target/arm: Clear AArch64 ID regs from ARMISARegisters if AArch64 disabled
If we create a normally-AArch64 CPU and configure it with
aarch64=off, this will by default leave all the AArch64 ID register
values in its ARMISARegisters struct untouched. That in turn means
that tests of cpu_isar_feature(aa64_something, cpu) will return true.
Until now we have had a design policy that you shouldn't check an
aa64_ feature unless you know that the CPU has AArch64; but this is
quite fragile as it's easy to forget and only causes a problem in the
corner case where AArch64 was turned off. In particular, when we
extend the ability to disable AArch64 from only KVM to also TCG there
are many more aa64 feature check points which we would otherwise have
to audit for whether they needed to be guarded with a check on
ARM_FEATURE_AARCH64.
Instead, make the CPU realize function zero out all the 64-bit ID
registers if the CPU doesn't have AArch64; this will make aa64_
feature tests generally return false.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
2 files changed