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Implement support for macOS Apple Silicon => x86_64 cross compilation #2958

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Merged
fhanau merged 1 commit into from
Oct 21, 2024
Merged

Implement support for macOS Apple Silicon => x86_64 cross compilation #2958

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13 changes: 13 additions & 0 deletions .bazelrc
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Original file line number Diff line number Diff line change
Expand Up @@ -221,6 +221,19 @@ build:macos --copt='-femit-dwarf-unwind=no-compact-unwind'
# TODO(soon): File a bazel issue for the flag so we can drop this.
build:macos --experimental_objc_fastbuild_options=""

# Cross-Compilation
# Only cross-compiling on macOS from Apple Silicon to x86_64 is supported – using apple_support
# makes this much easier than on other platforms. We could define a configuration for cross-
# compiling from Intel Mac too, but it lacks a means to run Apple Silicon binaries. We would have to
# change V8 mksnapshot to build in the host configuration again (effectively compiling much of V8
# twice) and couldn't run tests, so it would provide little value.
#
# Define the target platform
build:macos-cross-x86_64 --cpu=darwin_x86_64 --host_cpu=darwin_arm64 --platforms //:macOS_x86
# Some cross-compiled tests are slower when run over Rosetta, increase the medium test size timeout.
# Test performance is still very much satisfactory considering that emulation is being used here.
build:macos-cross-x86_64 --test_timeout=1,30,60,240

# On Linux, always link libc++ statically to avoid compatibility issues with different OS versions.
# macOS links with dynamic libc++ by default, which has good backwards compatibility.
# Drop default link flags, which include libstdc++ for Linux
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9 changes: 9 additions & 0 deletions BUILD.bazel
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Expand Up @@ -46,6 +46,15 @@ platform(
],
)

# Used for cross-compilation
platform(
name = "macOS_x86",
constraint_values = [
"@platforms//os:macos",
"@platforms//cpu:x86_64",
],
)

# bazel enables the --ffunction-sections, --gc-sections flags used to remove dead code by default
# on Linux opt builds. Enable the equivalent macOS flag -Wl,-dead_strip here to work around bazel
# idiosyncrasies.
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7 changes: 5 additions & 2 deletions WORKSPACE
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Expand Up @@ -178,8 +178,11 @@ rules_rust_dependencies()

rust_register_toolchains(
edition = "2021",
# Rust registers wasm targets by default which we don't need, workerd is only built for its native platform.
extra_target_triples = [],
# Add support macOS cross-compilation, the overhead for this is limited with only a few more
# targets being generated for the extra triple as part of the toolchain. Setting this explicitly
# also avoids registering support for the wasm32-unknown-unknown and wasm32-wasi targets, which
# are otherwise added by default.
extra_target_triples = ["x86_64-apple-darwin"],
versions = ["1.81.0"], # LLVM 18
)

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