diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index 2b1b15e84..b997a4e55 100644
--- a/.github/workflows/main.yaml
+++ b/.github/workflows/main.yaml
@@ -6,7 +6,7 @@ on:
 
 concurrency:
   # Make sure that new pushes cancel running jobs
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.sha }}
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
   cancel-in-progress: true
 
 env:
@@ -59,61 +59,61 @@ jobs:
       fail-fast: false
       matrix:
         include:
-        - target: aarch64-apple-darwin
-          os: macos-26
-        - target: aarch64-unknown-linux-gnu
-          os: ubuntu-26.04-arm
-        - target: aarch64-pc-windows-msvc
-          os: windows-11-vs2026-arm
-        - target: arm-unknown-linux-gnueabi
-          os: ubuntu-26.04
-        - target: arm-unknown-linux-gnueabihf
-          os: ubuntu-26.04
-        - target: armv7-unknown-linux-gnueabihf
-          os: ubuntu-26.04
-        - target: i586-unknown-linux-gnu
-          os: ubuntu-26.04
-        - target: i686-unknown-linux-gnu
-          os: ubuntu-26.04
-        - target: loongarch64-unknown-linux-gnu
-          os: ubuntu-26.04
-        - target: powerpc-unknown-linux-gnu
-          os: ubuntu-26.04
-        - target: powerpc64-unknown-linux-gnu
-          os: ubuntu-26.04
-        - target: powerpc64-unknown-linux-musl
-          os: ["self-hosted", "linux", "powerpc64", "musl"]
-        - target: powerpc64le-unknown-linux-gnu
-          os: ubuntu-26.04
-        - target: powerpc64le-unknown-linux-gnu
-          os: ubuntu-24.04-ppc64le
-        # FIXME(ci): re-enable these once more capacity is avialable
+        # - target: aarch64-apple-darwin
+        #   os: macos-26
+        # - target: aarch64-unknown-linux-gnu
+        #   os: ubuntu-26.04-arm
+        # - target: aarch64-pc-windows-msvc
+        #   os: windows-11-vs2026-arm
+        # - target: arm-unknown-linux-gnueabi
+        #   os: ubuntu-26.04
+        # - target: arm-unknown-linux-gnueabihf
+        #   os: ubuntu-26.04
+        # - target: armv7-unknown-linux-gnueabihf
+        #   os: ubuntu-26.04
+        # - target: i586-unknown-linux-gnu
+        #   os: ubuntu-26.04
+        # - target: i686-unknown-linux-gnu
+        #   os: ubuntu-26.04
+        # - target: loongarch64-unknown-linux-gnu
+        #   os: ubuntu-26.04
+        # - target: powerpc-unknown-linux-gnu
+        #   os: ubuntu-26.04
+        # - target: powerpc64-unknown-linux-gnu
+        #   os: ubuntu-26.04
+        # - target: powerpc64-unknown-linux-musl
+        #   os: ["self-hosted", "linux", "powerpc64", "musl"]
+        # - target: powerpc64le-unknown-linux-gnu
+        #   os: ubuntu-26.04
+        # - target: powerpc64le-unknown-linux-gnu
+        #   os: ubuntu-24.04-ppc64le
+        # # FIXME(ci): re-enable these once more capacity is avialable
+        # # - target: riscv64gc-unknown-linux-gnu
+        # #   os: ["self-hosted", "linux", "riscv64"]
         # - target: riscv64gc-unknown-linux-gnu
-        #   os: ["self-hosted", "linux", "riscv64"]
-        - target: riscv64gc-unknown-linux-gnu
-          os: ubuntu-26.04
-        - target: s390x-unknown-linux-gnu
-          os: self-hosted-linux-s390x-resolute-large-rust # resolute == ubuntu-26.04
-        - target: s390x-unknown-linux-gnu
-          os: ubuntu-24.04-s390x
-        - target: thumbv6m-none-eabi
-          os: ubuntu-26.04
-        - target: thumbv7em-none-eabi
-          os: ubuntu-26.04
-        - target: thumbv7em-none-eabihf
-          os: ubuntu-26.04
-        - target: thumbv7m-none-eabi
-          os: ubuntu-26.04
-        - target: wasm32-unknown-unknown
-          os: ubuntu-26.04
-        - target: x86_64-unknown-linux-gnu
-          os: ubuntu-26.04
-        - target: x86_64-apple-darwin
-          os: macos-26-intel
-        - target: i686-pc-windows-msvc
-          os: windows-2025-vs2026
-        - target: x86_64-pc-windows-msvc
-          os: windows-2025-vs2026
+        #   os: ubuntu-26.04
+        # - target: s390x-unknown-linux-gnu
+        #   os: self-hosted-linux-s390x-resolute-large-rust # resolute == ubuntu-26.04
+        # - target: s390x-unknown-linux-gnu
+        #   os: ubuntu-24.04-s390x
+        # - target: thumbv6m-none-eabi
+        #   os: ubuntu-26.04
+        # - target: thumbv7em-none-eabi
+        #   os: ubuntu-26.04
+        # - target: thumbv7em-none-eabihf
+        #   os: ubuntu-26.04
+        # - target: thumbv7m-none-eabi
+        #   os: ubuntu-26.04
+        # - target: wasm32-unknown-unknown
+        #   os: ubuntu-26.04
+        # - target: x86_64-unknown-linux-gnu
+        #   os: ubuntu-26.04
+        # - target: x86_64-apple-darwin
+        #   os: macos-26-intel
+        # - target: i686-pc-windows-msvc
+        #   os: windows-2025-vs2026
+        # - target: x86_64-pc-windows-msvc
+        #   os: windows-2025-vs2026
         - target: i686-pc-windows-gnu
           os: windows-2025-vs2026
           host_toolchain: nightly-x86_64-gnu
@@ -128,6 +128,7 @@ jobs:
       JOB_HOST_TOOLCHAIN: ${{ matrix.host_toolchain }}
       MAY_SKIP_LIBM_CI: ${{ needs.calculate_vars.outputs.may_skip_libm_ci }}
       RUN_IN_DOCKER: ${{ matrix.os == 'ubuntu-26.04' }}
+      CFLAGS: --std=c17
     steps:
     - name: Print runner information
       run: |
@@ -191,6 +192,27 @@ jobs:
         python3 etc/update-api-list.py --check
         cargo test -p update-api-list
 
