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Windows arm64: use cc-rs' prefer_clang_cl_over_msvc #2699

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Windows arm64: use cc-rs' prefer_clang_cl_over_msvc #2699

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Windows arm64: use cc-rs' prefer_clang_cl_over_msvc
dennisameling Sep 6, 2025
27e2b2d
Cleanup
dennisameling Sep 6, 2025
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8 changes: 0 additions & 8 deletions .github/workflows/ci.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -143,9 +143,6 @@ jobs:

- run: rustup toolchain install --no-self-update --profile=minimal 1.66.0

- run: echo "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\Llvm\x64\bin" >> $GITHUB_PATH
shell: bash

- run: sh mk/package.sh
shell: bash

Expand Down Expand Up @@ -483,11 +480,6 @@ jobs:
- if: ${{ contains(matrix.host_os, 'windows') && contains(matrix.target, '86') }}
run: ./mk/install-build-tools.ps1

- if: ${{ matrix.target == 'aarch64-pc-windows-msvc' && !contains(matrix.host_os, 'arm') }}
run: |
echo "C:\Program Files (x86)\Microsoft Visual Studio\2022\Enterprise\VC\Tools\Llvm\x64\bin" >> $GITHUB_PATH
shell: bash

- if: ${{ !contains(matrix.host_os, 'windows') }}
run: |
mk/cargo.sh +${{ matrix.rust_channel }} test --lib --tests -vv --target=${{ matrix.target }} ${{ matrix.cargo_options }} ${{ matrix.features }} ${{ matrix.mode }} ${{ matrix.cargo_test_options }}
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13 changes: 0 additions & 13 deletions BUILDING.md
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Expand Up @@ -25,19 +25,6 @@ supported.

For Windows ARM64 targets (aarch64-pc-windows-msvc), the Visual Studio Build
Tools “VS 2022 C++ ARM64 build tools” and "clang" components must be installed.
Add Microsoft's provided version of `clang` to `%PATH%`, which will allow the
build to work in GitHub Actions without installing anything:
```
$env:Path += ";C:\Program Files (x86)\Microsoft Visual Studio\2022\Enterprise\VC\Tools\Llvm\x64\bin"
```
If you (locally) have “Build Tools for Visual Studio 2022” instead, use:
```
$env:Path += ";C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\VC\Tools\Llvm\x64\bin"
```
Alternatively, if the host machine is already a Windows ARM64 then use:
```
$env:Path += ";C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\Llvm\ARM64\bin"
```

Packaged Builds
---------------
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11 changes: 9 additions & 2 deletions Cargo.lock
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2 changes: 1 addition & 1 deletion Cargo.toml
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Expand Up @@ -172,7 +172,7 @@ wasm-bindgen-test = { version = "0.3.37", default-features = false, features = [
libc = { version = "0.2.172", default-features = false }

[build-dependencies]
cc = { version = "1.2.8", default-features = false }
cc = { version = "1.2.36", default-features = false }

[features]
# These features are documented in the top-level module's documentation.
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13 changes: 5 additions & 8 deletions build.rs
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Expand Up @@ -188,7 +188,6 @@ fn cpp_flags(compiler: &cc::Tool) -> &'static [&'static str] {
"/Zc:forScope",
"/Zc:inline",
// Warnings.
"/Wall",
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@dennisameling dennisameling Sep 6, 2025 •
edited
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This seems to be triggering the warnings (which are then treated as errors) that @MarijnS95 reported here. Even when adding /std:c11, they keep showing up:

