Enable the Arm Cortex-A53 errata mitigation on aarch64-unknown-none
Arm Cortex-A53 CPUs have an errata related to a specific sequence of instructions - errata number 843419 (https://documentation-service.arm.com/static/5fa29fddb209f547eebd361d). There is a mitigation that can be applied at link-time which detects the when sequence of instructions exists at a specific alignment. When detected, the linker re-writes those instructions and either changes an ADRP to an ADR, or bounces to a veneer to break the sequence.
The linker argument to enable the mitigation is "--fix-cortex-a53-843419", and this is supported by GNU ld and LLVM lld. The gcc argument to enable the flag is "-mfix-cortex-a53-843419".
Because the aarch64-unknown-none target uses rust-lld directly, this patch causes rustc to emit the "--fix-cortex-a53-843419" argument when calling the linker, just like aarch64-linux-gnu-gcc on Ubuntu 22.04 does.
Failure to enable this mitigation in the linker can cause the production of instruction sequences that do not execute correctly on Arm Cortex-A53.
By default, `newtype_index!` types get a default `Encodable`/`Decodable`
impl. You can opt out of this with `custom_encodable`. Opting out is the
opposite to how Rust normally works with autogenerated (derived) impls.
This commit inverts the behaviour, replacing `custom_encodable` with
`encodable` which opts into the default `Encodable`/`Decodable` impl.
Only 23 of the 59 `newtype_index!` occurrences need `encodable`.
Even better, there were eight crates with a dependency on
`rustc_serialize` just from unused default `Encodable`/`Decodable`
impls. This commit removes that dependency from those eight crates.
Arm Cortex-A53 CPUs have an errata related to a specific sequence of instructions - errata number 843419 (https://documentation-service.arm.com/static/5fa29fddb209f547eebd361d). There is a mitigation that can be applied at link-time which detects the when sequence of instructions exists at a specific alignment. When detected, the linker re-writes those instructions and either changes an ADRP to an ADR, or bounces to a veneer to break the sequence.
The linker argument to enable the mitigation is "--fix-cortex-a53-843419", and this is supported by GNU ld and LLVM lld. The gcc argument to enable the flag is "-mfix-cortex-a53-843419".
Because the aarch64-unknown-none target uses rust-lld directly, this patch causes rustc to emit the "--fix-cortex-a53-843419" argument when calling the linker, just like aarch64-linux-gnu-gcc on Ubuntu 22.04 does.
Failure to enable this mitigation in the linker can cause the production of instruction sequences that do not execute correctly on Arm Cortex-A53.
Add arm64e-apple-ios & arm64e-apple-darwin targets
This introduces
* `arm64e-apple-ios`
* `arm64e-apple-darwin`
Rust targets for support `arm64e` architecture on `iOS` and `Darwin`.
So, this is a first approach for integrating to the Rust compiler.
## Tier 3 Target Policy
> * A tier 3 target must have a designated developer or developers (the "target
maintainers") on record to be CCed when issues arise regarding the target.
(The mechanism to track and CC such developers may evolve over time.)
I will be the target maintainer.
> * Targets must use naming consistent with any existing targets; for instance, a
target for the same CPU or OS as an existing Rust target should use the same
name for that CPU or OS. Targets should normally use the same names and
naming conventions as used elsewhere in the broader ecosystem beyond Rust
(such as in other toolchains), unless they have a very good reason to
diverge. Changing the name of a target can be highly disruptive, especially
once the target reaches a higher tier, so getting the name right is important
even for a tier 3 target.
Target names should not introduce undue confusion or ambiguity unless
absolutely necessary to maintain ecosystem compatibility. For example, if
the name of the target makes people extremely likely to form incorrect
beliefs about what it targets, the name should be changed or augmented to
disambiguate it.
If possible, use only letters, numbers, dashes and underscores for the name.
Periods (.) are known to cause issues in Cargo.
The target names `arm64e-apple-ios`, `arm64e-apple-darwin` were derived from `aarch64-apple-ios`, `aarch64-apple-darwin`.
In this [ticket,](#73628) people discussed the best suitable names for these targets.
