Re: [PATCH] [gdbserver] Disable conditional breakpoints on no-hardware-single-step targets

Antoine Tremblay
2015-05-08T12:12:52Z

On 05/08/2015 07:50 AM, Pedro Alves wrote:
> On 05/07/2015 12:45 PM, Antoine Tremblay wrote:
>
>> Just fyi, I'm working on doing this at the moment, my investigation is
>> still incomplete...
>>
>> So far I mainly plan to port the arm_get_next code to gdbserver, to
>> accomplish 1. , the code doesn't have so many deps so it should be ok
>> 2. by looking at $cpsr
>> 3. should be fine as 1 and 2 are done...
>>
>> I don't know however yet the best strategy to share the code but I'm
>> guessing I could make the parts that don't have any deps to gdbarch etc
>> in a shared function with gdb/gdbserver... Any pointers on this are
>> welcome...
>
> Yeah, sharing is good.
>
> Maybe adding an abstraction layer object, like:
>
> struct get_next_pc;
>
> struct get_next_pc_ops
> {
> void (*read_memory) (struct get_next_pc *self, ...);
> void (*read_register) (struct get_next_pc *self, ...);
> ...
> };
>
> struct get_next_pcs
> {
> struct get_next_pc_ops *vtable;
>
> VEC(CORE_ADDR) *result;
>
> enum bfd_endian byte_order;
> enum bfd_endian byte_order_for_code;
> whatever_type whatever_other_context;
> ...
> };
>
> And then both GDB and GDBserver would instantiate
> a struct get_next_pc object, like:
>
> struct get_next_pc_ops gdb_get_next_pc_ops = {
> gdb_get_next_pc_read_memory,
> gdb_get_next_pc_read_register,
> ...
> }
>
> struct gdb_get_next_pcs
> {
> struct get_next_pc base;
>
> // add whatever other context only gdb needs.
> };
>
> int
> arm_software_single_step (struct frame_info *frame)
> {
> struct gdbarch *gdbarch = get_frame_arch (frame);
> struct gdb_get_next_pc next_pc;
> CORE_ADDR pc;
>
> next_pc.vtable = gdb_get_next_pc_ops;
> next_pc.byte_order = gdbarch_byte_order (gdbarch);
> next_pc.byte_order_for_code = gdbarch_byte_order_for_code (gdbarch);
>
> // arm_get_next_pcs is the existing gdb code adjusted to the
> // new interface.
> arm_get_next_pcs (&next_pc);
>
> // walk result vec (a VEC of CORE_ADDRs) and insert breakpoints.
> // alternatively add a insert_breakpoint callback to struct get_next_pc_ops
> // and insert breakpoints from within arm_get_next_pcs, as currently.
> for (i = 0;
> VEC_iterate (CORE_ADDR, next_pcs.result, i, pc);
> ++i)
> {
> arm_insert_single_step_breakpoint (gdbarch, aspace, pc);
> }
>
> return 1;
> }
>

This looks very nice thanks! , but I do have one question , why is the
result a VEC ?

From the context and current code won't we have only one next instruction ?

Also, if you may,file structure wise, where would be a good place for
this abstration layer in your view ?

Thanks,
Antoine