bp_dprintf:
> - loc->loc_type = bp_loc_software_breakpoint;
> - mark_breakpoint_location_modified (loc);
> - break;
> + return bp_loc_software_breakpoint;
> case bp_hardware_breakpoint:
> - loc->loc_type = bp_loc_hardware_breakpoint;
> - mark_breakpoint_location_modified (loc);
> - break;
> + return bp_loc_hardware_breakpoint;
> case bp_hardware_watchpoint:
> case bp_read_watchpoint:
> case bp_access_watchpoint:
> - loc->loc_type = bp_loc_hardware_watchpoint;
> - break;
> + return bp_loc_hardware_watchpoint;
> case bp_watchpoint:
> case bp_catchpoint:
> case bp_tracepoint:
> case bp_fast_tracepoint:
> case bp_static_tracepoint:
> - loc->loc_type = bp_loc_other;
> - break;
> + return bp_loc_other;
> default:
> internal_error (__FILE__, __LINE__, _("unknown breakpoint type"));
> }
> +}
> +
> +bp_location::bp_location (breakpoint *owner, bp_loc_type type)
> +{
> + this->owner = owner;
> + this->cond_bytecode = NULL;
> + this->shlib_disabled = 0;
> + this->enabled = 1;
> +
> + this->loc_type = type;
>
> - loc->refc = 1;
> + if (this->loc_type == bp_loc_software_breakpoint
> + || this->loc_type == bp_loc_hardware_breakpoint)
> + mark_breakpoint_location_modified (this);
> +
> + this->refc = 1;
> +}
> +
> +bp_location::bp_location (breakpoint *owner)
> + : bp_location::bp_location (owner,
> + bp_location_from_bp_type (owner->type))
> +{
> }
>
> /* Allocate a struct bp_location. */
> @@ -8643,11 +8647,12 @@ bp_loc_is_permanent (struct bp_location *loc)
> {
> gdb_assert (loc != NULL);
>
> - /* If we have a catchpoint or a watchpoint, just return 0. We should not
> - attempt to read from the addresses the locations of these breakpoint types
> - point to. program_breakpoint_here_p, below, will attempt to read
> + /* If we have a non-breakpoint-backed catchpoint or a software
> + watchpoint, just return 0. We should not attempt to read from
> + the addresses the locations of these breakpoint types point to.
> + program_breakpoint_here_p, below, will attempt to read
> memory. */
> - if (!breakpoint_address_is_meaningful (loc->owner))
> + if (!bl_address_is_meaningful (loc))
> return 0;
>
> scoped_restore_current_pspace_and_thread restore_pspace_thread;
> @@ -11455,10 +11460,9 @@ breakpoint_auto_delete (bpstat bs)
>
> /* A comparison function for bp_location AP and BP being interfaced to
> qsort. Sort elements primarily by their ADDRESS (no matter what
> - does breakpoint_address_is_meaningful say for its OWNER),
> - secondarily by ordering first permanent elements and
> - terciarily just ensuring the array is sorted stable way despite
> - qsort being an unstable algorithm. */
> + bl_address_is_meaningful says), secondarily by ordering first
> + permanent elements and terciarily just ensuring the array is sorted
> + stable way despite qsort being an unstable algorithm. */
>
> static int
> bp_locations_compare (const void *ap, const void *bp)
> @@ -11798,7 +11802,7 @@ update_global_location_list (enum ugll_insert_mode insert_mode)
> this one from the target. */
>
> /* OLD_LOC comes from existing struct breakpoint. */
> - if (breakpoint_address_is_meaningful (old_loc->owner))
> + if (bl_address_is_meaningful (old_loc))
> {
> for (loc2p = locp;
> (loc2p < bp_locations + bp_locations_count
> @@ -11938,7 +11942,7 @@ update_global_location_list (enum ugll_insert_mode insert_mode)
> b = loc->owner;
>
> if (!unduplicated_should_be_inserted (loc)
> - || !breakpoint_address_is_meaningful (b)
> + || !bl_address_is_meaningful (loc)
> /* Don't detect duplicate for tracepoint locations because they are
> never duplicated. See the comments in field `duplicate' of
> `struct bp_location'. */
> diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
> index 75f19785cb1..6e9a35e82de 100644
> --- a/gdb/breakpoint.h
> +++ b/gdb/breakpoint.h
> @@ -316,7 +316,12 @@ class bp_location
> public:
> bp_location () = default;
>
> - bp_location (breakpoint *owner);
> + /* Construct a bp_location with the type inferred from OWNER's
> + type. */
> + explicit bp_location (breakpoint *owner);
> +
> + /* Construct a bp_location with type TYPE. */
> + bp_location (breakpoint *owner, bp_loc_type type);
>
> virtual ~bp_location ();
>
> diff --git a/gdb/python/py-breakpoint.c b/gdb/python/py-breakpoint.c
> index 88cd7de3343..698d91e9d32 100644
> --- a/gdb/python/py-breakpoint.c
