| commit e48fd8490d497fdfa6d5a7f8a3af63cc8c6db538 |
| Author: Jan Schär <jan@monogon.tech> |
| Date: Thu Jul 3 16:03:25 2025 +0000 |
| |
| Use musl toolchain and add loader_wrapper |
| |
| This patches rules_rust to use the Rust toolchain built for musl instead |
| of glibc, and adds a wrapper to locate the dynamic loader. What we |
| achieve with this is that we no longer need a specific loader installed |
| at an absolute path, which makes the build less dependent on the host |
| OS. |
| |
| The tools are linked dynamically and need libc.so and libgcc_s.so.1. At |
| least rustc cannot be linked statically, because proc macros are loaded |
| with dlopen. When building proc macros, we need to add library paths |
| containing the two .so files such that lld can find them. |
| |
| Usually, musl would be installed at /lib/ld-musl-x86_64.so.1, but we |
| can't do that. Instead, the binaries are renamed to {name}_real and a |
| wrapper script is placed there instead. The wrapper runs musl as a |
| dynamic loader, passing it the path to the real binary. |
| |
| diff --git a/rust/platform/triple.bzl b/rust/platform/triple.bzl |
| index 87cd6242..766bc08e 100644 |
| --- a/rust/platform/triple.bzl |
| +++ b/rust/platform/triple.bzl |
| @@ -138,7 +138,7 @@ def get_host_triple(repository_ctx, abi = {}): |
| prefix = "{}-unknown-linux".format(arch) |
| return triple("{}-{}".format( |
| prefix, |
| - abi.get(prefix, "gnu"), |
| + abi.get(prefix, "musl"), |
| )) |
| |
| if "mac" in repository_ctx.os.name: |
| diff --git a/rust/private/loader_wrapper.sh b/rust/private/loader_wrapper.sh |
| new file mode 100755 |
| index 00000000..29805d8d |
| --- /dev/null |
| +++ b/rust/private/loader_wrapper.sh |
| @@ -0,0 +1,51 @@ |
| +#!/bin/sh |
| + |
| +# Running rustc and other tools directly doesn't work, because that would |
| +# require musl to be installed at /lib/ld-musl-x86_64.so.1, but we can't install |
| +# things at absolute paths. Instead, this script calls musl as a dynamic loader, |
| +# giving it the path to the real binary which has been renamed to {name}_real. |
| + |
| +set -eu |
| + |
| +dirname() { |
| + # Usage: dirname "path" |
| + |
| + # If '$1' is empty set 'dir' to '.', else '$1'. |
| + dir=${1:-.} |
| + |
| + # Strip all trailing forward-slashes '/' from |
| + # the end of the string. |
| + # |
| + # "${dir##*[!/]}": Remove all non-forward-slashes |
| + # from the start of the string, leaving us with only |
| + # the trailing slashes. |
| + # "${dir%%"${}"}": Remove the result of the above |
| + # substitution (a string of forward slashes) from the |
| + # end of the original string. |
| + dir=${dir%%"${dir##*[!/]}"} |
| + |
| + # If the variable *does not* contain any forward slashes |
| + # set its value to '.'. |
| + [ "${dir##*/*}" ] && dir=. |
| + |
| + # Remove everything *after* the last forward-slash '/'. |
| + dir=${dir%/*} |
| + |
| + # Again, strip all trailing forward-slashes '/' from |
| + # the end of the string (see above). |
| + dir=${dir%%"${dir##*[!/]}"} |
| + |
| + # Print the resulting string and if it is empty, |
| + # print '/'. |
| + printf '%s\n' "${dir:-/}" |
| +} |
| + |
| +selfDir="$(dirname "$0")" |
| +rootPath="$(dirname "$selfDir")" |
| + |
| +exec "${rootPath}/sysroot/usr/lib/libc.so" \ |
| + "--library-path=${rootPath}/sysroot/usr/lib" \ |
| + "--argv0" "$0" \ |
| + "--" \ |
| + "${0}_real" \ |
| + "$@" |
| diff --git a/rust/private/repository_utils.bzl b/rust/private/repository_utils.bzl |
| index 27c08e78..0761c34c 100644 |
| --- a/rust/private/repository_utils.bzl |
| +++ b/rust/private/repository_utils.bzl |
| @@ -41,12 +41,16 @@ filegroup( |
| name = "rustc_lib", |
| srcs = glob( |
| [ |
| + "bin/*_real", |
| "bin/*{dylib_ext}", |
| "lib/*{dylib_ext}*", |
| "lib/rustlib/{target_triple}/codegen-backends/*{dylib_ext}", |
| "lib/rustlib/{target_triple}/bin/rust-lld{binary_ext}", |
| "lib/rustlib/{target_triple}/lib/*{dylib_ext}*", |
| "lib/rustlib/{target_triple}/lib/*.rmeta", |
| + "sysroot/usr/lib/libc.so", |
| + "sysroot/usr/lib/libgcc_s.so*", |
| + "sysroot/usr/lib/libunwind.so*", |
| ], |
| allow_empty = True, |
| ), |
| diff --git a/rust/private/rustc.bzl b/rust/private/rustc.bzl |
| index d78c2890..fbc00591 100644 |
| --- a/rust/private/rustc.bzl |
| +++ b/rust/private/rustc.bzl |
| @@ -1012,6 +1012,12 @@ def construct_arguments( |
| if linker_script: |
| rustc_flags.add(linker_script, format = "--codegen=link-arg=-T%s") |
| |
