On Tue, Jun 30, 2015 at 6:51 AM, Peter Maydell <peter.mayd...@linaro.org> wrote:
> Currently we use DISAS_WFE for both WFE and YIELD instructions.
> This is functionally correct because at the moment both of them
> are implemented as "yield this CPU back to the top level loop so
> another CPU has a chance to run". However it's rather confusing
> that YIELD ends up calling HELPER(wfe), and if we ever want to
> implement real behaviour for WFE and SEV it's likely to trip us up.
>
> Split out the yield codepath to use DISAS_YIELD and a new
> HELPER(yield) function, and have HELPER(wfe) call HELPER(yield).
>
> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwa...@xilinx.com>
> ---
> target-arm/helper.h | 1 +
> target-arm/op_helper.c | 18 +++++++++++++++---
> target-arm/translate-a64.c | 6 ++++++
> target-arm/translate.h | 1 +
> 4 files changed, 23 insertions(+), 3 deletions(-)
>
> diff --git a/target-arm/helper.h b/target-arm/helper.h
> index fc885de..827b33d 100644
> --- a/target-arm/helper.h
> +++ b/target-arm/helper.h
> @@ -50,6 +50,7 @@ DEF_HELPER_2(exception_internal, void, env, i32)
> DEF_HELPER_4(exception_with_syndrome, void, env, i32, i32, i32)
> DEF_HELPER_1(wfi, void, env)
> DEF_HELPER_1(wfe, void, env)
> +DEF_HELPER_1(yield, void, env)
> DEF_HELPER_1(pre_hvc, void, env)
> DEF_HELPER_2(pre_smc, void, env, i32)
>
> diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
> index 7fa32c4..663c05d 100644
> --- a/target-arm/op_helper.c
> +++ b/target-arm/op_helper.c
> @@ -323,13 +323,25 @@ void HELPER(wfi)(CPUARMState *env)
>
> void HELPER(wfe)(CPUARMState *env)
> {
> - CPUState *cs = CPU(arm_env_get_cpu(env));
> -
> - /* Don't actually halt the CPU, just yield back to top
> + /* This is a hint instruction that is semantically different
> + * from YIELD even though we currently implement it identically.
> + * Don't actually halt the CPU, just yield back to top
> * level loop. This is not going into a "low power state"
> * (ie halting until some event occurs), so we never take
> * a configurable trap to a different exception level.
> */
> + HELPER(yield)(env);
> +}
> +
> +void HELPER(yield)(CPUARMState *env)
> +{
> + ARMCPU *cpu = arm_env_get_cpu(env);
> + CPUState *cs = CPU(cpu);
> +
> + /* This is a non-trappable hint instruction that generally indicates
> + * that the guest is currently busy-looping. Yield control back to the
> + * top level loop so that a more deserving VCPU has a chance to run.
> + */
> cs->exception_index = EXCP_YIELD;
> cpu_loop_exit(cs);
> }
> diff --git a/target-arm/translate-a64.c b/target-arm/translate-a64.c
> index e077f2d..689f2be 100644
> --- a/target-arm/translate-a64.c
> +++ b/target-arm/translate-a64.c
> @@ -1199,6 +1199,8 @@ static void handle_hint(DisasContext *s, uint32_t insn,
> s->is_jmp = DISAS_WFI;
> return;
> case 1: /* YIELD */
> + s->is_jmp = DISAS_YIELD;
> + return;
> case 2: /* WFE */
> s->is_jmp = DISAS_WFE;
> return;
> @@ -11107,6 +11109,10 @@ void gen_intermediate_code_internal_a64(ARMCPU *cpu,
> gen_a64_set_pc_im(dc->pc);
> gen_helper_wfe(cpu_env);
> break;
> + case DISAS_YIELD:
> + gen_a64_set_pc_im(dc->pc);
> + gen_helper_yield(cpu_env);
> + break;
> case DISAS_WFI:
> /* This is a special case because we don't want to just halt the
> CPU
> * if trying to debug across a WFI.
> diff --git a/target-arm/translate.h b/target-arm/translate.h
> index bcdcf11..9ab978f 100644
> --- a/target-arm/translate.h
> +++ b/target-arm/translate.h
> @@ -103,6 +103,7 @@ static inline int default_exception_el(DisasContext *s)
> #define DISAS_WFE 7
> #define DISAS_HVC 8
> #define DISAS_SMC 9
> +#define DISAS_YIELD 10
>
> #ifdef TARGET_AARCH64
> void a64_translate_init(void);
> --
> 1.9.1
>
>
