Re: GDB remote protocol and conditional breakpoints

On 09/10/2015 11:42 PM, Luis Machado wrote:
> On 09/10/2015 06:22 PM, David Taylor wrote:
>> In GDB's remote protocol, there is a Z0 command for setting breakpoints.
>> The summary of the Z0 command is:
>>
>>      Z0,addr,kind[;cond_list...][;cmds:persist,cmd_list...]
>>
>> I have a question about the cond_list part.  The description in the
>> manual says, in part:
>>
>>      cond_list is an optional list of conditional expressions in bytecode
>>      form that should be evaluated on the target's side.  These are
>>      conditions that should be taken into consideration when deciding if
>>      the breakpoint trigger should be reported back to GDBN.
>>
>>      The cond_list parameter is comprised of a series of expressions,
>>      concatenated without separators.
>>
>> If there is only one expression, no problem.  But, if there are multiple
>> expressions, should the stub treat them as having an implicit || between
>> them?  Or an implicit && ?  Or something else?
>>
>> That is, is the breakpoint reported to GDB and the commands run if *ANY*
>> of the conditions are true?  If *ALL* of the conditions are true?  Or
>> something else?
>>
>> What is the intent when there are multiple conditions?
> 
> I remember implementing this first as an implicit &&, but then we ended 
> up changing it to ||, as evidenced by the comment in the code in 
> mem-break.c:gdb_condition_true_at_breakpoint_z_type:

Yeah, that's because each of the conditions comes from separate
breakpoint on the GDB side.  E.g, if you have:

 (gdb) break foo if global == 1
 (gdb) break foo if global == 2

When the breakpoint at foo hits, the stop should be reported
to the user if global == 1 OR global == 2.

Thanks,
Pedro Alves