Fix RV32 Zcherilevels ACPERM #440
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The modifications should have been for RV32 only, so this needs fixing |
src/insns/acperm_32bit.adoc
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| | 9 | <<sl_perm>> | <<c_perm>> | ||
| | 7 | <<el_perm>> | <<c_perm>> and <<r_perm>> and <<lm_perm>> | ||
| | 8 | <<lm_perm>> | <<c_perm>> and <<r_perm>> and (<<w_perm>> or <<el_perm>>) | ||
| | 9 | <<sl_perm>> | (<<c_perm>> and <<lm_perm>> and (<<x_perm>> or <<w_perm>>) |
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Do we really need to explicitly list LM here? I guess it's implied since SL depends on W, and W implies LM. Not opposed to keeping it since I imagine the checks will be optimized out but wondering if the text can be simplified.
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| | 9 | <<sl_perm>> | (<<c_perm>> and <<lm_perm>> and (<<x_perm>> or <<w_perm>>) | |
| | 9 (RV32 only) | <<sl_perm>> | (<<c_perm>> and <<lm_perm>> and (<<x_perm>> or <<w_perm>>) |
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yes - RV32 only was missing - will push a new commit soon
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this relates to rule 12 for the latest commit
if rule 12 is omitted then the following case fails:
Start: Perms(R=True, W=False, C=True, LM=True, EL=True, SL=True, X=False)
Final: Perms(R=True, W=False, C=True, LM=True, EL=True, SL=True, X=False)
(ASR has no bearing so is omitted - so in reality there are two failing cases)
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If you remove LM from the SL term in rule 9 there are 10 routes to get an invalid encoding, but they all end with the same permissions.
| R | W | C | LM | SL | X | Rule |
|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 0 | 1 | 1 | After & |
| 1 | 0 | 1 | 0 | 1 | 1 | Rule 5 - clear W |
| 1 | 0 | 1 | 0 | 1 | 1 | Rule 9 - but no LM inclusion (no change) |
| 1 | 0 | 1 | 0 | 1 | 0 | Rule 10 - clear X |
This leaves us with R, C, SL which doesn't map to any table entry. If you have LM as part of the rule, then you remove SL end at R, C.
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Rule 9 without LM does not clear SL because X is still HIGH, but SL needs to be aware of X because Quadrant 1, row 2/3 has W == 0 and C, LM, EL == 1 and SL == inf while Quadrant 3, row 3 has identical values for W, C, LM, EL however SL=0. So the only differentiator between these two cases is that in Quadrant 1 has X
This version has been verified by a python script which checks all possible combinations of removing permissions from maximum permissions
additional fix for #428