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target/arm: Handle SVE vector length changes in system mode

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SVE vector length can change when changing EL, or when writing
to one of the ZCR_ELn registers.

For correctness, our implementation requires that predicate bits
that are inaccessible are never set.  Which means noticing length
changes and zeroing the appropriate register bits.

Tested-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20181005175350.30752-5-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Richard Henderson 2018-10-08 14:55:02 +01:00 • committed by Peter Maydell
parent 2de7ace292
commit 0ab5953b00
4 changed files with 125 additions and 55 deletions
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42
target/arm/cpu64.c
View file

@ -410,45 +410,3 @@ static void aarch64_cpu_register_types(void)
}
type_init(aarch64_cpu_register_types)
/* The manual says that when SVE is enabled and VQ is widened the
* implementation is allowed to zero the previously inaccessible
* portion of the registers. The corollary to that is that when
* SVE is enabled and VQ is narrowed we are also allowed to zero
* the now inaccessible portion of the registers.
*
* The intent of this is that no predicate bit beyond VQ is ever set.
* Which means that some operations on predicate registers themselves
* may operate on full uint64_t or even unrolled across the maximum
* uint64_t[4]. Performing 4 bits of host arithmetic unconditionally
* may well be cheaper than conditionals to restrict the operation
* to the relevant portion of a uint16_t[16].
*
* TODO: Need to call this for changes to the real system registers
* and EL state changes.
*/
void aarch64_sve_narrow_vq(CPUARMState *env, unsigned vq)
{
int i, j;
uint64_t pmask;
assert(vq >= 1 && vq <= ARM_MAX_VQ);
assert(vq <= arm_env_get_cpu(env)->sve_max_vq);
/* Zap the high bits of the zregs. */
for (i = 0; i < 32; i++) {
memset(&env->vfp.zregs[i].d[2 * vq], 0, 16 * (ARM_MAX_VQ - vq));
}
/* Zap the high bits of the pregs and ffr. */
pmask = 0;
if (vq & 3) {
pmask = ~(-1ULL << (16 * (vq & 3)));
}
for (j = vq / 4; j < ARM_MAX_VQ / 4; j++) {
for (i = 0; i < 17; ++i) {
env->vfp.pregs[i].p[j] &= pmask;
}
pmask = 0;
}
}