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Re: [PATCH 08/10] target/arm: Fix has_vfp/has_neon ID reg squashing for

From: Richard Henderson
Subject: Re: [PATCH 08/10] target/arm: Fix has_vfp/has_neon ID reg squashing for M-profile
Date: Tue, 13 Oct 2020 12:07:44 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

On 10/12/20 8:37 AM, Peter Maydell wrote:
> In arm_cpu_realizefn(), if the CPU has VFP or Neon disabled then we
> squash the ID register fields so that we don't advertise it to the
> guest.  This code was written for A-profile and needs some tweaks to
> work correctly on M-profile:
>  * A-profile only fields should not be zeroed on M-profile:
>  * M-profile only fields should be zeroed on M-profile:
>    - MVFR1.FP16
> In particular, because MVFR1.SIMDHP on A-profile is the same field as
> MVFR1.FP16 on M-profile this code was incorrectly disabling FP16
> support on an M-profile CPU (where has_neon is always false).  This
> isn't a visible bug yet because we don't have any M-profile CPUs with
> FP16 support, but the change is necessary before we introduce any.
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  target/arm/cpu.c | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


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