Add arm64ec-pc-windows-msvc target

[dpaoliello]

Introduces the arm64ec-pc-windows-msvc target for building Arm64EC ("Emulation Compatible") binaries for Windows.

For more information about Arm64EC see https://learn.microsoft.com/en-us/windows/arm/arm64ec.

---

Release Notes

Adding support for Arm64EC does not need to be added to the release notes, however this change bumps the version of cc-rs that Rust is using from 1.0.79 to 1.0.90, which affects how the Rust compiler finds the linker to use for MSVC targets:

• Better detection for MSVC tooling to use if there is no default set: Detect msvc version if there is no default cc-rs#696
• Use ARM64 MSVC on ARM64 Windows, and prefer falling back to x64 tooling if x64 emulation is available: Support native ARM64 MSVC toolchain, and fallback to x64 if emulation is available cc-rs#957
• MSVC tooling can be used on non-Windows hosts by setting the VSINSTALLDIR environment variable: Support finding Windows tools on non-Windows host cc-rs#907
• MSVC tooling from Visual Studio 2012 (v11) will no longer be used: Drop support for Visual Studio 11 (2012) cc-rs#981

---

Tier 3 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 maintainer for this target.

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 uses the arm64ec architecture to match LLVM and MSVC, and the -pc-windows-msvc suffix to indicate that it targets Windows via the MSVC environment.

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.

Target name exactly specifies the type of code that will be produced.

If possible, use only letters, numbers, dashes and underscores for the name. Periods (.) are known to cause issues in Cargo.

Done.

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The target must not introduce license incompatibilities.

Uses the same dependencies, requirements and licensing as the other *-pc-windows-msvc targets.

Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).

Understood.

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Uses the same dependencies, requirements and licensing as the other *-pc-windows-msvc targets.

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.

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Understood, I am not a member of the 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.

Both core and alloc are supported.

Support for std depends on making changes to the standard library, stdarch and backtrace which cannot be done yet as they require fixes coming in LLVM 18.

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Documentation is provided in src/doc/rustc/src/platform-support/arm64ec-pc-windows-msvc.md

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Understood.

[rustbot]

r? @b-naber

(rustbot has picked a reviewer for you, use r? to override)

[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

[dpaoliello]

r? compiler-team

[Urgau]

Support for std dependends on making changes to the standard library, stdarch and backtrace which cannot be done yet as the bootstrapping compiler raises a warning ("unexpected cfg condition value") for target_arch = "arm64ec".

You can add "extra check-cfg" values with the EXTRA_CHECK_CFG bootstrap list, something like this should do it:

-    (Some(Mode::Std), "target_arch", Some(&["spirv", "nvptx", "xtensa"])),
+    // #[cfg(bootstrap)] arm64ec
+    (Some(Mode::Std), "target_arch", Some(&["spirv", "nvptx", "xtensa", "arm64ec"])),

You will also need to bless the tests output of some UI tests (./x.py test --stage 1 tests/ui/ --bless)

[dpaoliello]

FYI, CI failures are caused by rust-lang/cc-rs#913

[petrochenkov]

Marking as blocked on the PRs linked above (https://github.com/rust-lang/rust/pull/119199/files#r1434435847, https://github.com/rust-lang/rust/pull/119199/files#r1434436282).
@rustbot blocked

[rustbot]

Some changes occurred in src/tools/cargo

cc @ehuss

[workingjubilee]

cc-rs has had 11 patch versions since it was last bumped and its functionality or lack thereof causes issues for toolchain support for platforms, not just this one, therefore

@bors p=11 rollup=never

[bors]

⌛ Testing commit a6a556c with merge 9c3ad80...

[bors]

☀️ Test successful - checks-actions
Approved by: petrochenkov
Pushing 9c3ad80 to master...

[rust-timer]

Finished benchmarking commit (9c3ad80): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.6%	[2.6%, 2.6%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.6%	[2.6%, 2.6%]	1

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 647.318s -> 647.485s (0.03%)
Artifact size: 172.63 MiB -> 172.63 MiB (-0.00%)

[Wyvern]

Try it build with arm64ec-pc-windows-msvc target but got lots of errors like below:

error[: unresolved import `crate::sys::common::alloc::MIN_ALIGN`
  --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\sys\pal\windows\alloc.rs:8:51
   |
8  | use crate::sys::common::alloc::{realloc_fallback, MIN_ALIGN};
   |                                                   ^^^^^^^^^ no `MIN_ALIGN` in `sys::pal::common::alloc`
   |
note: found an item that was configured out
  --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\sys\pal\common\alloc.rs:22:11
   |
22 | pub const MIN_ALIGN: usize = 8;
   |           ^^^^^^^^^
note: found an item that was configured out
  --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\sys\pal\common\alloc.rs:34:11
   |
34 | pub const MIN_ALIGN: usize = 16;
   |           ^^^^^^^^^
note: found an item that was configured out
  --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\sys\pal\common\alloc.rs:40:11
   |
40 | pub const MIN_ALIGN: usize = 4;
   |           ^^^^^^^^^

error[: unresolved import `self::dbghelp::trace`
   --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\..\..\backtrace\src\backtrace\mod.rs:187:13
    |
187 |         use self::dbghelp::trace as trace_imp;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no `trace` in `backtrace_rs::backtrace::dbghelp`
    |
note: found an item that was configured out
   --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\..\..\backtrace\src\backtrace\dbghelp.rs:127:15
    |
127 | pub unsafe fn trace(cb: &mut dyn FnMut(&super::Frame) -> bool) {
    |               ^^^^^
note: found an item that was configured out
   --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\..\..\backtrace\src\backtrace\dbghelp.rs:174:15
    |
174 | pub unsafe fn trace(cb: &mut dyn FnMut(&super::Frame) -> bool) {
    |               ^^^^^

