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Re: [PATCH 5/7] target/arm: Do M-profile NOCP checks early and via decod

From: Richard Henderson
Subject: Re: [PATCH 5/7] target/arm: Do M-profile NOCP checks early and via decodetree
Date: Tue, 4 Aug 2020 20:04:24 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

On 8/3/20 4:18 AM, Peter Maydell wrote:
> For M-profile CPUs, the architecture specifies that the NOCP
> exception when a coprocessor is not present or disabled should cover
> the entire wide range of coprocessor-space encodings, and should take
> precedence over UNDEF exceptions.  (This is the opposite of
> A-profile, where checking for a disabled FPU has to happen last.)
> Implement this with decodetree patterns that cover the specified
> ranges of the encoding space.  There are a few instructions (VLLDM,
> VLSTM, and in v8.1 also VSCCLRM) which are in copro-space but must
> not be NOCP'd: these must be handled also in the new m-nocp.decode so
> they take precedence.
> This is a minor behaviour change: for unallocated insn patterns in
> the VFP area (cp=10,11) we will now NOCP rather than UNDEF when the
> FPU is disabled.
> As well as giving us the correct architectural behaviour for v8.1M
> and the recommended behaviour for v8.0M, this refactoring also
> removes the old NOCP handling from the remains of the 'legacy
> decoder' in disas_thumb2_insn(), paving the way for cleaning that up.
> Since we don't currently have a v8.1M feature bit or any v8.1M CPUs,
> the minor changes to this logic that we'll need for v8.1M are marked
> up with TODO comments.
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

> +        /* M-profile handled this earlier, in disas_m_profile_nocp() */

That's not the function name you settled upon.


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