Re: [Qemu-devel] [RFC PATCH v4 5/5] target/ppc: support single stepping with KVM HV

[Alexey Kardashevskiy]

On 13/06/2019 12:01, Fabiano Rosas wrote:
> Alexey Kardashevskiy <address@hidden> writes:
> 
>> It is TCG, a single CPU with a single thread and no matter where I put
> 
> Ok, but then none of this code gets executed because it is kvm-only:


I was not clear, this is a generic issue, not related to your patchset,
I just thought since you are looking at this already, you might find the
answer faster, that's it :)


> 
> qemu/exec.c
> void cpu_single_step(CPUState *cpu, int enabled)
> {
>     if (cpu->singlestep_enabled != enabled) {
>         cpu->singlestep_enabled = enabled;
>         if (kvm_enabled()) {
> ->           kvm_set_singlestep(cpu, enabled);
>         } else {
>             /* must flush all the translated code to avoid inconsistencies */
>             /* XXX: only flush what is necessary */
>             tb_flush(cpu);
>         }
>     }
> }
> 
>> this "stdu    r1,-368(r1)" - GDB does not stop on the next one and just
>> runs.
>>
>> In the example above:
>> 1. "b *0x10f16bc" makes GDB stop there, "ni" continues without stopping
>> on at 0x10f16c0.
> 
> But this seems wrong anyway. Let me try to reproduce it and see what I
> can find.


Thanks!

> 
>> 2. "b *0x10f16bc" and "b *0x10f16c0" make GDB stop at 0x10f16bc and "ni"
>> steps to 0x10f16c0 but it is rather because it is a breakpoint and not
>> the next instruction.
>> 3. "b *0x10f16bc" and "b *0x10f16c4" make GDB stop at 0x10f16bc and "ni"
>> stops GDB at 0x10f16bc but again it is a breakpoint.
>>
>> In 2 and 3 it is possible to continue step debugging till the next "stdu".
>>
> 

-- 
Alexey