The M-profile architecture requires that accesses to FPCXT_NS when
there is no active FP state must not take a NOCP fault even if the
FPU is disabled. We were not implementing this correctly, because
in our decode we catch the NOCP faults early in m-nocp.decode.
Fix this bug by moving all the handling of M-profile FP system
register accesses from vfp.decode into m-nocp.decode and putting
it above the NOCP blocks. This provides the correct behaviour:
* for accesses other than FPCXT_NS the trans functions call
vfp_access_check(), which will check for FPU disabled and
raise a NOCP exception if necessary
* for FPCXT_NS we have the special case code that doesn't
call vfp_access_check()
* when these trans functions want to raise an UNDEF they return
false, so the decoder will fall through into the NOCP blocks.
This means that NOCP correctly takes precedence over UNDEF
for these insns. (This is a difference from the other insns
handled by m-nocp.decode, where UNDEF takes precedence and
which we implement by having those trans functions call
unallocated_encoding() in the appropriate places.)
[Note for backport to stable: this commit has a semantic dependency
on commit 9a486856e9, which was not marked as cc-stable because
we didn't know we'd need it for a for-stable bugfix.]
Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210618141019.10671-4-peter.maydell@linaro.org
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