[CHERI] Fix Bounded Mem/Var Args layout on stack

[veselypeta]

Should fix #8 & #9 & #16

Includes change from #13

[dpgao]

This doesn't fix the first example in #8. The variadic argument of type Triple should begin at offset 16 of the memory argument buffer. But right now it begins at offset 8.

[dpgao]

And this doesn't fix the second example in #8. The call to f in g sets the memory argument buffer to NULL under -Xclang -target-feature -Xclang +cheri-bounded-vararg -Xclang -target-feature -Xclang +cheri-bounded-memarg-caller -Xclang -target-feature -Xclang +cheri-bounded-memarg-callee.

__uint128_t f(void* a, __uint128_t b, __uint128_t c, __uint128_t d, ...);

__uint128_t g() {
    return f((void*)0x1, 0, 0, 123, (__uint128_t)456, (__uint128_t)789);
}

[veselypeta]

Thanks @dpgao. It's proved quite tricky to get this right for RISCV. The issue I've come across is that Triple type is converted to [2 x i64] is llvm. In RISCV these are treated as separate arguments, but I need to align to up a slot boundary. I've made it work now, by picky backing on functionArgumentNeedsConsecutiveRegisters for purecap varargs. I think the layout is correct, now but I'm writing some tests for it now to make sure. Let me know if you still have any issues.
Thanks 🙏

[dpgao]

Thanks! I think once #14 is addressed, the compiler will be able to build CheriBSD with the memory argument ABI successfully.

[dpgao]

All LGTM now.

I've only been able to test this PR after rebasing it onto veselypeta/cherillvm@a7d84f5, so do you intend to merge this right now or wait until https://github.com/veselypeta/cherillvm/commits/codasip-rebased/ is first incorporated to the main branch here?

[veselypeta]

wait until https://github.com/veselypeta/cherillvm/commits/codasip-rebased/ is first incorporated to the main branch here?

Yes I'm working on integrating the last changes from both codasip and cambridge into this branch and make this the default branch for cheri alliance before merging this. Is this is a blocker for you, let me know, but it it seems that your rebase is working for your purpose. Hopefully, this will be the default branch by the end of the week. 🤞

[dpgao]

wait until https://github.com/veselypeta/cherillvm/commits/codasip-rebased/ is first incorporated to the main branch here?

Yes I'm working on integrating the last changes from both codasip and cambridge into this branch and make this the default branch for cheri alliance before merging this. Is this is a blocker for you, let me know, but it it seems that your rebase is working for your purpose. Hopefully, this will be the default branch by the end of the week. 🤞

Thank you! This is not a blocker for me at the moment but obviously it would be better if it gets merged.