| + if is_exec_configuration(ctx): |
| + # This is needed when building proc macros, for lld to find libgcc_s.so |
| + # and libc.so. This must be before the Rust standard library paths so |
| + # lld uses libc.so instead of the libc.a shipped by Rust. |
| + rustc_flags.add("-L", "native={}/sysroot/usr/lib".format(tool_path.rsplit("/", 2)[0])) |
| + |
| # Tell Rustc where to find the standard library (or libcore) |
| rustc_flags.add_all(toolchain.rust_std_paths, before_each = "-L", format_each = "%s") |
| rustc_flags.add_all(rust_flags, map_each = map_flag) |
| diff --git a/rust/repositories.bzl b/rust/repositories.bzl |
| index a5df3842..323a26ae 100644 |
| --- a/rust/repositories.bzl |
| +++ b/rust/repositories.bzl |
| @@ -42,13 +42,13 @@ load_arbitrary_tool = _load_arbitrary_tool |
| DEFAULT_TOOLCHAIN_TRIPLES = { |
| "aarch64-apple-darwin": "rust_macos_aarch64", |
| "aarch64-pc-windows-msvc": "rust_windows_aarch64", |
| - "aarch64-unknown-linux-gnu": "rust_linux_aarch64", |
| + "aarch64-unknown-linux-musl": "rust_linux_aarch64", |
| "powerpc64le-unknown-linux-gnu": "rust_linux_powerpc64le", |
| "s390x-unknown-linux-gnu": "rust_linux_s390x", |
| "x86_64-apple-darwin": "rust_macos_x86_64", |
| "x86_64-pc-windows-msvc": "rust_windows_x86_64", |
| "x86_64-unknown-freebsd": "rust_freebsd_x86_64", |
| - "x86_64-unknown-linux-gnu": "rust_linux_x86_64", |
| + "x86_64-unknown-linux-musl": "rust_linux_x86_64", |
| } |
| |
| _COMPACT_WINDOWS_NAMES = True |
| @@ -349,6 +349,33 @@ def rust_repositories(**kwargs): |
| |
| rust_register_toolchains(**kwargs) |
| |
| +def load_sysroot(ctx, target_triple): |
| + # Download the sysroot. We only need libc.so and libunwind.so from this; |
| + # they are runtime dependencies of rustc, cargo, etc. |
| + ARTIFACTS_VERSION = "20250603" |
| + if target_triple.arch == "x86_64": |
| + ctx.download_and_extract( |
| + ["https://monogon-llvm-toolchain.storage.googleapis.com/%s/sysroot-x86_64-unknown-linux-musl.tar.zst" % ARTIFACTS_VERSION], |
| + sha256 = "ba0fce4438de6d4dbc1678d2e672f377d30327d24e10b0de09f090032d34c1ba", |
| + output = "sysroot", |
| + ) |
| + elif target_triple.arch == "aarch64": |
| + ctx.download_and_extract( |
| + ["https://monogon-llvm-toolchain.storage.googleapis.com/%s/sysroot-aarch64-unknown-linux-musl.tar.zst" % ARTIFACTS_VERSION], |
| + sha256 = "0cee4d5c1d24a9e9e2d1d12fd5e05ea1afcf69ea0b5d43979290988143ce1a0f", |
| + output = "sysroot", |
| + ) |
| + else: |
| + fail("missing sysroot for architecture {}".format(target_triple.arch)) |
| + # Rust uses either libgcc_s.so or libunwind.so for unwinding. Both have the |
| + # same interface for unwinding, so we can make libgcc_s.so a symlink to |
| + # libunwind.so and it will work. This could potentially break in unknown |
| + # ways, but it didn't break so far. Unwinding was tested by inserting a |
| + # panic in a proc macro, which worked as expected. This avoids us needing to |
| + # either build libgcc_s.so or build Rust configured to use libunwind.so. |
| + ctx.symlink("sysroot/usr/lib/libunwind.so.1.0", "sysroot/usr/lib/libgcc_s.so.1") |
| + ctx.symlink("sysroot/usr/lib/libunwind.so.1.0", "sysroot/usr/lib/libgcc_s.so") |
| + |
| _RUST_TOOLCHAIN_REPOSITORY_ATTRS = { |
| "allocator_library": attr.string( |
| doc = "Target that provides allocator functions when rust_library targets are embedded in a cc_binary.", |
| @@ -539,6 +566,13 @@ def _rust_toolchain_tools_repository_impl(ctx): |
| repro[key] = getattr(ctx.attr, key) |
| repro["sha256s"] = sha256s |
| |
| + load_sysroot(ctx = ctx, target_triple = exec_triple) |
| + loader_wrapper = ctx.read(Label("//rust/private:loader_wrapper.sh")) |
| + ctx.rename("bin/cargo", "bin/cargo_real") |
| + ctx.file("bin/cargo", loader_wrapper) |
| + ctx.rename("bin/rustc", "bin/rustc_real") |
| + ctx.file("bin/rustc", loader_wrapper) |
| + |
| return repro |
| |
| rust_toolchain_tools_repository = repository_rule( |
| @@ -928,6 +962,11 @@ def _rustfmt_toolchain_tools_repository_impl(repository_ctx): |
| repro[key] = getattr(repository_ctx.attr, key) |
| repro["sha256s"] = sha256s |
| |
| + load_sysroot(ctx = repository_ctx, target_triple = exec_triple) |
| + loader_wrapper = repository_ctx.read(Label("//rust/private:loader_wrapper.sh")) |
| + repository_ctx.rename("bin/rustfmt", "bin/rustfmt_real") |
| + repository_ctx.file("bin/rustfmt", loader_wrapper) |
| + |
| return repro |
| |
| rustfmt_toolchain_tools_repository = repository_rule( |