> +++ b/gdb/python/py-breakpoint.c
> @@ -379,7 +379,6 @@ bppy_set_hit_count (PyObject *self, PyObject *newvalue, void *closure)
> static PyObject *
> bppy_get_location (PyObject *self, void *closure)
> {
> - const char *str;
> gdbpy_breakpoint_object *obj = (gdbpy_breakpoint_object *) self;
>
> BPPY_REQUIRE_VALID (obj);
> @@ -387,12 +386,7 @@ bppy_get_location (PyObject *self, void *closure)
> if (obj->bp->type != bp_breakpoint)
> Py_RETURN_NONE;
>
> - struct event_location *location = obj->bp->location.get ();
> - /* "catch throw" makes a breakpoint of type bp_breakpoint that does
> - not have a location. */
> - if (location == nullptr)
> - Py_RETURN_NONE;
> - str = event_location_to_string (location);
> + const char *str = event_location_to_string (obj->bp->location.get ());
> if (! str)
> str = "";
> return host_string_to_python_string (str).release ();
> diff --git a/gdb/testsuite/gdb.cp/except-multi-location.exp b/gdb/testsuite/gdb.cp/except-multi-location.exp
> index 60d6d0b9351..1258d893afb 100644
> --- a/gdb/testsuite/gdb.cp/except-multi-location.exp
> +++ b/gdb/testsuite/gdb.cp/except-multi-location.exp
> @@ -74,9 +74,9 @@ proc test_multi_libstdcpp {static_bin static_lib} {
> set ws "\[ \t\]*"
> gdb_test "info breakpoints" \
> [multi_line \
> - "${decimal}${ws}breakpoint${ws}keep${ws}y${ws}${hex}${ws}exception catch" \
> - "${decimal}${ws}breakpoint${ws}keep${ws}y${ws}${hex}${ws}exception throw" \
> - "${decimal}${ws}breakpoint${ws}keep${ws}y${ws}${hex}${ws}exception rethrow"]
> + "${decimal}${ws}catchpoint${ws}keep${ws}y${ws}exception catch" \
> + "${decimal}${ws}catchpoint${ws}keep${ws}y${ws}exception throw" \
> + "${decimal}${ws}catchpoint${ws}keep${ws}y${ws}exception rethrow"]
> }
>
> # Try different static/not-static combinations.
> diff --git a/gdb/testsuite/gdb.cp/exception.exp b/gdb/testsuite/gdb.cp/exception.exp
> index 4761de20e19..0be382ba98c 100644
> --- a/gdb/testsuite/gdb.cp/exception.exp
> +++ b/gdb/testsuite/gdb.cp/exception.exp
> @@ -62,16 +62,10 @@ gdb_test "catch rethrow" "Catchpoint \[0-9\]+ \\(rethrow\\)" \
> "catch rethrow (before inferior run)"
>
>
> -# The catchpoints should be listed in the list of breakpoints.
> -# In case of a statically linked test, we won't have a pending breakpoint.
> -# Hence we allow for both an address or "<PENDING>". If we ever become able
> -# to tell whether the target is linked statically or not, we can be more
> -# precise and require exact output.
> -set addr "\(<PENDING>|$hex\)"
> set re_head "Num${ws}Type${ws}Disp${ws}Enb${ws}Address${ws}What"
> -set re_2_bp "1${ws}breakpoint${ws}keep${ws}y${ws}$addr${ws}exception catch"
> -set re_3_bp "2${ws}breakpoint${ws}keep${ws}y${ws}$addr${ws}exception throw"
> -set re_4_bp "3${ws}breakpoint${ws}keep${ws}y${ws}$addr${ws}exception rethrow"
> +set re_2_bp "1${ws}catchpoint${ws}keep${ws}y${ws}exception catch"
> +set re_3_bp "2${ws}catchpoint${ws}keep${ws}y${ws}exception throw"
> +set re_4_bp "3${ws}catchpoint${ws}keep${ws}y${ws}exception rethrow"
>
> set name "info breakpoints (before inferior run)"
> gdb_test_multiple "info breakpoints" $name {
> @@ -100,12 +94,6 @@ if { !$ok } {
> continue
> }
>
> -set addr "$hex"
> -set re_head "Num${ws}Type${ws}Disp${ws}Enb${ws}Address${ws}What"
> -set re_2_bp "1${ws}breakpoint${ws}keep${ws}y${ws}$addr${ws}exception catch"
> -set re_3_bp "2${ws}breakpoint${ws}keep${ws}y${ws}$addr${ws}exception throw"
> -set re_4_bp "3${ws}breakpoint${ws}keep${ws}y${ws}$addr${ws}exception rethrow"
> -
> set name "info breakpoints (after inferior run)"
> gdb_test_multiple "info breakpoints" $name {
> -re "$re_head${ws}$re_2_bp${ws}$re_3_bp${ws}$re_4_bp\r\n$gdb_prompt $" {
> diff --git a/gdb/testsuite/gdb.python/py-breakpoint.exp b/gdb/testsuite/gdb.python/py-breakpoint.exp
> index 241e7e6839e..625977c0ad4 100644
> --- a/gdb/testsuite/gdb.python/py-breakpoint.exp
> +++ b/gdb/testsuite/gdb.python/py-breakpoint.exp
> @@ -619,8 +619,9 @@ proc_with_prefix test_bkpt_explicit_loc {} {
>
> delete_breakpoints
> gdb_test "catch throw" "Catchpoint .* \\(throw\\)"
> - gdb_test "python print (gdb.breakpoints()\[0\].location)" None \
> - "Examine location of catchpoint"
> + gdb_test "python print (gdb.breakpoints())" \
> + "\(\)" \
> + "catch throw is not a breakpoint"
> }
>
> proc_with_prefix test_bkpt_qualified {} {
> --
> 2.14.5
>