+    # - uses: msys2/setup-msys2@v2
+    #   if: matrix.os == 'windows-2025'
+    #   with:
+    #     msystem: UCRT64
+    #     update: true
+    #     install: diffutils m4 make # mingw-w64-rustup
+
+    # - name: Setup windows
+    #   if: matrix.os == 'windows-2025'
+    #   # shell: msys2 {0}
+    #   run: |
+    #     ./ci/run-windows.sh ${{ matrix.target }}
+
+    # - name: Run on Windows
+    #   if: matrix.os == 'windows-2025'
+    #   # shell: msys2 {0}
+    #   run: |
+    #     rustc -vV
+    #     rustup show
+    #     ./ci/run.sh ${{ matrix.target }}
+
     # Non-linux tests just use our raw script
     - name: Run locally
       if: ${{ env.RUN_IN_DOCKER != 'true' }}
@@ -203,7 +225,9 @@ jobs:
 
     - name: Print test logs if available
       if: always()
-      run: if [ -f "target/test-log.txt" ]; then cat target/test-log.txt; fi
+      run: |
+        if [ -f "target/test-log.txt" ]; then cat target/test-log.txt; fi
+        find . -name 'config.log' -exec cat {} ';'
 
     # Workaround to keep Docker cache smaller
     # https://github.com/docker/build-push-action/issues/252
@@ -215,6 +239,7 @@ jobs:
         mv /tmp/.buildx-cache-new /tmp/.buildx-cache
 
   clippy:
+    if: false # TODO
     name: Clippy
     runs-on: ubuntu-26.04
     timeout-minutes: 10
@@ -233,6 +258,7 @@ jobs:
     - run: cargo clippy --workspace --all-targets
 
   zizmor:
+    if: false # TODO
     name: Zizmor (Static analysis for GitHub Actions)
     runs-on: ubuntu-26.04
     permissions:
@@ -244,6 +270,7 @@ jobs:
       - uses: zizmorcore/zizmor-action@3dc1ecc9bcb9e94e9b2c709687979e1298497054 # v0.6.2
 
   build-custom:
+    if: false # TODO
     name: Build custom target
     runs-on: ubuntu-26.04
     timeout-minutes: 10
@@ -266,6 +293,7 @@ jobs:
 
