Re: [RFA/7.8] user breakpoint not inserted if software-single-step at same location

Pedro Alves
2014-06-03T15:41:00Z

On 06/03/2014 02:35 PM, Joel Brobecker wrote:
> Hi Pedro,
>
>>> Bah, I woke up realizing that the version I posted forgets to
>>> clone the shadow buffer! Let me fix that and repost...
>
> You are producing patches so fast, I am wondering if I will be able
> to keep up! :-)

:-)

>> @@ -15138,12 +15196,30 @@ deprecated_insert_raw_breakpoint (struct gdbarch *gdbarch,
>> struct address_space *aspace, CORE_ADDR pc)
>> {
>> struct bp_target_info *bp_tgt;
>> + struct bp_location *bl;
>>
>> bp_tgt = XCNEW (struct bp_target_info);
>>
>> bp_tgt->placed_address_space = aspace;
>> bp_tgt->placed_address = pc;
>>
>> + /* If an unconditional non-raw breakpoint is already inserted at
>> + that location, there's no need to insert another. However, with
>> + target-side evaluation of breakpoint conditions, if the
>> + breakpoint that is currently inserted on the target is
>> + conditional, we need to make it unconditional. Note that a
>> + breakpoint with target-side commands is not reported even if
>> + unconditional, so we need to remove the commands from the target
>> + as well. */
>> + bl = find_non_raw_software_breakpoint_inserted_here (aspace, pc);
>> + if (bl != NULL
>> + && VEC_empty (agent_expr_p, bl->target_info.conditions)
>> + && VEC_empty (agent_expr_p, bl->target_info.tcommands))
>> + {
>> + bp_target_info_copy_insertion_state (bp_tgt, &bl->target_info);
>> + return bp_tgt;
>> + }
>> +
>
> ISTM that you are assuming that there would only be one other breakpoint
> inserted at this location. What if there were more?

Yep, it's a valid assumption. Only one of those can be the one that
is actually inserted in the target. All others breakpoints are considered
duplicates, with bl->duplicate == 1 and bl->inserted == 0, and never reach
the target. The duplicate location logic in the tail of update_global_location_list
takes care of it:

/* This and the above ensure the invariant that the first location
is not duplicated, and is the inserted one.
All following are marked as duplicated, and are not inserted. */
if (loc->inserted)
swap_insertion (loc, *loc_first_p);
loc->duplicate = 1;

The one that is inserted will hold a merge of all the agent
expressions (in target_info.conditions and target_info.tcommands) of
the target-side conditions and commands of all breakpoints at that
address. Those are computed just before that single breakpoint
is inserted (build_target_condition_list, build_target_command_list).

--
Pedro Alves