459f7c14f6
* Update bazel/README.md * Add deps instantiation to readme * Add bazelrc explanations to readme * Note the preferred way of using bazel emsdk
62 lines
1.8 KiB
Markdown
62 lines
1.8 KiB
Markdown
# Bazel Emscripten toolchain
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## Setup Instructions
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In `WORKSPACE` file, put:
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```
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load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
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http_archive(
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name = "emsdk",
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strip_prefix = "emsdk-c1589b55641787d55d53e883852035beea9aec3f/bazel",
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url = "https://github.com/emscripten-core/emsdk/archive/c1589b55641787d55d53e883852035beea9aec3f.tar.gz",
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sha256 = "7a58a9996b113d3e0675df30b5f17e28aa47de2e684a844f05394fe2f6f12e8e",
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)
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load("@emsdk//:deps.bzl", emsdk_deps = "deps")
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emsdk_deps()
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load("@emsdk//:emscripten_deps.bzl", emsdk_emscripten_deps = "emscripten_deps")
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emsdk_emscripten_deps()
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```
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## Building
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### Using --config=wasm
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Put the following lines into your `.bazelrc`:
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```
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build:wasm --crosstool_top=//emscripten_toolchain:everything
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build:wasm --cpu=wasm
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build:wasm --host_crosstool_top=@bazel_tools//tools/cpp:toolchain
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```
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Simply pass `--config=wasm` when building a normal `cc_binary`. The result of
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this build will be a tar archive containing any files produced by emscripten.
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### Using wasm_cc_binary
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First, write a new rule wrapping your `cc_binary`.
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```
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load("@rules_cc//cc:defs.bzl", "cc_binary")
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load("@emsdk//emscripten_toolchain:wasm_rules.bzl", "wasm_cc_binary")
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cc_binary(
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name = "hello-world",
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srcs = ["hello-world.cc"],
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)
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wasm_cc_binary(
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name = "hello-world-wasm",
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cc_target = ":hello-world",
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)
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```
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Now you can run `bazel build :hello-world-wasm`. The result of this build will
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be the individual files produced by emscripten. Note that some of these files
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may be empty. This is because bazel has no concept of optional outputs for
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rules.
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`wasm_cc_binary` uses transition to use emscripten toolchain on `cc_target`
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and all of its dependencies, and does not require amending `.bazelrc`. This
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is the preferred way, since it also unpacks the resulting tarball.
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