Re: [Qemu-devel] [PATCH 4/4] target/arm: Implement tailchaining for M profile cores

[Richard Henderson]

On 07/20/2018 07:56 AM, Peter Maydell wrote:
> Tailchaining is an optimization in handling of exception return
> for M-profile cores: if we are about to pop the exception stack
> for an exception return, but there is a pending exception which
> is higher priority than the priority we are returning to, then
> instead of unstacking and then immediately taking the exception
> and stacking registers again, we can chain to the pending
> exception without unstacking and stacking.
> 
> For v6M and v7M it is IMPDEF whether tailchaining happens for pending
> exceptions; for v8M this is architecturally required.  Implement it
> in QEMU for all M-profile cores, since in practice v6M and v7M
> hardware implementations generally do have it.
> 
> (We were already doing tailchaining for derived exceptions which
> happened during exception return, like the validity checks and
> stack access failures; these have always been required to be
> tailchained for all versions of the architecture.)
> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  target/arm/helper.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)

Reviewed-by: Richard Henderson <address@hidden>


r~