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target/arm: default SVE length to 64 bytes for linux-user 

The Linux kernel chooses the default of 64 bytes for SVE registers on
the basis that it is the largest size on known hardware that won't
grow the signal frame. We still honour the sve-max-vq property and
userspace can expand the number of lanes by calling PR_SVE_SET_VL.

This should not make any difference to SVE enabled software as the SVE
is of course vector length agnostic.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

Message-Id: <20200316172155.971-18-alex.bennee@linaro.org>
This commit is contained in:
Alex Bennée 2020-03-16 17:21:44 +00:00
parent 32d6e32afa
commit 7b6a2198e7
1 changed files with 4 additions and 3 deletions
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7
target/arm/cpu.c
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@ -195,9 +195,10 @@ static void arm_cpu_reset(CPUState *s)
env->cp15.cpacr_el1 = deposit64(env->cp15.cpacr_el1, 20, 2, 3);
/* and to the SVE instructions */
env->cp15.cpacr_el1 = deposit64(env->cp15.cpacr_el1, 16, 2, 3);
/* with maximum vector length */
env->vfp.zcr_el[1] = cpu_isar_feature(aa64_sve, cpu) ?
cpu->sve_max_vq - 1 : 0;
/* with reasonable vector length */
if (cpu_isar_feature(aa64_sve, cpu)) {
env->vfp.zcr_el[1] = MIN(cpu->sve_max_vq - 1, 3);
}
/*
* Enable TBI0 and TBI1. While the real kernel only enables TBI0,
* turning on both here will produce smaller code and otherwise