   # FIXME: move this target to test job once https://github.com/rust-lang/rust/pull/150138 merged.
   build-thumbv6k:
+    if: false # TODO
     name: Build thumbv6k
     runs-on: ubuntu-26.04
     timeout-minutes: 10
@@ -285,6 +313,7 @@ jobs:
           -Zjson-target-spec
 
   benchmarks:
+    if: false # TODO
     name: Benchmarks
     timeout-minutes: 30
     strategy:
@@ -332,6 +361,7 @@ jobs:
       run: if [ -f "target/test-log.txt" ]; then cat target/test-log.txt; fi
 
   miri:
+    if: false # TODO
     name: Miri
     runs-on: ubuntu-26.04
     timeout-minutes: 10
@@ -346,6 +376,7 @@ jobs:
     - run: ./ci/miri.sh
 
   msrv:
+    if: false # TODO
     name: Check libm MSRV
     runs-on: ubuntu-26.04
     timeout-minutes: 20
@@ -367,6 +398,7 @@ jobs:
         cargo build --manifest-path libm/Cargo.toml
 
   rustfmt:
+    if: false # TODO
     name: Rustfmt
     runs-on: ubuntu-26.04
     timeout-minutes: 10
@@ -378,6 +410,7 @@ jobs:
     - run: cargo fmt -- --check
 
   extensive:
+    if: false # TODO
     name: Extensive tests for ${{ matrix.ty }}
     needs:
       # Wait on `clippy` so we have some confidence that the crate will build
diff --git a/ci/install-test-deps.sh b/ci/install-test-deps.sh
index b64bcf654..65b5fed23 100755
--- a/ci/install-test-deps.sh
+++ b/ci/install-test-deps.sh
@@ -15,6 +15,8 @@ if [ "$target" = "i686-pc-windows-gnu" ]; then
     echo "PATH=$PATH" >> "$GITHUB_ENV"
 fi
 
+
+
 # Some runners (native ppc and s390x, self-hosted) don't have all the dependencies
 # we need, so we need to install them.
 
@@ -46,3 +48,6 @@ fi
 rustup update "$channel" --no-self-update
 rustup default "$channel"
 rustup target add "$target"
+
+# TODO
+rustup component add llvm-tools-preview
diff --git a/ci/run-windows.sh b/ci/run-windows.sh
new file mode 100755
index 000000000..cc8e076d7
--- /dev/null
+++ b/ci/run-windows.sh
@@ -0,0 +1,29 @@
+#!/bin/bash
+
+set -eux
+
+target="$1"
+
+m4 --help
+make --help
+
+echo "$PATH"
+
+curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- \
+    --default-toolchain nightly-x86_64-gnu \
+    --target "$target" \
+    --profile minimal -y
+
+# Wrapper to ease managerment of environments
+pacman --noconfirm -S pactoys
+# Install C toolchain according to `MSYSTEM`
+pacboy --noconfirm -S toolchain
+
+pacman --noconfirm -S mingw-w64-x86_64-toolchain
+
+# maybe only need mingw-w64-x86_64-gcc?
+
+ls ~/
+echo 'export PATH="/c/Users/$USERNAME/.cargo/bin:$PATH"' >> ~/.bash_profile
+
+echo "$PATH"
diff --git a/ci/run.sh b/ci/run.sh
index 22c136e2d..73f829120 100755
--- a/ci/run.sh
+++ b/ci/run.sh
@@ -54,86 +54,86 @@ else
     profile_flag="--profile"
 fi
 
