bazel_sysroot_llvm_arm64

This sysroot provides ARM64-specific LLVM tools for Bazel builds. It is part of a larger system of sysroots that work together to provide a complete build environment.

Purpose

The bazel_sysroot_llvm_arm64 sysroot is responsible for providing ARM64-specific LLVM tools that are required for building applications on ARM64 architectures. It works in conjunction with:

• bazel_sysroot_library - Provides common headers and system libraries
• bazel_sysroot_lib_arm64 - Provides ARM64-specific shared libraries

Required Tools

This sysroot must provide all tools required by both rules_cc and toolchain_llvm:

Core Tools (from rules_cc)

• ar (aliased from llvm-ar)
• as (aliased from llvm-as)
• ld (aliased from ld.lld)
• llvm-cov
• llvm-profdata
• cpp (aliased from clang-cpp)
• gcc (aliased from clang)
• dwp (aliased from llvm-dwp)
• gcov
• nm (aliased from llvm-nm)
• objcopy (aliased from llvm-objcopy)
• objdump (aliased from llvm-objdump)
• strip (aliased from llvm-strip)
• c++filt (aliased from llvm-c++filt)

Additional Tools (from toolchain_llvm)

• clang-cpp (from clang package)
• clang-format (from clang-tools package)
• clang-tidy (from clang-tools package)
• clangd (from clang-tools package)
• ld.lld (from lld package)
• llvm-ar (from llvm package)
• llvm-dwp (from llvm package)
• llvm-profdata (from llvm package)
• llvm-cov (from llvm package)
• llvm-nm (from llvm package)
• llvm-objcopy (from llvm package)
• llvm-objdump (from llvm package)
• llvm-strip (from llvm package)

Tool Aliasing Strategy

This sysroot implements a dual aliasing strategy to ensure compatibility with both Bazel's expectations and direct tool usage:

1. Filesystem-level aliases: During the build process, GNU tool symlinks are created in the bin/ directory:

   ln -sf clang gcc
   ln -sf clang cc
   ln -sf clang++ c++
   ln -sf clang-cpp cpp
   ln -sf llvm-ar ar
   ln -sf llvm-ar ranlib
   ln -sf llvm-as as
   ln -sf ld.lld ld
   ln -sf llvm-nm nm
   ln -sf llvm-objcopy objcopy
   ln -sf llvm-objdump objdump
   ln -sf llvm-strip strip
   ln -sf llvm-dwp dwp
   ln -sf llvm-c++filt c++filt
   ln -sf llvm-cov gcov

2. Bazel-level aliases: The BUILD.bazel file defines filegroups that map GNU tool names to their LLVM equivalents:

   filegroup(
       name = "gcc",
       srcs = [":clang"],
       visibility = ["//visibility:public"],
   )
   # ... other aliases ...

This dual approach ensures compatibility at both the filesystem level (for direct tool usage) and the Bazel level (for build system integration). While either approach alone might be sufficient, using both provides maximum compatibility and flexibility.

Directory Structure

sysroot/
└── bin/           # ARM64-specific LLVM tools
    ├── clang*     # Clang compiler tools
    ├── lld*       # LLVM linker tools
    ├── llvm-*     # Other LLVM tools
    └── llvm-dwp   # DWARF packaging tool

BUILD File Targets

The BUILD.bazel file defines the following targets:

package(default_visibility = ["//visibility:public"])

# Main sysroot filegroup
filegroup(
    name = "sysroot",
    srcs = glob(["bin/**"]),
    visibility = ["//visibility:public"],
)

# Individual tool targets
filegroup(
    name = "clang",
    srcs = glob(["bin/clang*"]),
    visibility = ["//visibility:public"],
)

filegroup(
    name = "lld",
    srcs = glob(["bin/lld*"]),
    visibility = ["//visibility:public"],
)

filegroup(
    name = "llvm-ar",
    srcs = ["bin/llvm-ar"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "llvm-as",
    srcs = ["bin/llvm-as"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "llvm-nm",
    srcs = ["bin/llvm-nm"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "llvm-objcopy",
    srcs = ["bin/llvm-objcopy"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "llvm-objdump",
    srcs = ["bin/llvm-objdump"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "llvm-readelf",
    srcs = ["bin/llvm-readelf"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "llvm-strip",
    srcs = ["bin/llvm-strip"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "llvm-dwp",
    srcs = ["bin/llvm-dwp"],
    visibility = ["//visibility:public"],
)

