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

[liweiwei]

On 2023/4/3 16:09, Philippe Mathieu-Daudé wrote:
> On 1/4/23 06:51, Richard Henderson wrote:
> > From: Weiwei Li <liweiwei@iscas.ac.cn>
> >
> > CPUs often set CF_PCREL in tcg_cflags before qemu_init_vcpu(), in which
> > tcg_cflags will be overwrited by tcg_cpu_init_cflags().
>
> The description makes sense, but I couldn't reproduce using:
>
> -- >8 --
> diff --git a/accel/tcg/tcg-accel-ops.c b/accel/tcg/tcg-accel-ops.c
> index af35e0d092..23ebf7de21 100644
> --- a/accel/tcg/tcg-accel-ops.c
> +++ b/accel/tcg/tcg-accel-ops.c
> @@ -59,6 +59,7 @@ void tcg_cpu_init_cflags(CPUState *cpu, bool parallel)
>
>      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.

Regards,

Weiwei Li


> > Fixes: 4be790263ffc ("accel/tcg: Replace `TARGET_TB_PCREL` with 
> > `CF_PCREL`")
> > Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> > Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
> > Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
> > Message-Id: <20230331150609.114401-6-liweiwei@iscas.ac.cn>
> > Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> > ---
> >   accel/tcg/tcg-accel-ops.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > 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.
>
> >   }
> >     void tcg_cpus_destroy(CPUState *cpu)