Re: [Qemu-devel] [PATCH RFC v20 3/8] target/avr: Add mechanism to check for active debugger connection

[Michael Rolnik]

1. There's a break instruction
https://www.microchip.com/webdoc/avrassembler/avrassembler.wb_BREAK.html
2. There's a set of tests that use break.

So I assume I have to implement this instruction as described in the spec.

Sent from my cell phone, please ignore typos

On Mon, Jun 3, 2019, 6:44 PM Richard Henderson <address@hidden>
wrote:

> On 6/1/19 4:12 PM, Michael Rolnik wrote:
> > Hi Richard.
> >
> > If I implement it this way
> >
> > ```
> >  static bool trans_BREAK(DisasContext *ctx, arg_BREAK *a)
> >  {
> >      if (avr_feature(ctx->env, AVR_FEATURE_BREAK) == false) {
> >          gen_helper_unsupported(cpu_env);
> >      } else {
> >          tcg_gen_movi_tl(cpu_pc, ctx->inst[0].npc);
> >          gen_helper_debug(cpu_env);
> >      }
> >
> >      ctx->bstate = BS_EXCP;
> >
> >      return true;
> >  }
> > ```
> >
> > qemu (without -s -S flags) crashes when debugger is not connected
>
> I was not suggesting using the internal qemu EXCP_DEBUG, but another AVR
> specific exception, much the same way as every other cpu has a cpu-specific
> debug exception.
>
> Or perhaps always do nothing.  Why is gdb insertting BREAK in the first
> place?
>  It should be using the "hardware breakpoint" support that qemu advertises
> as
> part of the gdbstub protocol, and that you support here:
>
> > +        if (unlikely(cpu_breakpoint_test(cs, OFFSET_CODE + cpc * 2,
> BP_ANY))
> > +                 || cpu_breakpoint_test(cs, OFFSET_DATA + cpc * 2,
> BP_ANY)) {
> > +            tcg_gen_movi_i32(cpu_pc, cpc);
> > +            gen_helper_debug(cpu_env);
> > +            ctx.bstate = BS_EXCP;
> > +            goto done_generating;
> > +        }
>
>
>
> r~
>