Auto merge of #118150 - roblabla:new-win7-targets, r=davidtwco

Add new targets {x86_64,i686}-win7-windows-msvc

This PR adds two new Tier 3 targets, x86_64-win7-windows-msvc and i686-win7-windows-msvc, that aim to support targeting Windows 7 after the `*-pc-windows-msvc` target drops support for it (slated to happen in 1.76.0).

# 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 proposed new tier 3 target must be reviewed and approved by a member of the compiler team based on these requirements. The reviewer may choose to gauge broader compiler team consensus via a [Major Change Proposal (MCP)](https://forge.rust-lang.org/compiler/mcp.html).
>
> A proposed target or target-specific patch that substantially changes code shared with other targets (not just target-specific code) must be reviewed and approved by the appropriate team for that shared code before acceptance.
>
>  - 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.)

This is me, `@roblabla` on github.

> - 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.

I went with naming the target `x86_64-win7-windows-msvc`, inserting the `win7` in the vendor field (usually set to to `pc`). This is done to avoid ecosystem churn, as quite a few crates have `cfg(target_os = "windows")` or `cfg(target_env = "msvc")`, but nearly no `cfg(target_vendor = "pc")`. Since my goal is to be able to seamlessly swap to the `win7` target, I figured it'd be easier this way.

>  - 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.

I believe the naming is pretty explicit.

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

The name comforms to this requirement.

> - 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.

As far as I understand it, this target has exactly the same legal situation as the existing Tier 1 x86_64-pc-windows-msvc.

> - 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.

> - 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 target supports the whole libstd surface, since it's essentially reusing all of the x86_64-pc-windows-msvc target. Understood.

> - 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.

Wrote some documentation on how to build, test and cross-compile the target in the `platform-support` part. Hopefully it's enough to get started.

> - 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.

Understood.

> If a tier 3 target stops meeting these requirements, or the target maintainers no longer have interest or time, or the target shows no signs of activity and has not built for some time, or removing the target would improve the quality of the Rust codebase, we may post a PR to remove it; any such PR will be CCed to the target maintainers (and potentially other people who have previously worked on the target), to check potential interest in improving the situation.

Understood.

compiler/rustc_target/src/spec/mod.rs

@@ -1603,8 +1603,10 @@ fn $module() {
     ("aarch64-uwp-windows-msvc", aarch64_uwp_windows_msvc),
     ("x86_64-pc-windows-msvc", x86_64_pc_windows_msvc),
     ("x86_64-uwp-windows-msvc", x86_64_uwp_windows_msvc),
+    ("x86_64-win7-windows-msvc", x86_64_win7_windows_msvc),
     ("i686-pc-windows-msvc", i686_pc_windows_msvc),
     ("i686-uwp-windows-msvc", i686_uwp_windows_msvc),
+    ("i686-win7-windows-msvc", i686_win7_windows_msvc),
     ("i586-pc-windows-msvc", i586_pc_windows_msvc),
     ("thumbv7a-pc-windows-msvc", thumbv7a_pc_windows_msvc),
     ("thumbv7a-uwp-windows-msvc", thumbv7a_uwp_windows_msvc),

compiler/rustc_target/src/spec/targets/i686_win7_windows_msvc.rs

@@ -0,0 +1,32 @@
+use crate::spec::{base, LinkerFlavor, Lld, Target};
+
+pub fn target() -> Target {
+    let mut base = base::windows_msvc::opts();
+    base.cpu = "pentium4".into();
+    base.max_atomic_width = Some(64);
+
+    base.add_pre_link_args(
+        LinkerFlavor::Msvc(Lld::No),
+        &[
+            // Mark all dynamic libraries and executables as compatible with the larger 4GiB address
+            // space available to x86 Windows binaries on x86_64.
+            "/LARGEADDRESSAWARE",
+            // Ensure the linker will only produce an image if it can also produce a table of
+            // the image's safe exception handlers.
+            // https://docs.microsoft.com/en-us/cpp/build/reference/safeseh-image-has-safe-exception-handlers
+            "/SAFESEH",
+        ],
+    );
+    // Workaround for #95429
+    base.has_thread_local = false;
+
+    Target {
+        llvm_target: "i686-pc-windows-msvc".into(),
+        pointer_width: 32,
+        data_layout: "e-m:x-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
+            i64:64-f80:128-n8:16:32-a:0:32-S32"
+            .into(),
+        arch: "x86".into(),
+        options: base,
+    }
+}

compiler/rustc_target/src/spec/targets/x86_64_win7_windows_msvc.rs

@@ -0,0 +1,18 @@
+use crate::spec::{base, Target};
+
+pub fn target() -> Target {
+    let mut base = base::windows_msvc::opts();
+    base.cpu = "x86-64".into();
+    base.plt_by_default = false;
+    base.max_atomic_width = Some(64);
+    base.vendor = "win7".into();
+
+    Target {
+        llvm_target: "x86_64-win7-windows-msvc".into(),
+        pointer_width: 64,
+        data_layout: "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+            .into(),
+        arch: "x86_64".into(),
+        options: base,
+    }
+}