> In some cases, the arm64e arch might be "different". For example:
> * `thread_set_state` might fail with (os/kern) protection failure if we try to call it from arm64 process to arm64e process.
> * The returning value of dlsym is PAC signed on arm64e, while left untouched on arm64
> * Some function like pthread_create_from_mach_thread requires a PAC signed function pointer on arm64e, which is not required on arm64.
So, I have chosen them because there are similar triplets in LLVM. I think there are no more suitable names for these targets.
> * Tier 3 targets may have unusual requirements to build or use, but must not
create legal issues or impose onerous legal terms for the Rust project or for
Rust developers or users.
The target must not introduce license incompatibilities.
Anything added to the Rust repository must be under the standard Rust
license (MIT OR Apache-2.0).
The target must not cause the Rust tools or libraries built for any other
host (even when supporting cross-compilation to the target) to depend
on any new dependency less permissive than the Rust licensing policy. This
applies whether the dependency is a Rust crate that would require adding
new license exceptions (as specified by the tidy tool in the
rust-lang/rust repository), or whether the dependency is a native library
or binary. In other words, the introduction of the target must not cause a
user installing or running a version of Rust or the Rust tools to be
subject to any new license requirements.
Compiling, linking, and emitting functional binaries, libraries, or other
code for the target (whether hosted on the target itself or cross-compiling
from another target) must not depend on proprietary (non-FOSS) libraries.
Host tools built for the target itself may depend on the ordinary runtime
libraries supplied by the platform and commonly used by other applications
built for the target, but those libraries must not be required for code
generation for the target; cross-compilation to the target must not require
such libraries at all. For instance, rustc built for the target may
depend on a common proprietary C runtime library or console output library,
but must not depend on a proprietary code generation library or code
optimization library. Rust's license permits such combinations, but the
Rust project has no interest in maintaining such combinations within the
scope of Rust itself, even at tier 3.
"onerous" here is an intentionally subjective term. At a minimum, "onerous"
legal/licensing terms include but are not limited to: non-disclosure
requirements, non-compete requirements, contributor license agreements
(CLAs) or equivalent, "non-commercial"/"research-only"/etc terms,
requirements conditional on the employer or employment of any particular
Rust developers, revocable terms, any requirements that create liability
for the Rust project or its developers or users, or any requirements that
adversely affect the livelihood or prospects of the Rust project or its
developers or users.
No dependencies were added to Rust.
> * Neither this policy nor any decisions made regarding targets shall create any
binding agreement or estoppel by any party. If any member of an approving
Rust team serves as one of the maintainers of a target, or has any legal or
employment requirement (explicit or implicit) that might affect their
decisions regarding a target, they must recuse themselves from any approval
decisions regarding the target's tier status, though they may otherwise
participate in discussions.
> * This requirement does not prevent part or all of this policy from being
cited in an explicit contract or work agreement (e.g. to implement or
maintain support for a target). This requirement exists to ensure that a
developer or team responsible for reviewing and approving a target does not
face any legal threats or obligations that would prevent them from freely
exercising their judgment in such approval, even if such judgment involves
subjective matters or goes beyond the letter of these requirements.
Understood.
I am not a member of a Rust team.
> * Tier 3 targets should attempt to implement as much of the standard libraries
as possible and appropriate (core for most targets, alloc for targets
that can support dynamic memory allocation, std for targets with an
operating system or equivalent layer of system-provided functionality), but
may leave some code unimplemented (either unavailable or stubbed out as
appropriate), whether because the target makes it impossible to implement or
challenging to implement. The authors of pull requests are not obligated to
avoid calling any portions of the standard library on the basis of a tier 3
target not implementing those portions.
Understood.
`std` is supported.
> * The target must provide documentation for the Rust community explaining how
to build for the target, using cross-compilation if possible. If the target
supports running binaries, or running tests (even if they do not pass), the
documentation must explain how to run such binaries or tests for the target,
using emulation if possible or dedicated hardware if necessary.
Building is described in the derived target doc.
