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da1c27df16
document `core::ffi::VaArgSafe` tracking issue: https://github.com/rust-lang/rust/issues/44930 A modification of https://github.com/rust-lang/rust/pull/146454, keeping just the documentation changes, but not unsealing the trait. Although conceptually we'd want to unseal the trait, there are many edge cases to supporting arbitrary types. We'd need to exhaustively test that all targets/calling conventions support all types that rust might generate (or generate proper error messages for unsupported cases). At present, many of the `va_arg` implementations assume that the argument is a scalar, and has an alignment of at most 8. That is totally sufficient for an MVP (accepting all of the "standard" C types), but clearly does not cover all rust types. This PR also adds some various other tests for edge cases of c-variadic: - the `#[inline]` attribute in its various forms. At present, LLVM is unable to inline c-variadic functions, but the attribute should still be accepted. `#[rustc_force_inline]` already rejects c-variadic functions. - naked functions should accept and work with a C variable argument list. In the future we'd like to allow more ABIs with naked functions (basically, any ABI for which we accept defining foreign c-variadic functions), but for now only `"C"` and `"C-unwind` are supported - guaranteed tail calls: c-variadic functions cannot be tail-called. That was already rejected, but there was not test for it. r? `@workingjubilee`
The files here use the LLVM FileCheck framework, documented at https://llvm.org/docs/CommandGuide/FileCheck.html.
One extension worth noting is the use of revisions as custom prefixes for FileCheck. If your codegen test has different behavior based on the chosen target or different compiler flags that you want to exercise, you can use a revisions annotation, like so:
// revisions: aaa bbb
// [bbb] compile-flags: --flags-for-bbb
After specifying those variations, you can write different expected, or
explicitly unexpected output by using <prefix>-SAME: and <prefix>-NOT:,
like so:
// CHECK: expected code
// aaa-SAME: emitted-only-for-aaa
// aaa-NOT: emitted-only-for-bbb
// bbb-NOT: emitted-only-for-aaa
// bbb-SAME: emitted-only-for-bbb