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Martin Geisler
ec71ec2040
This configures Bazel targets for the bare-metal examples. We now also
have test targets for them:
bazel test //:bare_metal_tests
will compile all the code and run a simple test in QEMU (boot the
binaries, send `"q"` to them on stdin).
The Cargo-based workflow has been kept: I expect that students will
keep using it in class, so we should keep testing it in CI.
63 lines
2.1 KiB
Python
63 lines
2.1 KiB
Python
"""Starlark Configuration Transitions for Cross-Compilation.
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In Bazel, test targets (like sh_test) are host-executed. If the global
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invocation sets --platforms=//platforms:aarch64-unknown-none, Bazel
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attempts to run the test runners themselves on the target bare-metal
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platform. Because there are no test execution toolchains for
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bare-metal targets, this results in analysis failures.
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To resolve this, we keep the global invocation targeting the host
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platform, and use these custom rules (aarch64_binary,
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thumbv7em_binary) to apply a "transition". A transition modifies the
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configuration (the --platforms flag) for the dependency edge to the
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target binary. This ensures:
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1. The binaries are always compiled for their specific bare-metal
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target platform.
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2. The parent test targets (sh_test) are built and run on the host
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platform.
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"""
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def _aarch64_transition_impl(settings, attr):
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return {"//command_line_option:platforms": ["//platforms:aarch64-unknown-none"]}
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_aarch64_transition = transition(
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implementation = _aarch64_transition_impl,
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inputs = [],
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outputs = ["//command_line_option:platforms"],
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)
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def _transition_rule_impl(ctx):
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# Retrieve the files from the transitioned target
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return [DefaultInfo(files = ctx.attr.dep[0][DefaultInfo].files)]
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aarch64_binary = rule(
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implementation = _transition_rule_impl,
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attrs = {
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"dep": attr.label(cfg = _aarch64_transition),
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"_allowlist_function_transition": attr.label(
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default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
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),
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},
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)
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def _thumbv7em_transition_impl(settings, attr):
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return {"//command_line_option:platforms": ["//platforms:thumbv7em-none-eabihf"]}
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_thumbv7em_transition = transition(
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implementation = _thumbv7em_transition_impl,
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inputs = [],
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outputs = ["//command_line_option:platforms"],
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)
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thumbv7em_binary = rule(
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implementation = _transition_rule_impl,
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attrs = {
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"dep": attr.label(cfg = _thumbv7em_transition),
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"_allowlist_function_transition": attr.label(
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default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
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),
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},
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)
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