> * Tier 3 targets must not impose burden on the authors of pull requests, or
other developers in the community, to maintain the target. In particular,
do not post comments (automated or manual) on a PR that derail or suggest a
block on the PR based on a tier 3 target. Do not send automated messages or
notifications (via any medium, including via `@)` to a PR author or others
involved with a PR regarding a tier 3 target, unless they have opted into
such messages.
> * Backlinks such as those generated by the issue/PR tracker when linking to
an issue or PR are not considered a violation of this policy, within
reason. However, such messages (even on a separate repository) must not
generate notifications to anyone involved with a PR who has not requested
such notifications.
Understood.
> * Patches adding or updating tier 3 targets must not break any existing tier 2
or tier 1 target, and must not knowingly break another tier 3 target without
approval of either the compiler team or the maintainers of the other tier 3
target.
> * In particular, this may come up when working on closely related targets,
such as variations of the same architecture with different features. Avoid
introducing unconditional uses of features that another variation of the
target may not have; use conditional compilation or runtime detection, as
appropriate, to let each target run code supported by that target.
These targets are not fully ABI compatible with arm64e code.
#73628
Ensure sanity of all computed ABIs
This moves the ABI sanity assertions from the codegen backend to the ABI computation logic. Sadly, due to past mistakes, we [have to](https://github.com/rust-lang/rust/pull/117351#issuecomment-1788495503) be able to compute a sane ABI for nonsensical function types like `extern "C" fn(str) -> str`. So to make the sanity check pass we first need to make all ABI adjustment deal with unsized types... and we have no shared infrastructure for those adjustments, so that's a bunch of copy-paste. At least we have assertions failing loudly when one accidentally sets a different mode for an unsized argument.
To achieve this, this re-lands the parts of https://github.com/rust-lang/rust/pull/80594 that got reverted in https://github.com/rust-lang/rust/pull/81388. To avoid breaking wasm ABI again, that ABI now explicitly opts-in to the (wrong, broken) ABI that we currently keep for backwards compatibility. That's still better than having *every* ABI use the wrong broken default!
Cc `@bjorn3`
Fixes https://github.com/rust-lang/rust/issues/115845
Remove asmjs
Fulfills [MCP 668](https://github.com/rust-lang/compiler-team/issues/668).
`asmjs-unknown-emscripten` does not work as-specified, and lacks essential upstream support for generating asm.js, so it should not exist at all.
Add `std:#️⃣:{DefaultHasher, RandomState}` exports (needs FCP)
This implements rust-lang/libs-team#267 to move the libstd hasher types to `std::hash` where they belong, instead of `std::collections::hash_map`.
<details><summary>The below no longer applies, but is kept for clarity.</summary>
This is a small refactor for #27242, which moves the definitions of `RandomState` and `DefaultHasher` into `std::hash`, but in a way that won't be noticed in the public API.
I've opened rust-lang/libs-team#267 as a formal ACP to move these directly into the root of `std::hash`, but for now, they're at least separated out from the collections code in a way that will make moving that around easier.
I decided to simply copy the rustdoc for `std::hash` from `core::hash` since I think it would be ideal for the two to diverge longer-term, especially if the ACP is accepted. However, I would be willing to factor them out into a common markdown document if that's preferred.
</details>
Set max_atomic_width for riscv32*-esp-espidf to 32
Fixes#117305
> Since riscv32 does not have 64-bit atomic instructions, I do not believe there is any way to fix this problem other than setting max_atomic_width of these targets to 32.
This is a breaking change because Atomic\*64 will become unavailable, but all affected targets are tier 3, and the current Atomic*64 violates the standard library's API contract and can cause problems with code that rely on the standard library's atomic types being lock-free.
r? `@Amanieu`
cc `@ivmarkov` `@MabezDev`
- Sort dependencies and features sections.
- Add `tidy` markers to the sorted sections so they stay sorted.
- Remove empty `[lib`] sections.
- Remove "See more keys..." comments.
Excluded files:
- rustc_codegen_{cranelift,gcc}, because they're external.
- rustc_lexer, because it has external use.
- stable_mir, because it has external use.
Declare rustc_target's dependency on object/macho
Without this, `cargo check` fails in crates that depend on rustc_target.
