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target/arm: Make sure M-profile FPSCR RES0 bits are not settable 

Enforce that for M-profile various FPSCR bits which are RES0 there
but have defined meanings on A-profile are never settable. This
ensures that M-profile code can't enable the A-profile behaviour
(notably vector length/stride handling) by accident.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190416125744.27770-2-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2019-04-29 17:35:58 +01:00
parent 79d77bcd36
commit 5bcf8ed940
1 changed files with 8 additions and 0 deletions
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8
target/arm/vfp_helper.c
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@ -105,6 +105,14 @@ void HELPER(vfp_set_fpscr)(CPUARMState *env, uint32_t val)
val &= ~FPCR_FZ16;
}
if (arm_feature(env, ARM_FEATURE_M)) {
/*
* M profile FPSCR is RES0 for the QC, STRIDE, FZ16, LEN bits
* and also for the trapped-exception-handling bits IxE.
*/
val &= 0xf7c0009f;
}
/*
* We don't implement trapped exception handling, so the
* trap enable bits, IDE|IXE|UFE|OFE|DZE|IOE are all RAZ/WI (not RES0!)