On Tue, 11 Aug 2020 at 02:29, Gustavo Romero <grom...@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 <grom...@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