<details>
<summary>`cargo check` diagnostics</summary>
```console
Checking rustc_target v0.0.0
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:176:17
|
176 | object::macho::PLATFORM_MACOS => Some((13, 1)),
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:177:17
|
177 | object::macho::PLATFORM_IOS
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:178:19
|
178 | | object::macho::PLATFORM_IOSSIMULATOR
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:179:19
|
179 | | object::macho::PLATFORM_TVOS
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:180:19
|
180 | | object::macho::PLATFORM_TVOSSIMULATOR
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:181:19
|
181 | | object::macho::PLATFORM_MACCATALYST => Some((16, 2)),
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:182:17
|
182 | object::macho::PLATFORM_WATCHOS | object::macho::PLATFORM_WATCHOSSIMULATOR => Some((9, 1)),
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:182:51
|
182 | object::macho::PLATFORM_WATCHOS | object::macho::PLATFORM_WATCHOSSIMULATOR => Some((9, 1)),
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:189:33
|
189 | ("macos", _) => object::macho::PLATFORM_MACOS,
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:190:38
|
190 | ("ios", "macabi") => object::macho::PLATFORM_MACCATALYST,
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:191:35
|
191 | ("ios", "sim") => object::macho::PLATFORM_IOSSIMULATOR,
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:192:31
|
192 | ("ios", _) => object::macho::PLATFORM_IOS,
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:193:39
|
193 | ("watchos", "sim") => object::macho::PLATFORM_WATCHOSSIMULATOR,
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:194:35
|
194 | ("watchos", _) => object::macho::PLATFORM_WATCHOS,
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:195:36
|
195 | ("tvos", "sim") => object::macho::PLATFORM_TVOSSIMULATOR,
| ^^^^^ could not find `macho` in `object`
error[E0433]: failed to resolve: could not find `macho` in `object`
--> compiler/rustc_target/src/spec/apple_base.rs:196:32
|
196 | ("tvos", _) => object::macho::PLATFORM_TVOS,
| ^^^^^ could not find `macho` in `object`
```
</details>
`rustc_target` unconditionally contains its `spec` module (i.e. there is no `#[cfg]` on the `mod spec;`). The `spec/mod.rs` also does not start with `#![cfg]`.
aa91057796/compiler/rustc_target/src/lib.rs (L37)
Similarly, the `spec` module unconditionally contains `apple_base`.
aa91057796/compiler/rustc_target/src/spec/mod.rs (L62)
And, `apple_base` unconditionally refers to `object::macho`.
aa91057796/compiler/rustc_target/src/spec/apple_base.rs (L176)
So I figure there is no way `object::macho` isn't needed by rustc.
`object::macho` only exists if the `object` crate's "macho" feature is enabled. https://github.com/gimli-rs/object/blob/0.32.0/src/lib.rs#L111-L112
Add support for i586-unknown-netbsd as target.
This restricts instructions to those offered by Pentium, to support e.g. AMD Geode.
There is already an entry for this target in the NetBSD platform support page at
src/doc/rustc/src/platform-support/netbsd.md
...so this should forestall its removal.
Additional fixes are needed for some vendored modules, this is the changes in the rust compiler core itself.
tvOS simulator support on Apple Silicon for rustc
Closes or is a subtask of #115692.
# Tier 3 Target Policy
At this tier, the Rust project provides no official support for a target, so we place minimal requirements on the introduction of targets.
> * A tier 3 target must have a designated developer or developers (the "target maintainers") on record to be CCed when issues arise regarding the target. (The mechanism to track and CC such developers may evolve over time.)
See [`src/doc/rustc/src/platform-support/apple-tvos.md`](4ab4d48ee5/src/doc/rustc/src/platform-support/apple-tvos.md)
> * Targets must use naming consistent with any existing targets; for instance, a target for the same CPU or OS as an existing Rust target should use the same name for that CPU or OS. Targets should normally use the same names and naming conventions as used elsewhere in the broader ecosystem beyond Rust (such as in other toolchains), unless they have a very good reason to diverge. Changing the name of a target can be highly disruptive, especially once the target reaches a higher tier, so getting the name right is important even for a tier 3 target.