warning: [email protected]: In file included from C:\repos\ring\crypto/curve25519/curve25519.c:22:
warning: [email protected]: In file included from C:\repos\ring\crypto/curve25519\internal.h:18:
warning: [email protected]: C:\repos\ring\include\ring-core/base.h(60,1): error: '_Static_assert' is incompatible with C standards before C11 [-Werror,-Wpre-c11-compat]
warning: [email protected]:    60 | OPENSSL_STATIC_ASSERT(sizeof(int32_t) == sizeof(int), "int isn't 32 bits.");
warning: [email protected]:       | ^
warning: [email protected]: C:\repos\ring\include\ring-core/type_check.h(29,42): note: expanded from macro 'OPENSSL_STATIC_ASSERT'
warning: [email protected]:    29 | #define OPENSSL_STATIC_ASSERT(cond, msg) _Static_assert(cond, msg)
warning: [email protected]:       |                                          ^
warning: [email protected]: In file included from C:\repos\ring\crypto/curve25519/curve25519.c:22:
warning: [email protected]: In file included from C:\repos\ring\crypto/curve25519\internal.h:18:
warning: [email protected]: C:\repos\ring\include\ring-core/base.h(61,1): error: '_Static_assert' is incompatible with C standards before C11 [-Werror,-Wpre-c11-compat]
warning: [email protected]:    61 | OPENSSL_STATIC_ASSERT(sizeof(uint32_t) == sizeof(unsigned int), "unsigned int isn't 32 bits.");
warning: [email protected]:       | ^
warning: [email protected]: C:\repos\ring\include\ring-core/type_check.h(29,42): note: expanded from macro 'OPENSSL_STATIC_ASSERT'
warning: [email protected]:    29 | #define OPENSSL_STATIC_ASSERT(cond, msg) _Static_assert(cond, msg)
warning: [email protected]:       |                                          ^
warning: [email protected]: In file included from C:\repos\ring\crypto/curve25519/curve25519.c:22:
warning: [email protected]: In file included from C:\repos\ring\crypto/curve25519\internal.h:18:
warning: [email protected]: C:\repos\ring\include\ring-core/base.h(62,1): error: '_Static_assert' is incompatible with C standards before C11 [-Werror,-Wpre-c11-compat]
warning: [email protected]:    62 | OPENSSL_STATIC_ASSERT(sizeof(size_t) == sizeof(uintptr_t), "uintptr_t and size_t differ.");
warning: [email protected]:       | ^
warning: [email protected]: C:\repos\ring\include\ring-core/type_check.h(29,42): note: expanded from macro 'OPENSSL_STATIC_ASSERT'
warning: [email protected]:    29 | #define OPENSSL_STATIC_ASSERT(cond, msg) _Static_assert(cond, msg)
warning: [email protected]:       |                                          ^

Removing the /Wall flag fixes the build. This looks like a bug in clang-cl.exe to me and I could reproduce the behavior in a minimal example. Reported that here: https://developercommunity.visualstudio.com/t/Calling-clang-clexe-with-Wall-reports/10961806

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@dragonmux dragonmux Oct 15, 2025

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This is not a bug in clang-cl - /Wall in CL parlance translates to -Weverything in Clang parlance. That includes these spurious warnings designed to help users migrating code forward to avoid pitfalls when their code base uses multiple C versions simultaneously.

"/wd4127", // C4127: conditional expression is constant
"/wd4464", // C4464: relative include path contains '..'
"/wd4514", // C4514: <name>: unreferenced inline function has be
Expand Down Expand Up @@ -591,13 +590,11 @@ fn obj_path(out_dir: &Path, src: &Path) -> PathBuf {

fn configure_cc(c: &mut cc::Build, target: &Target, c_root_dir: &Path, include_dir: &Path) {
let compiler = c.get_compiler();
// FIXME: On Windows AArch64 we currently must use Clang to compile C code
let compiler = if target.os == WINDOWS && target.arch == AARCH64 && !compiler.is_like_clang() {
let _ = c.compiler("clang");
c.get_compiler()
} else {
compiler
};
// On Windows AArch64 we currently must use Clang to compile C code.
// clang-cl.exe has support for MSVC-style command-line arguments.
if target.os == WINDOWS && target.arch == AARCH64 && !compiler.is_like_clang() {
c.prefer_clang_cl_over_msvc(true);
}

let _ = c.include(c_root_dir.join("include"));
let _ = c.include(include_dir);
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2 changes: 1 addition & 1 deletion mk/package.sh
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Expand Up @@ -11,7 +11,7 @@ fi

msrv=1.66.0
cargo clean --target-dir=target/pregenerate_asm
RING_PREGENERATE_ASM=1 CC_AARCH64_PC_WINDOWS_MSVC=clang \
RING_PREGENERATE_ASM=1 \
cargo +${msrv} build -p ring --target-dir=target/pregenerate_asm
if [[ -n "$(git status --porcelain -- ':(exclude)pregenerated/')" ]]; then
echo Repository is dirty.
Expand Down