Emscripten 安装

通过 Homebrew 安装

可以通过官方的 Download and install 页面描述的步骤来进行，但也有更加便捷的方式，比如通过 Homebrew，只需执行如下命令即可：

$ brew install emscripten

.emscripten 文件的配置

完成成功后， 会有个配置的提示：

==> Caveats
Manually set LLVM_ROOT to
  /usr/local/opt/emscripten/libexec/llvm/bin
and comment out BINARYEN_ROOT
in ~/.emscripten after running `emcc` for the first time.

即首次运行 emcc 后，会生成一个 ~/.emscripten 配置文件，将其中的 LLVM_ROOT 设置成上面提示的路径，同时注释掉 BINARYEN_ROOT。

运行 emcc 检查安装

运行 emcc 检查是否安装成功：

$ emcc -v
==============================================================================
Welcome to Emscripten!

This is the first time any of the Emscripten tools has been run.

A settings file has been copied to ~/.emscripten, at absolute path: /Users/wayou/.emscripten

It contains our best guesses for the important paths, which are:

  LLVM_ROOT       = /usr/bin
  NODE_JS         = /Users/wayou/.nvm/versions/node/v12.1.0/bin/node
  EMSCRIPTEN_ROOT = /usr/local/Cellar/emscripten/1.39.8/libexec

Please edit the file if any of those are incorrect.

This command will now exit. When you are done editing those paths, re-run it.
==============================================================================

然后按照上面提示配置 ~/.emscripten，再次运行 emcc 时，如果是 1.38.44 之后的版本，会发现报错：

$ emcc -v
shared:ERROR: BINARYEN_ROOT is not defined in /Users/wayou/.emscripten

BINARYEN_ROOT 的设置

因为前面步骤注释掉了 BINARYEN_ROOT，所以这里提示该字段没有设置。查询后发现这里有对这个问题的讨论，具体原因来自 1.38.44 中的改动：

v1.38.44: 09/11/2019

  • Remove Binaryen from the ports system. This means that emscripten will no longer automatically build Binaryen from source. Instead, either use the emsdk (binaries are provided automatically, just like for LLVM), or build it yourself and point BINARYEN_ROOT in .emscripten to it. See #9409 -- 引用自 emscripten 的发版日志

解决办法是安装 binaryen 并且设置 BINARYEN_ROOT 到 /usr/local/opt/binaryen 这个路径。

$ brew install binaryen

编辑 ~/.emscripten 设置 BINARYEN_ROOT：

BINARYEN_ROOT = '/usr/local/opt/binaryen'

再次运行 emcc 检查是否一切正常：

$ emcc -v
cache:INFO: generating system asset: is_vanilla.txt... (this will be cached in "/Users/wayou/.emscripten_cache/is_vanilla.txt" for subsequent builds)
cache:INFO:  - ok
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 1.39.8
clang version 6.0.1  (emscripten 1.39.8 : 1.39.8)
Target: x86_64-apple-darwin19.3.0
Thread model: posix
InstalledDir: /usr/local/opt/emscripten/libexec/llvm/bin
shared:INFO: (Emscripten: Running sanity checks)

至此，通过 Homebrew 方式成功安装 emscripten。

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