[CHERI-RISC-V] Restrict CToPtr and CFromPtr usage to ISAv8 compatibility #711
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CToPtr will be removed from the CHERI-RISC-V ISA in the future and will not be part of a standardized version. We emit a branch-less form of `x.tag ? x.addr - auth.base : 0` when we see the intrinsic in non-ISAv8 compilation mode instead. When expanding `ptrtoint` in hybrid mode we also no longer subtract the base of DDC as part of the expansion, since DDC relocation is no longer part of xcherimin, and subtracting the base would result in an integer that points to a different address when dereferenced.
We emit `x == 0 ? null : CSetOffset(auth, x)` when we see the intrinsic in non-ISAv8 compilation mode instead. When expanding `inttoptr` in hybrid mode, we do not include the base of DDC as part of the expansion (since DDC relocation is no longer part of ISAv9). Adding the base would result in a capability that points to a different address when dereferenced. Therefore, inttoptr is expanded to `x == 0 ? null : CSetAddr(DDC, x)`. It would be nice if we could just use `CSetAddr(DDC, x)` unconditionally for non-constant arguments, but that could result in semantic differences (tagged vs untagged) for integers that happen to be zero at run time.
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Do we want to add a deprecation warning to the intrinsics perhaps so that we can eventually drop them (or have them only be valid when you have the underlying instructions)? |
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Closing this in favour of #708 |
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