src/doc/rustc/src/SUMMARY.md

@@ -56,6 +56,7 @@
     - [\*-unknown-uefi](platform-support/unknown-uefi.md)
     - [wasm32-wasi-preview1-threads](platform-support/wasm32-wasi-preview1-threads.md)
     - [wasm64-unknown-unknown](platform-support/wasm64-unknown-unknown.md)
+    - [\*-win7-windows-msvc](platform-support/win7-windows-msvc.md)
     - [x86_64-fortanix-unknown-sgx](platform-support/x86_64-fortanix-unknown-sgx.md)
     - [x86_64-unknown-none](platform-support/x86_64-unknown-none.md)
     - [x86_64h-apple-darwin](platform-support/x86_64h-apple-darwin.md)

src/doc/rustc/src/platform-support.md

@@ -276,6 +276,7 @@ target | std | host | notes
 [`i686-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 32-bit OpenBSD [^x86_32-floats-return-ABI]
 `i686-uwp-windows-gnu` | ? |  | [^x86_32-floats-return-ABI]
 `i686-uwp-windows-msvc` | ? |  | [^x86_32-floats-return-ABI]
+[`i686-win7-windows-msvc`](platform-support/win7-windows-msvc.md) | ✓ |   | 32-bit Windows 7 support [^x86_32-floats-return-ABI]
 `i686-wrs-vxworks` | ? |  | [^x86_32-floats-return-ABI]
 [`m68k-unknown-linux-gnu`](platform-support/m68k-unknown-linux-gnu.md) | ? |  | Motorola 680x0 Linux
 `mips-unknown-linux-gnu` | ✓ | ✓ | MIPS Linux (kernel 4.4, glibc 2.23)
@@ -352,6 +353,7 @@ target | std | host | notes
 [`x86_64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 64-bit OpenBSD
 `x86_64-uwp-windows-gnu` | ✓ |  |
 `x86_64-uwp-windows-msvc` | ✓ |  |
+[`x86_64-win7-windows-msvc`](platform-support/win7-windows-msvc.md) | ✓ |   | 64-bit Windows 7 support
 `x86_64-wrs-vxworks` | ? |  |
 [`x86_64h-apple-darwin`](platform-support/x86_64h-apple-darwin.md) | ✓ | ✓ | macOS with late-gen Intel (at least Haswell)
 

src/doc/rustc/src/platform-support/win7-windows-msvc.md

@@ -0,0 +1,80 @@
+# *-win7-windows-msvc
+
+**Tier: 3**
+
+Windows targets continuing support of windows7.
+
+## Target maintainers
+
+- @roblabla
+
+## Requirements
+
+This target supports all of core, alloc, std and test. This is automatically
+tested every night on private infrastructure hosted by the maintainer. Host
+tools may also work, though those are not currently tested.
+
+Those targets follow Windows calling convention for extern "C".
+
+Like any other Windows target, the created binaries are in PE format.
+
+## Building the target
+
+You can build Rust with support for the targets by adding it to the target list in config.toml:
+
+```toml
+[build]
+build-stage = 1
+target = [ "x86_64-win7-windows-msvc" ]
+```
+
+## Building Rust programs
+
+Rust does not ship pre-compiled artifacts for this target. To compile for this
+target, you will either need to build Rust with the target enabled (see
+"Building the target" above), or build your own copy by using `build-std` or
+similar.
+
+## Testing
+
+Created binaries work fine on Windows or Wine using native hardware. Remote
+testing is possible using the `remote-test-server` described [here](https://rustc-dev-guide.rust-lang.org/tests/running.html#running-tests-on-a-remote-machine).
+
+## Cross-compilation toolchains and C code
+
+Compatible C code can be built with either MSVC's `cl.exe` or LLVM's clang-cl.
+
+Cross-compilation is possible using clang-cl/lld-link. It also requires the
+Windows SDK, which can be acquired using [`xwin`](https://github.com/Jake-Shadle/xwin).
+
+- Install `clang-cl` and `lld-link` on your machine, and make sure they are in
+  your $PATH.
+- Install `xwin`: `cargo install xwin`
+- Use `xwin` to install the Windows SDK: `xwin splat --output winsdk`
+- Create an `xwin-lld-link` script with the following content:
+
+  ```bash
+  #!/usr/bin/env bash
+  set -e
+  XWIN=/path/to/winsdk
+  lld-link "$@" /libpath:$XWIN/crt/lib/x86_64 /libpath:$XWIN/sdk/lib/um/x86_64 /libpath:$XWIN/sdk/lib/ucrt/x86_64
+  ```
+
+- Create an `xwin-clang-cl` script with the following content:
+
+  ```bash
+  #!/usr/bin/env bash
+  set -e
+  XWIN=/path/to/winsdk
+  clang-cl /imsvc "$XWIN/crt/include" /imsvc "$XWIN/sdk/include/ucrt" /imsvc "$XWIN/sdk/include/um" /imsvc "$XWIN/sdk/include/shared" --target="x86_64-pc-windows-msvc" "$@"
+  ```
+
+- In your config.toml, add the following lines:
+
+  ```toml
+  [target.x86_64-win7-windows-msvc]
+  linker = "path/to/xwin-lld-link"
+  cc = "path/to/xwin-clang-cl"
+  ```
+
+You should now be able to cross-compile the Rust std, and any rust program.