> * Target names should not introduce undue confusion or ambiguity unless absolutely necessary to maintain ecosystem compatibility. For example, if the name of the target makes people extremely likely to form incorrect beliefs about what it targets, the name should be changed or augmented to disambiguate it.
> * If possible, use only letters, numbers, dashes and underscores for the name. Periods (.) are known to cause issues in Cargo.
This naming scheme matches `$ARCH-$VENDOR-$OS-$ABI` (I think `sim` is the ABI here) which is matches the iOS apple silicon simulator (`aarch64-apple-ios-sim`). [There is some discussion about renaming some apple simulator targets](https://github.com/rust-lang/rust/issues/115692#issuecomment-1712931910) to match the `-sim` suffix but that is outside the scope of this PR.
> * Tier 3 targets may have unusual requirements to build or use, but must not create legal issues or impose onerous legal terms for the Rust project or for Rust developers or users.
>
> * The target must not introduce license incompatibilities.
> * Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).
> * The target must not cause the Rust tools or libraries built for any other host (even when supporting cross-compilation to the target) to depend on any new dependency less permissive than the Rust licensing policy. This applies whether the dependency is a Rust crate that would require adding new license exceptions (as specified by the tidy tool in the rust-lang/rust repository), or whether the dependency is a native library or binary. In other words, the introduction of the target must not cause a user installing or running a version of Rust or the Rust tools to be subject to any new license requirements.
> * Compiling, linking, and emitting functional binaries, libraries, or other code for the target (whether hosted on the target itself or cross-compiling from another target) must not depend on proprietary (non-FOSS) libraries. Host tools built for the target itself may depend on the ordinary runtime libraries supplied by the platform and commonly used by other applications built for the target, but those libraries must not be required for code generation for the target; cross-compilation to the target must not require such libraries at all. For instance, rustc built for the target may depend on a common proprietary C runtime library or console output library, but must not depend on a proprietary code generation library or code optimization library. Rust's license permits such combinations, but the Rust project has no interest in maintaining such combinations within the scope of Rust itself, even at tier 3.
> * "onerous" here is an intentionally subjective term. At a minimum, "onerous" legal/licensing terms include but are not limited to: non-disclosure requirements, non-compete requirements, contributor license agreements (CLAs) or equivalent, "non-commercial"/"research-only"/etc terms, requirements conditional on the employer or employment of any particular Rust developers, revocable terms, any requirements that create liability for the Rust project or its developers or users, or any requirements that adversely affect the livelihood or prospects of the Rust project or its developers or users.
This contribution is fully available under the standard Rust license with no additional legal restrictions whatsoever. This PR does not introduce any new dependency less permissive than the Rust license policy.
The new targets do not depend on proprietary libraries.
> * Tier 3 targets should attempt to implement as much of the standard libraries as possible and appropriate (core for most targets, alloc for targets that can support dynamic memory allocation, std for targets with an operating system or equivalent layer of system-provided functionality), but may leave some code unimplemented (either unavailable or stubbed out as appropriate), whether because the target makes it impossible to implement or challenging to implement. The authors of pull requests are not obligated to avoid calling any portions of the standard library on the basis of a tier 3 target not implementing those portions.
This new target implements as much of the standard library as the other tvOS targets do.
> * The target must provide documentation for the Rust community explaining how to build for the target, using cross-compilation if possible. If the target supports running binaries, or running tests (even if they do not pass), the documentation must explain how to run such binaries or tests for the target, using emulation if possible or dedicated hardware if necessary.
I have added the target to the other tvOS targets in [`src/doc/rustc/src/platform-support/apple-tvos.md`](4ab4d48ee5/src/doc/rustc/src/platform-support/apple-tvos.md)
> * Neither this policy nor any decisions made regarding targets shall create any binding agreement or estoppel by any party. If any member of an approving Rust team serves as one of the maintainers of a target, or has any legal or employment requirement (explicit or implicit) that might affect their decisions regarding a target, they must recuse themselves from any approval decisions regarding the target's tier status, though they may otherwise participate in discussions.
