DNM/WIP: CHERI RISC-V f[su]{byte,...} fault lookaside table and As-user opcodes #1159
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This version has been corrected to not cause a return from the middle of an inlined function (d'oh!). Similar restructuring will be necessary for #1155, just haven't made time yet. |
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This defines the FSU_CHERI_AS_USER configuration knob and adjusts support.S to use it
This shows off the multiplicative impact of the two FSU optimisations: we don't need to call out to (and return from) an assember function and can instead inline a single instruction on the fast path. Right now this is just for fubyte, but in principle more of the fsu vocabulary is amenable to this treatment.
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A slightly different approach than #1155, but hopefully solving the same problem.
This adds two configuration knobs to let us explore faster
f[su]{byte,...}operations. Unlike #1155, this one avoids two pointer stores perf[su]*operation to store/remove the fault handler callback by, instead, adding a linker set "lookaside table" for fault handling behaviours. Presently, a closed taxonomy of such things, again. The fault handler has been enlightened to scan this lookaside table; it should support loadable modules but this has not been tested.As usual, commentary more than welcome.