[libc][workflow] address permission concern and add more comments

[SchrodingerZhu]

This patch limits the permission of pre-commit libc pipelines. It also adds detailed comments to help future modifications.

[llvmbot]

@llvm/pr-subscribers-github-workflow

@llvm/pr-subscribers-libc

Author: Schrodinger ZHU Yifan (SchrodingerZhu)

Changes

This patch limits the permission of pre-commit libc pipelines. It also adds detailed comments for help future modifications.

---

Full diff: https://github.com/llvm/llvm-project/pull/119320.diff

3 Files Affected:

• (modified) .github/workflows/libc-fullbuild-tests.yml (+16-3)
• (modified) .github/workflows/libc-overlay-tests.yml (+16-2)
• (modified) libc/src/__support/FPUtil/aarch64/FEnvImpl.h (+1-1)

diff --git a/.github/workflows/libc-fullbuild-tests.yml b/.github/workflows/libc-fullbuild-tests.yml
index fb73aa392f3433..b07e94244c2e8c 100644
--- a/.github/workflows/libc-fullbuild-tests.yml
+++ b/.github/workflows/libc-fullbuild-tests.yml
@@ -1,6 +1,7 @@
 # This workflow is for pre-commit testing of the LLVM-libc project.
 name: LLVM-libc Pre-commit Fullbuild Tests
-
+permissions:
+  contents: read
 on:
   pull_request:
     branches: [ "main" ]
@@ -22,7 +23,13 @@ jobs:
           #   cpp_compiler: g++
     steps:
     - uses: actions/checkout@v4
-
+    
+    # Libc's build is relatively small comparing with other components of LLVM.
+    # A fresh fullbuild takes about 190MiB of uncompressed disk space, which can
+    # be compressed into ~40MiB. Limiting the cache size to 1G should be enough.
+    # Prefer sccache as it is more modern.
+    # Do not use direct GHAC access even though it is supported by sccache. GHAC rejects
+    # frequent small object writes.
     - name: Setup ccache
       uses: hendrikmuhs/ccache-action@v1.2
       with:
@@ -30,6 +37,10 @@ jobs:
         key: libc_fullbuild_${{ matrix.c_compiler }}
         variant: sccache
     
+    # Notice:
+    # - MPFR is required by some of the mathlib tests.
+    # - Debian has a multilib setup, so we need to symlink the asm directory.
+    #   For more information, see https://wiki.debian.org/Multiarch/LibraryPathOverview
     - name: Prepare dependencies (Ubuntu)
       run: |
         sudo apt-get update
@@ -42,7 +53,9 @@ jobs:
       run: |
         echo "build-output-dir=${{ github.workspace }}/build" >> "$GITHUB_OUTPUT"
         echo "build-install-dir=${{ github.workspace }}/install" >> "$GITHUB_OUTPUT"
-
+    
+    # Configure libc fullbuild with scudo.
+    # Use MinSizeRel to reduce the size of the build.
     - name: Configure CMake
       run: >
         cmake -B ${{ steps.strings.outputs.build-output-dir }}
diff --git a/.github/workflows/libc-overlay-tests.yml b/.github/workflows/libc-overlay-tests.yml
index d0cdfdef99fe96..8b59d76aed4a88 100644
--- a/.github/workflows/libc-overlay-tests.yml
+++ b/.github/workflows/libc-overlay-tests.yml
@@ -1,6 +1,7 @@
 # This workflow is for pre-commit testing of the LLVM-libc project.
 name: LLVM-libc Pre-commit Overlay Tests
-
+permissions:
+  contents: read
 on:
   pull_request:
     branches: [ "main" ]
@@ -32,7 +33,14 @@ jobs:
     
     steps:
     - uses: actions/checkout@v4
-
+    
+    # Libc's build is relatively small comparing with other components of LLVM.
+    # A fresh linux overlay takes about 180MiB of uncompressed disk space, which can
+    # be compressed into ~40MiB. MacOS and Windows overlay builds are less than 10MiB
+    # after compression. Limiting the cache size to 1G should be enough.
+    # Prefer sccache as it is modern and it has a guarantee to work with MSVC.
+    # Do not use direct GHAC access even though it is supported by sccache. GHAC rejects
+    # frequent small object writes.
     - name: Setup ccache
       uses: hendrikmuhs/ccache-action@v1
       with:
@@ -40,12 +48,15 @@ jobs:
         key: libc_overlay_build_${{ matrix.os }}_${{ matrix.compiler.c_compiler }}
         variant: sccache
     
+    # MPFR is required by some of the mathlib tests.
     - name: Prepare dependencies (Ubuntu)
       if: runner.os == 'Linux'
       run: |
         sudo apt-get update
         sudo apt-get install -y libmpfr-dev libgmp-dev libmpc-dev ninja-build
     
+    # Chocolatey is shipped with Windows runners. Windows Server 2025 recommends WinGet.
+    # Consider migrating to WinGet when Windows Server 2025 is available.
     - name: Prepare dependencies (Windows)
       if: runner.os == 'Windows'
       run: |
@@ -62,6 +73,9 @@ jobs:
       run: |
         echo "build-output-dir=${{ github.workspace }}/build" >> "$GITHUB_OUTPUT"
 
+    # Use MinSizeRel to reduce the size of the build.
+    # Notice that CMP0141=NEW and MSVC_DEBUG_INFORMATION_FORMAT=Embedded are required
+    # by the sccache tool.
     - name: Configure CMake
       run: >
         cmake -B ${{ steps.strings.outputs.build-output-dir }}
diff --git a/libc/src/__support/FPUtil/aarch64/FEnvImpl.h b/libc/src/__support/FPUtil/aarch64/FEnvImpl.h
index 18b0631324f8fb..e41e7a2f5ba77e 100644
--- a/libc/src/__support/FPUtil/aarch64/FEnvImpl.h
+++ b/libc/src/__support/FPUtil/aarch64/FEnvImpl.h
@@ -59,7 +59,7 @@ struct FEnv {
            ((excepts & FE_UNDERFLOW) ? UNDERFLOW_F : 0) |
            ((excepts & FE_INEXACT) ? INEXACT_F : 0);
   }
-
+# 1 "/usr/include/x86_64-linux-gnu/bits/fcntl-linux.h" 1 3 4
   LIBC_INLINE static int exceptionStatusToMacro(uint32_t status) {
     return ((status & INVALID_F) ? FE_INVALID : 0) |
            ((status & DIVBYZERO_F) ? FE_DIVBYZERO : 0) |

[tstellar]

LGTM. Thank you.