custom VaList layout for Hexagon

[folkertdev]

I noticed while browsing LLVM source that we use an incorrect VaList definition for the musl hexagon target.

relevant links

• https://github.com/llvm/llvm-project/blob/0cdc1b6dd4a870fc41d4b15ad97e0001882aba58/clang/include/clang/Basic/TargetInfo.h#L333
• https://github.com/llvm/llvm-project/blob/0cdc1b6dd4a870fc41d4b15ad97e0001882aba58/clang/lib/CodeGen/Targets/Hexagon.cpp#L407-L417

cc target maintainer @androm3da can you confirm that this looks OK? In particular the #[rustc_pass_indirectly_in_non_rustic_abis] attribute is used to simulate pointer decay (like if the struct were wrapped in a 1-element array in C). The clang comment suggests that the Tag is wrapped in such a single-element array, but I haven't actually been able to confirm it.

For stabilizing c_variadic (on the hexagon targets) we will also need a custom va_arg implementation to mirror the one in clang in va_arg.rs. Would you be able to contribute one?

r? @workingjubilee

[rustbot]

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[androm3da]

can you confirm that this looks OK?

Thanks for the PR - I will give it a look!

[androm3da]

For stabilizing c_variadic (on the hexagon targets) we will also need a custom va_arg implementation to mirror the one in clang in va_arg.rs. Would you be able to contribute one?

Yeah - can do.

[folkertdev]

For stabilizing c_variadic (on the hexagon targets) we will also need a custom va_arg implementation to mirror the one in clang in va_arg.rs. Would you be able to contribute one?

Yeah - can do.

Nice, the relevant test here is ./x test tests/run-make/c-link-to-rust-va-list-fn --target hexagon-unknown-linux-musl.