Re: [PATCH 2/2] new tracepoint downloaded MI notification.

Yao Qi
2012-09-29T14:13:07Z

On 09/29/2012 01:46 AM, Pedro Alves wrote:
>> Took me a second to recall, but the reason the address is
>> >necessary is multi-location tracepoints -- a tracepoint on the
>> >target is identified by the { number, address } tuple. We don't
>> >send over the location's sub number (like 1.1, 1.2, etc.).
>> >
>> >Should we mention this somewhere (other than at the tracepoint
>> >packets description), so frontend people don't wonder whether they
>> >can ignore the address field, and why aren't the other fields of
>> >the tracepoint (like spec string) included?
> And I guess the related question is, are frontends interested
> in { number, address }, which is target side detail, or on
> { number, location number }, which is how other breakpoints are
> presented to the frontend? I would think the latter?

From the frontend's point of view, {number, location number} is better,
and the schema "number.location_number" has been used in
"=breakpoint-modified" notification. However, if we want to use
{number, location number} here, we have to guarantee that the location
number is an attribute of bp_location, because:

Nowadays, location number is generated by incrementing a counter during
iterating a list of bp_location of breakpoint (in
breakpoint.c:print_one_breakpoint), so I am wondering that the
bp_location object may have the different number, if the list of
bp_locations of a breakpoint is removed due to some reasons. Looks
bp_location list of breakpoint is *not* removed except in
breakpoint_program_space_exit, after examine the source code.

For example,

Originally we have a tracepoint of 3 locations,

4 tracepoint keep y <MULTIPLE>
collect $eip^M
4.1 y 0x0804859c in func4 inf 1
4.2 y 0xb7ffc480 in func4 inf 2
4.3 y 0xb7ffc488 in func4 inf 1

due to some reason, bp_location on address 0xb7ffc480 is removed (for
example, inferior 2 is removed), and original bp_location 4.3 becomes 4.2.

In short, if we can make location number persistent (unchanged for a
given bp_location object), then {number, location number} is fine,
otherwise, I'd prefer {number, address}.

--
Yao