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katelyn a. martin df45c579de rustc_target: add "unwind" payloads to `Abi` ### 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	2021-03-09 14:38:29 -05:00
..
src	rustc_target: add "unwind" payloads to `Abi`	2021-03-09 14:38:29 -05:00
Cargo.toml	Update to rustc-demangle 0.1.18	2020-10-21 21:11:11 +01:00

katelyn a. martin df45c579de rustc_target: add "unwind" payloads to Abi

### 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

2021-03-09 14:38:29 -05:00

src rustc_target: add "unwind" payloads to Abi 2021-03-09 14:38:29 -05:00

Cargo.toml Update to rustc-demangle 0.1.18 2020-10-21 21:11:11 +01:00