bjoernager/rust
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implement unwinding abi's (RFC 2945)

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### Changes

    This commit implements unwind ABI's, specified in RFC 2945.

    We adjust the `rustc_middle::ty::layout::fn_can_unwind` function,
    used to compute whether or not a `FnAbi` object represents a
    function that should be able to unwind when `panic=unwind` is in
    use.

    Changes are also made to
    `rustc_mir_build::build::should_abort_on_panic` so that the
    function ABI is used to determind whether it should abort, assuming
    that the `panic=unwind` strategy is being used, and no explicit
    unwind attribute was provided.

 ### Tests

    Unit tests, checking that the behavior is correct for `C-unwind`,
    `stdcall-unwind`, `system-unwind`, and `thiscall-unwind`, are
    included. These alternative `unwind` ABI strings are specified in
    RFC 2945, in the "_Other `unwind` ABI strings_" section.

    Additionally, a test case is included to assert that the LLVM IR
    generated for an external function defined with the `C-unwind` ABI
    will be appropriately labeled with the `nounwind` LLVM attribute
    when the `panic=abort` compilation flag is used.

 ### Ignore Directives

    This commit uses `ignore-*` directives 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 commit is contained in:
katelyn a. martin 2020-09-10 13:38:39 -04:00
parent df45c579de
commit 0f33e9f281
7 changed files with 176 additions and 16 deletions
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22
compiler/rustc_mir_build/src/build/mod.rs
View file

@ -548,7 +548,7 @@ macro_rules! unpack {
}};
}
fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, _abi: Abi) -> bool {
fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, abi: Abi) -> bool {
// Validate `#[unwind]` syntax regardless of platform-specific panic strategy.
let attrs = &tcx.get_attrs(fn_def_id.to_def_id());
let unwind_attr = attr::find_unwind_attr(&tcx.sess, attrs);
@ -558,12 +558,26 @@ fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, _abi: Abi) -> b
return false;
}
// This is a special case: some functions have a C abi but are meant to
// unwind anyway. Don't stop them.
match unwind_attr {
None => false, // FIXME(#58794); should be `!(abi == Abi::Rust || abi == Abi::RustCall)`
// If an `#[unwind]` attribute was found, we should adhere to it.
Some(UnwindAttr::Allowed) => false,
Some(UnwindAttr::Aborts) => true,
// If no attribute was found and the panic strategy is `unwind`, then we should examine
// the function's ABI string to determine whether it should abort upon panic.
None => {
use Abi::*;
match abi {
// In the case of ABI's that have an `-unwind` equivalent, check whether the ABI
// permits unwinding. If so, we should not abort. Otherwise, we should.
C { unwind } | Stdcall { unwind } | System { unwind } | Thiscall { unwind } => {
!unwind
}
// Rust and `rust-call` functions are allowed to unwind, and should not abort.
Rust | RustCall => false,
// Other ABI's should abort.
_ => true,
}
}
}
}