-# Test our implementation
-if [ "${BUILD_ONLY:-}" = "1" ]; then
-    echo "no tests to run for build-only targets"
-else
-    test_builtins=(
-        "${test_runner[@]}"
-        --package builtins-test
-        --target "$target"
-    )
-
-    asgroup "${test_builtins[@]}"
-    asgroup "${test_builtins[@]}" --release
-    asgroup "${test_builtins[@]}" --features c
-    asgroup "${test_builtins[@]}" --features c --release
-    asgroup "${test_builtins[@]}" --benches --release
-    asgroup "${test_builtins[@]}" --no-default-features
-    asgroup "${test_builtins[@]}" --no-default-features --release
-
-    # Validate that having a verbatim path for the target directory works
-    # (trivial to regress using `/` in paths to build artifacts rather than
-    # `Path::join`). MinGW does not currently support these paths.
-    if [[ "$target" = *"windows"* ]] && [[ "$target" != *"gnu"* ]]; then
-        verb_path=$(cmd.exe //C echo \\\\?\\%cd%\\builtins-test\\target2)
-        "${test_builtins[@]}" --target-dir "$verb_path" --features c
-    fi
-fi
-
-
-echo "::group::Run symcheck"
-
-# Ensure there are no duplicate symbols or references to `core` when
-# `compiler-builtins` is built with various features. Symcheck invokes Cargo to
-# build with the arguments we provide it, then validates the built artifacts.
-SYMCHECK_TEST_TARGET="$target" cargo test -p symcheck --release
-symcheck=(cargo run -p symcheck --release)
-symcheck+=(-- --build-and-check --target "$target")
-
-# Executable section checks are meaningless on no-std targets
-[[ "$target" == *"-none"* ]] && symcheck+=(--no-os)
-
-# We only need to check the configurations std may use
-symcheck_cb_args=(-- --package compiler_builtins --features compiler-builtins)
-"${symcheck[@]}" "${symcheck_cb_args[@]}"
-"${symcheck[@]}" "${symcheck_cb_args[@]}" --release
-"${symcheck[@]}" "${symcheck_cb_args[@]}" --features c
-"${symcheck[@]}" "${symcheck_cb_args[@]}" --features c --release
-"${symcheck[@]}" "${symcheck_cb_args[@]}" --no-default-features
-"${symcheck[@]}" "${symcheck_cb_args[@]}" --no-default-features --release
-
-echo "::endgroup"
-
-
-echo "::group::Run intrinsics tests"
-
-run_intrinsics_test() {
-    build_args=(--verbose --manifest-path builtins-test-intrinsics/Cargo.toml)
-    build_args+=("$@")
-
-    # symcheck also checks the results of builtins-test-intrinsics
-    "${symcheck[@]}" -- "${build_args[@]}"
-
-    # FIXME: we get access violations on Windows, our entrypoint may need to
-    # be tweaked.
-    if [ "${BUILD_ONLY:-}" != "1" ] && ! [[ "$target" = *"windows"* ]]; then
-        cargo run --target "$target" "${build_args[@]}"
-    fi
-}
-
-# Verify that we haven't dropped any intrinsics/symbols
-run_intrinsics_test
-run_intrinsics_test --release
-run_intrinsics_test --features c
-run_intrinsics_test --features c --release
-
-# Verify that there are no undefined symbols to `panic` within our
-# implementations
-CARGO_PROFILE_DEV_LTO=true run_intrinsics_test
-CARGO_PROFILE_RELEASE_LTO=true run_intrinsics_test --release
-
-echo "::endgroup"
+# # Test our implementation
+# if [ "${BUILD_ONLY:-}" = "1" ]; then
+#     echo "no tests to run for build-only targets"
+# else
+#     test_builtins=(
+#         "${test_runner[@]}"
+#         --package builtins-test
+#         --target "$target"
+#     )
+
+#     asgroup "${test_builtins[@]}"
+#     asgroup "${test_builtins[@]}" --release
+#     asgroup "${test_builtins[@]}" --features c
+#     asgroup "${test_builtins[@]}" --features c --release
+#     asgroup "${test_builtins[@]}" --benches --release
+#     asgroup "${test_builtins[@]}" --no-default-features
+#     asgroup "${test_builtins[@]}" --no-default-features --release
+
+#     # Validate that having a verbatim path for the target directory works
+#     # (trivial to regress using `/` in paths to build artifacts rather than
+#     # `Path::join`). MinGW does not currently support these paths.
+#     if [[ "$target" = *"windows"* ]] && [[ "$target" != *"gnu"* ]]; then
+#         verb_path=$(cmd.exe //C echo \\\\?\\%cd%\\builtins-test\\target2)
+#         "${test_builtins[@]}" --target-dir "$verb_path" --features c
+#     fi
+# fi
+
+
+# echo "::group::Run symcheck"
+
+# # Ensure there are no duplicate symbols or references to `core` when
+# # `compiler-builtins` is built with various features. Symcheck invokes Cargo to
+# # build with the arguments we provide it, then validates the built artifacts.
+# SYMCHECK_TEST_TARGET="$target" cargo test -p symcheck --release
+# symcheck=(cargo run -p symcheck --release)
+# symcheck+=(-- --build-and-check --target "$target")
+
+# # Executable section checks are meaningless on no-std targets
+# [[ "$target" == *"-none"* ]] && symcheck+=(--no-os)
+
+# # We only need to check the configurations std may use
+# symcheck_cb_args=(-- --package compiler_builtins --features compiler-builtins)
+# "${symcheck[@]}" "${symcheck_cb_args[@]}"
+# "${symcheck[@]}" "${symcheck_cb_args[@]}" --release
+# "${symcheck[@]}" "${symcheck_cb_args[@]}" --features c
+# "${symcheck[@]}" "${symcheck_cb_args[@]}" --features c --release
+# "${symcheck[@]}" "${symcheck_cb_args[@]}" --no-default-features
+# "${symcheck[@]}" "${symcheck_cb_args[@]}" --no-default-features --release
+
+# echo "::endgroup"
+
+
+# echo "::group::Run intrinsics tests"
+
+# run_intrinsics_test() {
+#     build_args=(--verbose --manifest-path builtins-test-intrinsics/Cargo.toml)
+#     build_args+=("$@")
+
+#     # symcheck also checks the results of builtins-test-intrinsics
+#     "${symcheck[@]}" -- "${build_args[@]}"
+
+#     # FIXME: we get access violations on Windows, our entrypoint may need to
+#     # be tweaked.
+#     if [ "${BUILD_ONLY:-}" != "1" ] && ! [[ "$target" = *"windows"* ]]; then
+#         cargo run --target "$target" "${build_args[@]}"
+#     fi
+# }
+
+# # Verify that we haven't dropped any intrinsics/symbols
+# run_intrinsics_test
+# run_intrinsics_test --release
+# run_intrinsics_test --features c
+# run_intrinsics_test --features c --release
+
+# # Verify that there are no undefined symbols to `panic` within our
+# # implementations
+# CARGO_PROFILE_DEV_LTO=true run_intrinsics_test
+# CARGO_PROFILE_RELEASE_LTO=true run_intrinsics_test --release
+
+# echo "::endgroup"
 
