Re: [PATCH] target/ppc: Integrate icount to purr, vtb, and tbu40

[Peter Maydell]

On Tue, 11 Aug 2020 at 02:29, Gustavo Romero <gromero@linux.ibm.com> wrote:
>
> Currently if option '-icount auto' is passed to the QEMU TCG to enable
> counting instructions the VM crashes with the following error report when
> Linux runs on it:
>
> qemu-system-ppc64: Bad icount read
>
> This happens because read/write access to the SPRs PURR, VTB, and TBU40
> is not integrated to the icount framework.
>
> This commit fixes that issue by making the read/write access of these
> SPRs aware of icount framework, adding the proper gen_io_start/end() calls
> before/after calling the helpers to load/store these SPRs in TCG.
>
> Signed-off-by: Gustavo Romero <gromero@linux.ibm.com>
> @@ -284,12 +284,26 @@ static void spr_write_atbu(DisasContext *ctx, int sprn, 
> int gprn)
>  ATTRIBUTE_UNUSED
>  static void spr_read_purr(DisasContext *ctx, int gprn, int sprn)
>  {
> +    if (tb_cflags(ctx->base.tb) & CF_USE_ICOUNT) {
> +        gen_io_start();
> +    }
>      gen_helper_load_purr(cpu_gpr[gprn], cpu_env);
> +    if (tb_cflags(ctx->base.tb) & CF_USE_ICOUNT) {
> +        gen_io_end();
> +        gen_stop_exception(ctx);
> +    }

You don't want to call gen_io_end; you just need to ensure that
you end the TB immediately after this insn. See
docs/devel/tcg-icount.rst.

thanks
-- PMM