fix: use build.rustflags config to avoid SIGILL in build scripts (#90)

RUSTFLAGS applies to all rustc invocations including build scripts.
When targeting x86-64-v4 (AVX-512), the libz-sys build script was
compiled with AVX-512 instructions and crashed on CI runners that
lack AVX-512 support. Switch to cargo --config build.rustflags which
only applies to target crate compilation, not host build scripts.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ewels

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
             os: ubuntu-latest
           - name: linux-x86_64-v3
             os: ubuntu-latest
-            rustflags: "-C target-cpu=x86-64-v3"
+            target_cpu: x86-64-v3
           - name: macos-aarch64
             os: macos-latest
     steps:
@@ -46,14 +46,18 @@ jobs:
       - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # ratchet:Swatinem/rust-cache@v2.9.1
 
       - name: Build
-        run: cargo build --release
+        run: >
+          cargo build --release
+          ${TARGET_CPU:+--config "build.rustflags=['-C', 'target-cpu=$TARGET_CPU']"}
         env:
-          RUSTFLAGS: ${{ matrix.rustflags || '' }}
+          TARGET_CPU: ${{ matrix.target_cpu || '' }}
 
       - name: Test
-        run: cargo test --release
+        run: >
+          cargo test --release
+          ${TARGET_CPU:+--config "build.rustflags=['-C', 'target-cpu=$TARGET_CPU']"}
         env:
-          RUSTFLAGS: ${{ matrix.rustflags || '' }}
+          TARGET_CPU: ${{ matrix.target_cpu || '' }}
 
   fmt:
     name: Formatting

.github/workflows/release.yml

@@ -65,13 +65,13 @@ jobs:
           - name: linux-x86_64-v3
             os: ubuntu-latest
             target: x86_64-unknown-linux-gnu
-            rustflags: "-C target-cpu=x86-64-v3"
+            target_cpu: x86-64-v3
 
           # Linux x86_64 with AVX-512 (x86-64-v4)
           - name: linux-x86_64-v4
             os: ubuntu-latest
             target: x86_64-unknown-linux-gnu
-            rustflags: "-C target-cpu=x86-64-v4"
+            target_cpu: x86-64-v4
 
           # Linux aarch64 (native arm64 runner, baseline)
           - name: linux-aarch64
@@ -82,7 +82,7 @@ jobs:
           - name: linux-aarch64-neoverse-v1
             os: ubuntu-24.04-arm
             target: aarch64-unknown-linux-gnu
-            rustflags: "-C target-cpu=neoverse-v1"
+            target_cpu: neoverse-v1
 
           # macOS x86_64 (cross-compiled on Apple Silicon runner)
           - name: macos-x86_64
@@ -98,7 +98,7 @@ jobs:
           - name: macos-aarch64-apple-m1
             os: macos-latest
             target: aarch64-apple-darwin
-            rustflags: "-C target-cpu=apple-m1"
+            target_cpu: apple-m1
 
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # ratchet:actions/checkout@v6.0.2
@@ -122,9 +122,11 @@ jobs:
         run: brew install bzip2 xz
 
       - name: Build
-        run: cargo build --release --target ${{ matrix.target }}
+        run: >
+          cargo build --release --target ${{ matrix.target }}
+          ${TARGET_CPU:+--config "build.rustflags=['-C', 'target-cpu=$TARGET_CPU']"}
         env:
-          RUSTFLAGS: ${{ matrix.rustflags || '' }}
+          TARGET_CPU: ${{ matrix.target_cpu || '' }}
 
       - name: Package
         id: package

Dockerfile

@@ -21,9 +21,10 @@ COPY Cargo.toml Cargo.lock build.rs ./
 COPY cpp/ cpp/
 COPY src/ src/
 
-RUN RUSTFLAGS="${CPU_TARGET:+-C target-cpu=$CPU_TARGET}" \
-    GIT_SHORT_HASH="${GIT_SHORT_HASH}" \
-    cargo build --release && strip target/release/rustqc
+RUN GIT_SHORT_HASH="${GIT_SHORT_HASH}" \
+    cargo build --release \
+        ${CPU_TARGET:+--config "build.rustflags=['-C', 'target-cpu=$CPU_TARGET']"} \
+    && strip target/release/rustqc
 
 # ---- Runtime stage ----
 FROM debian:bookworm-slim