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Re: [PATCH v2 3/7] target/arm: Do not use aarch64_sve_zcr_get_valid_len
From: |
Peter Maydell |
Subject: |
Re: [PATCH v2 3/7] target/arm: Do not use aarch64_sve_zcr_get_valid_len in reset |
Date: |
Thu, 19 May 2022 11:40:07 +0100 |
On Tue, 17 May 2022 at 07:00, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> We don't need to constrain the value set in zcr_el[1],
> because it will be done by sve_zcr_len_for_el.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> target/arm/cpu.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index d2bd74c2ed..0621944167 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -208,8 +208,7 @@ static void arm_cpu_reset(DeviceState *dev)
> CPACR_EL1, ZEN, 3);
> /* with reasonable vector length */
> if (cpu_isar_feature(aa64_sve, cpu)) {
> - env->vfp.zcr_el[1] =
> - aarch64_sve_zcr_get_valid_len(cpu, cpu->sve_default_vq - 1);
> + env->vfp.zcr_el[1] = cpu->sve_default_vq - 1;
> }
Not all the code that looks at the sve vector length
goes through sve_zcr_len_for_el(), though. In particular,
this is setting up ZCR_EL1 for usermode, and all
the code under linux-user/ that wants to know the vector
length does it with "env->vfp.zcr_el[1] & 0xf".
More generally, it seems to me less confusing for debug
purposes if we set zcr_el[1] on reset to a valid value,
not to some invalid value that we're relying on being
coerced to something else at point of use.
Incidentally, do_prctl_set_vl() also sets zcr_el[1] and
it doesn't call aarch64_sve_zcr_get_valid_len(). Should it,
or is it doing an equivalent check anyway?
-- PMM
- [PATCH v2 0/7] target/arm: SME prep patches, Richard Henderson, 2022/05/17
- [PATCH v2 4/7] target/arm: Merge aarch64_sve_zcr_get_valid_len into caller, Richard Henderson, 2022/05/17
- [PATCH v2 6/7] target/arm: Remove fp checks from sve_exception_el, Richard Henderson, 2022/05/17
- [PATCH v2 1/7] target/arm: Enable FEAT_HCX for -cpu max, Richard Henderson, 2022/05/17
- [PATCH v2 2/7] target/arm: Use FIELD definitions for CPACR, CPTR_ELx, Richard Henderson, 2022/05/17
- [PATCH v2 3/7] target/arm: Do not use aarch64_sve_zcr_get_valid_len in reset, Richard Henderson, 2022/05/17
- Re: [PATCH v2 3/7] target/arm: Do not use aarch64_sve_zcr_get_valid_len in reset,
Peter Maydell <=
- [PATCH v2 5/7] target/arm: Use uint32_t instead of bitmap for sve vq's, Richard Henderson, 2022/05/17
- [PATCH v2 7/7] target/arm: Add el_is_in_host, Richard Henderson, 2022/05/17
- Re: [PATCH v2 0/7] target/arm: SME prep patches, Peter Maydell, 2022/05/19