On Thu, Sep 10, 2015 at 17:01:14 +0100, Alex Bennée wrote:
>
> Emilio G. Cota <c...@braap.org> writes:
>
> > Signed-off-by: Emilio G. Cota <c...@braap.org>
> > ---
> > tcg/tcg-op.h | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
> > diff --git a/tcg/tcg-op.h b/tcg/tcg-op.h
> > index 52482c0..3ec9f13 100644
> > --- a/tcg/tcg-op.h
> > +++ b/tcg/tcg-op.h
> > @@ -716,6 +716,16 @@ static inline void tcg_gen_fence_full(void)
> > tcg_gen_op0(&tcg_ctx, INDEX_op_fence_full);
> > }
> >
> > +#if defined(__i386__) || defined(__x86_64__) || defined(__s390x__)
> > +static inline void tcg_gen_smp_rmb(void)
> > +{ }
> > +#else
> > +static inline void tcg_gen_smp_rmb(void)
> > +{
> > + tcg_gen_fence_load();
> > +}
> > +#endif
>
> This seems a little pointless wrapping up tcg_gen_fence_load. Could the
> magic dealing with the backend not be done with something like
> TCG_TARGET_HAS_fence_load. On the x86/x86_64 backends this could then
> NOP away.
This patch made sense at the time as a companion to this other patch:
cpu: add barriers around cpu->tcg_exit_req
(snip)
+++ b/include/exec/gen-icount.h
@@ -16,6 +16,7 @@ static inline void gen_tb_start(TranslationBlock *tb)
exitreq_label = gen_new_label();
flag = tcg_temp_new_i32();
+ tcg_gen_smp_rmb();
tcg_gen_ld_i32(flag, cpu_env,
offsetof(CPUState, tcg_exit_req) - ENV_OFFSET);
tcg_gen_brcondi_i32(TCG_COND_NE, flag, 0, exitreq_label);
Paolo had the better idea of calling smp_rmb() once we've
exited TCG, which renders tcg_gen_smp_rmb() unnecessary.
Emilio