error[: cannot find type `CONTEXT` in this scope
   --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\sys\pal\windows\c.rs:499:33
    |
499 |         pub ContextRecord: *mut CONTEXT,
    |                                 ^^^^^^^ not found in this scope

error[: cannot find type `WSADATA` in this scope
   --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\sys\pal\windows\c.rs:507:63
    |
507 |     pub fn WSAStartup(wversionrequested: u16, lpwsadata: *mut WSADATA) -> i32;
    |                                                               ^^^^^^^ not found in this scope

error[: cannot find type `WSADATA` in module `c`
   --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\sys\pal\windows\net.rs:38:26
    |
38  |         let mut data: c::WSADATA = mem::zeroed();
    |                          ^^^^^^^ not found in `c`
    |
note: found an item that was configured out
   --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\sys\pal\windows\c.rs:511:12
    |
511 | pub struct WSADATA {
    |            ^^^^^^^
    = note: the item is gated behind the `arm` feature

error[: cannot find type `CONTEXT` in this scope
   --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\..\..\backtrace\src\backtrace\dbghelp.rs:61:18
    |
61  | struct MyContext(CONTEXT);
    |                  ^^^^^^^ help: a type alias with a similar name exists: `PCONTEXT`
    |
   ::: /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\..\..\backtrace\src\windows.rs:152:9
    |
152 |         pub type $name = $ty;
    |         --------------------- similarly named type alias `PCONTEXT` defined here

error[: cannot find type `CONTEXT` in this scope
   --> /rustc/9c3ad802d9b9633d60d3a74668eb1be819212d34\library\std\src\..\..\backtrace\src\windows.rs:388:30
    |
152 |         pub type $name = $ty;
    |         --------------------- similarly named type alias `PCONTEXT` defined here
...
388 |     pub type PCONTEXT = *mut CONTEXT;
    |                              ^^^^^^^ help: a type alias with a similar name exists: `PCONTEXT`

any suggestions...?

[dpaoliello]

Try it build with arm64ec-pc-windows-msvc target but got lots of errors like below:

...

any suggestions...?

I'm working on standard library support - note the links above to PRs to compiler-builtins, portable-simd and backtrace. I should have the PR for stdarch out today. Once those are complete, I will be able to submit another PR for the standard library itself (that brings in all of those plus more).

But, for now, this is a no_std target only...

[dpaoliello]

@rustbot label +relnotes

@NobodyXu @ChrisDenton @thomcc @Amanieu - I've tried to find changes to cc-rs that may be relevant to users of the Rust toolchain and summarize them, but I'd appreciate it if you all could check if there's anything that I've missed or misrepresented.

This change bumps the version of cc-rs that Rust is using from 1.0.79 to 1.0.90, which affects how the Rust compiler finds the linker to use for MSVC targets:

• Better detection for MSVC tooling to use if there is no default set: Detect msvc version if there is no default cc-rs#696
• Use ARM64 MSVC on ARM64 Windows, and prefer falling back to x64 tooling if x64 emulation is available: Support native ARM64 MSVC toolchain, and fallback to x64 if emulation is available cc-rs#957
• MSVC tooling can be used on non-Windows hosts by setting the VSINSTALLDIR environment variable: Support finding Windows tools on non-Windows host cc-rs#907
• MSVC tooling from Visual Studio 2012 (v11) will no longer be used: Drop support for Visual Studio 11 (2012) cc-rs#981

[workingjubilee]

@dpaoliello Most users of the toolchain don't have to worry about cc-rs changes, because they are not building rustc but using one of its distributed toolchains. Thus those who are only building rust code for, say, wasm32-unknown-unknown, and thus using their current host, don't have to worry about this at all. However those building rustc for a tier 3 host obviously are impacted!

I think noting somewhat abstractly "we updated one of our major build-time dependencies for rustc, this will only affect you if you're building a fresh compiler" and then focusing on the ones most likely to be a bother for a software distribution's maintainer is probably best.

[dpaoliello]

@dpaoliello Most users of the toolchain don't have to worry about cc-rs changes, because they are not building rustc but using one of its distributed toolchains. Thus those who are only building rust code for, say, wasm32-unknown-unknown, and thus using their current host, don't have to worry about this at all. However those building rustc for a tier 3 host obviously are impacted!

I think noting somewhat abstractly "we updated one of our major build-time dependencies for rustc, this will only affect you if you're building a fresh compiler" and then focusing on the ones most likely to be a bother for a software distribution's maintainer is probably best.

My understanding is that rustc uses cc-rs to find the linker it invokes, so any change to how cc-rs finds the toolchain or configures the linker may affect a user of rustc as well.

[workingjubilee]

@dpaoliello Oh, you are right, but apparently only when compiling for Windows:

rust/compiler/rustc_codegen_ssa/src/back/linker.rs

Line 49 in 74acabe

let msvc_tool = windows_registry::find_tool(sess.opts.target_triple.triple(), "link.exe");

Everything else is hand-rolled, it seems.

[ChrisDenton]

Yes, this tends to be much harder to do on other OSes (also somewhat less necessary), whereas Windows has a COM API installed by Visual Studio which can be queried.

[dpaoliello]

@dpaoliello Oh, you are right, but apparently only when compiling for Windows:

rust/compiler/rustc_codegen_ssa/src/back/linker.rs

Line 49 in 74acabe

let msvc_tool = windows_registry::find_tool(sess.opts.target_triple.triple(), "link.exe");

Everything else is hand-rolled, it seems.

Ah, thanks, didn't realize it was MSVC-only - updated my comment to match and filtered to only the MSVC relevant changes.