Re: [Qemu-devel] [PATCH 02/15] target/arm: Don't trap WFI/WFE for M profile

[Edgar E. Iglesias]

On Wed, Aug 02, 2017 at 05:43:48PM +0100, Peter Maydell wrote:
> M profile cores can never trap on WFI or WFE instructions. Check for
> M profile in check_wfx_trap() to ensure this.
> 
> The existing code will do the right thing for v7M cores because
> the hcr_el2 and scr_el3 registers will be all-zeroes and so we
> won't attempt to trap, but when we start setting ARM_FEATURE_V8
> for v8M cores the v8A handling of SCTLR.nTWE and .nTWI will not
> give the right results.
> 
> Signed-off-by: Peter Maydell <address@hidden>

Reviewed-by: Edgar E. Iglesias <address@hidden>


> ---
>  target/arm/op_helper.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/target/arm/op_helper.c b/target/arm/op_helper.c
> index 2a85666..5a94a5f 100644
> --- a/target/arm/op_helper.c
> +++ b/target/arm/op_helper.c
> @@ -370,6 +370,11 @@ static inline int check_wfx_trap(CPUARMState *env, bool 
> is_wfe)
>      int cur_el = arm_current_el(env);
>      uint64_t mask;
>  
> +    if (arm_feature(env, ARM_FEATURE_M)) {
> +        /* M profile cores can never trap WFI/WFE. */
> +        return 0;
> +    }
> +
>      /* If we are currently in EL0 then we need to check if SCTLR is set up 
> for
>       * WFx instructions being trapped to EL1. These trap bits don't exist in 
> v7.
>       */
> -- 
> 2.7.4
> 
>