 # Test libm
 
@@ -166,7 +166,7 @@ case "$target" in
     *thumb*) mflags+=(--exclude musl-math-sys) ;;
 
     # We can build musl on MinGW but running tests gets a stack overflow
-    *windows-gnu*) ;;
+    *windows-gnu*) mflags+=(--exclude musl-math-sys) ;;
 
     # Everything else gets musl enabled
     *) mflags+=(--features libm-test/build-musl) ;;
@@ -178,8 +178,10 @@ case "$target" in
     # MSVC cannot link MPFR
     *windows-msvc*) ;;
     # FIXME: MinGW should be able to build MPFR, but setup in CI is nontrivial.
-    *windows-gnu*) ;;
+    # *windows-gnu*) ;;
     # Targets that aren't cross compiled in CI work fine
+    i686-pc-windows-gnu) mflags+=(--features libm-test/build-mpfr --features gmp-mpfr-sys/force-cross,gmp-mpfr-sys/c-no-tests) ;;
+    *windows-gnu*) mflags+=(--features libm-test/build-mpfr) ;;
     aarch64*apple*) mflags+=(--features libm-test/build-mpfr) ;;
     aarch64*linux*) mflags+=(--features libm-test/build-mpfr) ;;
     i586*) mflags+=(--features libm-test/build-mpfr --features gmp-mpfr-sys/force-cross) ;;