# Tool aliases
filegroup(
    name = "gcc",
    srcs = [":clang"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "cpp",
    srcs = [":clang"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "ar",
    srcs = [":llvm-ar"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "as",
    srcs = [":llvm-as"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "ld",
    srcs = [":lld"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "nm",
    srcs = [":llvm-nm"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "objcopy",
    srcs = [":llvm-objcopy"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "objdump",
    srcs = [":llvm-objdump"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "strip",
    srcs = [":llvm-strip"],
    visibility = ["//visibility:public"],
)

filegroup(
    name = "dwp",
    srcs = [":llvm-dwp"],
    visibility = ["//visibility:public"],
)

Usage in Bazel

This sysroot is used as part of the LLVM toolchain configuration in your MODULE.bazel:

llvm.toolchain(
    name = "llvm_arm64",
    llvm_version = "20.1.2",
    stdlib = {
        "linux-aarch64": "stdc++",
    },
)

llvm.sysroot(
    name = "llvm_arm64",
    targets = ["linux-aarch64"],
    # Main sysroot containing the LLVM tools
    label = "@bazel_sysroot_llvm_arm64//:sysroot",
    # Additional sysroots for headers and libraries
    include_prefix = "@bazel_sysroot_library//:include",
    lib_prefix = "@bazel_sysroot_lib_arm64//:lib",
    # System libraries from both common and architecture-specific sysroots
    system_libs = [
        "@bazel_sysroot_library//:system_deps",
        "@bazel_sysroot_library//:system_deps_static",
        "@bazel_sysroot_lib_arm64//:system_libs",
    ],
)

Building

To build this sysroot:

nix-build default.nix

The resulting sysroot will be available in the result/sysroot directory.

Structure

The sysroot follows a specific structure to ensure compatibility with Bazel's LLVM toolchain. For details, see SYSROOT_STRUCTURE.md.

Building

To build the sysroot:

nix build

Usage

The sysroot can be used in Bazel projects by adding it as a dependency in your MODULE.bazel file:

http_archive(
    name = "bazel_sysroot_tarball_arm64",
    urls = ["https://github.com/yourusername/bazel_sysroot_llvm_arm64/archive/refs/heads/main.tar.gz"],
    strip_prefix = "bazel_sysroot_llvm_arm64-main",
)

Notes

• All binaries are placed in the bin/ directory
• The sysroot is designed to work in conjunction with:
  • bazel_sysroot_library for common headers and system libraries
  • bazel_sysroot_lib_arm64 for ARM64-specific shared libraries
• The BUILD file provides granular access to individual tools through filegroups
• Each tool is exposed with public visibility for use in Bazel builds
• GNU tool symlinks are created to ensure compatibility with Bazel's expectations
• Excluding llvm-exegesis as it's a large benchmarking tool (75MB) not needed for compilation See https://llvm.org/docs/CommandGuide/llvm-exegesis.html for details
• The compiler-rt package is included to provide runtime libraries for LLVM sanitizers (ASan, MSan, etc.) and other runtime features. These are useful for debug builds and development, but not typically needed for production builds. See https://compiler-rt.llvm.org/ for more details.

Available Make Targets

• make help - Show available targets and their descriptions
• make update-flake - Update flake.lock with latest dependencies
• make build - Build the ARM64 LLVM toolchain using nix build
• make tarball - Create a .tar.gz archive of the ARM64 LLVM toolchain
• make nix-tarball - Create a .tar.gz archive using nix build
• make copy - Copy files from Nix store to sysroot directory
• make push - Push changes to GitHub with dated commit
• make update-all - Update flake, build, copy, and push
• make clean - Clean up build artifacts

Repository Structure

.
├── default.nix      # Nix package definition
├── flake.nix        # Nix flake configuration
├── Makefile         # Build and maintenance targets
├── sysroot/         # Sysroot files (generated)
│   ├── include/     # Header files
│   ├── lib/         # Library files
│   └── bin/         # Binary files (LLVM tools and coreutils)
└── .gitignore      # Git ignore rules

Dependencies

• Nix package manager
• rsync (for copying files)
• git (for version control)