Re: [PATCH 2/3] accel/tcg: Fix overwrite problems of tcg_cflags

[Anton Johansson]

On 4/3/23 11:09, liweiwei wrote:
> On 2023/4/3 16:09, Philippe Mathieu-Daudé wrote:
> >      cflags |= parallel ? CF_PARALLEL : 0;
> >      cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
> > +    tcg_debug_assert(!cpu->tcg_cflags);
> >      cpu->tcg_cflags = cflags;
> >  }
> > ---
> >
> > Li and Junqiang, what is your use case?
>
> Only few CPUs support CF_PCREL currently. I found this problem when I 
> tried to introduce PC-relative translation into RISC-V.
>
> Maybe It also can be reproduced in system mode for ARM and X86.

Yes, this can be reproduced on arm-softmmu with --enable-debug-tcg and 
the above assertion.


On 4/3/23 10:09, Philippe Mathieu-Daudé wrote:
> > diff --git a/accel/tcg/tcg-accel-ops.c b/accel/tcg/tcg-accel-ops.c
> > index af35e0d092..58c8e64096 100644
> > --- a/accel/tcg/tcg-accel-ops.c
> > +++ b/accel/tcg/tcg-accel-ops.c
> > @@ -59,7 +59,7 @@ void tcg_cpu_init_cflags(CPUState *cpu, bool parallel)
> >         cflags |= parallel ? CF_PARALLEL : 0;
> >       cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
> > -    cpu->tcg_cflags = cflags;
> > +    cpu->tcg_cflags |= cflags;
>
> This could be acceptable as a release kludge, but semantically
> tcg_cpu_init_cflags() is meant to *initialize* all flags, not
> set few of them. Either we aren't calling it from the proper place,
> or we need to rename it.
Agree, this sounds reasonable.  Also, maybe setting
cpu->tcg_cflags from *_cpu_realizefn was not the right call and
we should have some other way of providing target specific cflags.

--
Anton Johansson,
rev.ng Labs Srl.