> * This requirement does not prevent part or all of this policy from being cited in an explicit contract or work agreement (e.g. to implement or maintain support for a target). This requirement exists to ensure that a developer or team responsible for reviewing and approving a target does not face any legal threats or obligations that would prevent them from freely exercising their judgment in such approval, even if such judgment involves subjective matters or goes beyond the letter of these requirements.
> * Tier 3 targets must not impose burden on the authors of pull requests, or other developers in the community, to maintain the target. In particular, do not post comments (automated or manual) on a PR that derail or suggest a block on the PR based on a tier 3 target. Do not send automated messages or notifications (via any medium, including via ``@)`` to a PR author or others involved with a PR regarding a tier 3 target, unless they have opted into such messages.
> * Backlinks such as those generated by the issue/PR tracker when linking to an issue or PR are not considered a violation of this policy, within reason. However, such messages (even on a separate repository) must not generate notifications to anyone involved with a PR who has not requested such notifications.
> * Patches adding or updating tier 3 targets must not break any existing tier 2 or tier 1 target, and must not knowingly break another tier 3 target without approval of either the compiler team or the maintainers of the other tier 3 target.
> * In particular, this may come up when working on closely related targets, such as variations of the same architecture with different features. Avoid introducing unconditional uses of features that another variation of the target may not have; use conditional compilation or runtime detection, as appropriate, to let each target run code supported by that target.
I acknowledge these requirements and intend to ensure that they are met.
This target does not touch any existing tier 2 or tier 1 targets and should not break any other targets.
This triggers a consistency check in rust (that all linker flavours
must have identical arguments), and on NetBSD/i386, the 32-bitness
is implicitly chosen through the chosen toolchain, and appears to
not be required. So drop it, and also drop the imports of the
now-no-longer-used identifiers.
Allow target specs to use an LLD flavor, and self-contained linking components
This PR allows:
- target specs to use an LLD linker-flavor: this is needed to switch `x86_64-unknown-linux-gnu` to using LLD, and is currently not possible because the current flavor json serialization fails to roundtrip on the modern linker-flavors. This can e.g. be seen in https://github.com/rust-lang/rust/pull/115622#discussion_r1321312880 which explains where an `Lld::Yes` is ultimately deserialized into an `Lld::No`.
- target specs to declare self-contained linking components: this is needed to switch `x86_64-unknown-linux-gnu` to using `rust-lld`
- adds an end-to-end test of a custom target json simulating `x86_64-unknown-linux-gnu` being switched to using `rust-lld`
- disables codegen backends from participating because they don't support `-Zgcc-ld=lld` which is the basis of mcp510.
r? `@petrochenkov:` if the approach discussed https://github.com/rust-lang/rust/pull/115622#discussion_r1329403467 and on zulip would work for you: basically, see if we can emit only modern linker flavors in the json specs, but accept both old and new flavors while reading them, to fix the roundtrip issue.
The backwards compatible `LinkSelfContainedDefault` variants are still serialized and deserialized in `crt-objects-fallback`, while the spec equivalent of e.g. `-Clink-self-contained=+linker` is serialized into a different json object (with future-proofing to incorporate `crt-objects-fallback` in the future).
---
I've been test-driving this in https://github.com/rust-lang/rust/pull/113382 to test actually switching `x86_64-unknown-linux-gnu` to `rust-lld` (and fix what needs to be fixed in CI, bootstrap, etc), and it seems to work fine.
This restricts instructions to those offered by Pentium,
to support e.g. AMD Geode.
There is already an entry for this target in the NetBSD
platform support page at
src/doc/rustc/src/platform-support/netbsd.md
...so this should forestall its removal.
Additional fixes are needed for some vendored modules, this
is the changes in the rust compiler core itself.
Removes the backwards-compatible `LinkSelfContainedDefault`, by
incorporating the remaining specifics into `LinkSelfContained`.
Then renames the modern options to keep the old name.
this ensures roundtripping of stable and unstable values:
- backwards-compatible values can be deserialized, as well as the new
unstable values
- unstable values are serialized.
