bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

rustc_target: add "unwind" payloads to Abi

Browse source 
### Overview

    This commit begins the implementation work for RFC 2945. For more
    information, see the rendered RFC [1] and tracking issue [2].

    A boolean `unwind` payload is added to the `C`, `System`, `Stdcall`,
    and `Thiscall` variants, marking whether unwinding across FFI
    boundaries is acceptable. The cases where each of these variants'
    `unwind` member is true correspond with the `C-unwind`,
    `system-unwind`, `stdcall-unwind`, and `thiscall-unwind` ABI strings
    introduced in RFC 2945 [3].

 ### Feature Gate and Unstable Book

    This commit adds a `c_unwind` feature gate for the new ABI strings.
    Tests for this feature gate are included in `src/test/ui/c-unwind/`,
    which ensure that this feature gate works correctly for each of the
    new ABIs.

    A new language features entry in the unstable book is added as well.

 ### Further Work To Be Done

    This commit does not proceed to implement the new unwinding ABIs,
    and is intentionally scoped specifically to *defining* the ABIs and
    their feature flag.

 ### One Note on Test Churn

    This will lead to some test churn, in re-blessing hash tests, as the
    deleted comment in `src/librustc_target/spec/abi.rs` mentioned,
    because we can no longer guarantee the ordering of the `Abi`
    variants.

    While this is a downside, this decision was made bearing in mind
    that RFC 2945 states the following, in the "Other `unwind` Strings"
    section [3]:

    >  More unwind variants of existing ABI strings may be introduced,
    >  with the same semantics, without an additional RFC.

    Adding a new variant for each of these cases, rather than specifying
    a payload for a given ABI, would quickly become untenable, and make
    working with the `Abi` enum prone to mistakes.

    This approach encodes the unwinding information *into* a given ABI,
    to account for the future possibility of other `-unwind` ABI
    strings.

 ### Ignore Directives

    `ignore-*` directives are used in two of our `*-unwind` ABI test
    cases.

    Specifically, the `stdcall-unwind` and `thiscall-unwind` test cases
    ignore architectures that do not support `stdcall` and
    `thiscall`, respectively.

    These directives are cribbed from
    `src/test/ui/c-variadic/variadic-ffi-1.rs` for `stdcall`, and
    `src/test/ui/extern/extern-thiscall.rs` for `thiscall`.

    This would otherwise fail on some targets, see:
    fcf697f902

 ### Footnotes

[1]: https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md
[2]: https://github.com/rust-lang/rust/issues/74990
[3]: https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md#other-unwind-abi-strings
This commit is contained in:
katelyn a. martin 2020-08-27 11:49:18 -04:00
parent 3a5d45f68c
commit df45c579de
29 changed files with 277 additions and 52 deletions
Download patch file Download diff file Expand all files Collapse all files

2
compiler/rustc_typeck/src/collect.rs
View file

@ -2666,7 +2666,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
} else if tcx.sess.check_name(attr, sym::used) {
codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
} else if tcx.sess.check_name(attr, sym::cmse_nonsecure_entry) {
if tcx.fn_sig(id).abi() != abi::Abi::C {
if !matches!(tcx.fn_sig(id).abi(), abi::Abi::C { .. }) {
struct_span_err!(
tcx.sess,
attr.span,

21
compiler/rustc_typeck/src/lib.rs
View file

@ -118,14 +118,19 @@ use astconv::AstConv;
use bounds::Bounds;
fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
let mut err = struct_span_err!(
tcx.sess,
span,
E0045,
"C-variadic function must have C or cdecl calling convention"
);
err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
match (decl.c_variadic, abi) {
// The function has the correct calling convention, or isn't a "C-variadic" function.
(false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl) => {}
// The function is a "C-variadic" function with an incorrect calling convention.
(true, _) => {
let mut err = struct_span_err!(
tcx.sess,
span,
E0045,
"C-variadic function must have C or cdecl calling convention"
);
err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
}
}
}