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ARMv8-M FPCCR_S.TS from secure to secure

loquat3

I see ARMv8-M Arch.Ref.Manual.
One question.

Part. Exception entry, context stacking
From secure state to secure state,
If CONTROL.FPCA is 1 and FPCCR_S.TS is 1, additional FP context is stacked? (always?)

In case of additional state context, only secure to non-secure.
I seem difference.

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  • +1
    Hi,

    The additional FP state only needs to be stacked when going secure->non-secure to prevent non-secure SW seeing the secure values from registers S16-S31.

    "Regular" FP stacking only stacks the registers the procedure call standard classes as corruptible and trusts the handler to push/pop S16 upwards if it needs to use them.

    If Lazy FP state preservation is enabled then hardware might only reserve space in the stack from and stack the registers later.
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  • +1
    Hi,

    The additional FP state only needs to be stacked when going secure->non-secure to prevent non-secure SW seeing the secure values from registers S16-S31.

    "Regular" FP stacking only stacks the registers the procedure call standard classes as corruptible and trusts the handler to push/pop S16 upwards if it needs to use them.

    If Lazy FP state preservation is enabled then hardware might only reserve space in the stack from and stack the registers later.
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