Configuring Emscripten Settings when Manually Building from Source

Emscripten can be configured via a compiler configuration file (.emscripten). These settings include paths to the tools (LLVM, Clang, Binaryen, etc.) and the compiler’s temporary directory for intermediate build files.

This confuration file is optional. By default, emscripten will search for the tools it needs in the PATH.

This article explains how to create and update the file when you are building Emscripten manually from source.

Creating the compiler configuration file

A settings file may be used when running emcc (or any of the other Emscripten tools). You can run emcc with --generate-config in order to generate one in the default location.

  1. Navigate to the directory where you cloned the Emscripten repository.

  2. Enter the command:

./emcc --generate-config

You should get a An Emscripten settings file has been generated at: message, along with the contents of the config file.

When generating this file Emscripten will make its “best guess” at the correct locations for tools based on the current PATH.

In most cases it will be necessary to edit the generated file and modify least the LLVM_ROOT and BINARYEN_ROOT settings to point to the correct locations for your local LLVM and Binaryen installations.

Locating the compiler configuration file (.emscripten)

The settings file (.emscripten) is created by default within the emscripten directory (alongsize emcc itself). In cases where the emscripten directory is read-only the user’s home directory will be used:

  • On Linux and macOS this file is named ~/.emscripten, where ~ is the user’s home directory.

    Note

    Files with the “.” prefix are hidden by default. You may need to change your view settings to find the file.

  • On Windows the file can be found at a path like: C:/Users/yourusername_000/.emscripten.

Compiler configuration file-format

Note

While the syntax is identical, the appearance of the default .emscripten file created by emcc is quite different than that created by emsdk. This is because emsdk manages multiple target environments, and where possible hard codes the locations of those tools when a new environment is activated. The default file, by contrast, is managed by the user — and is designed to make that task as easy as possible.

The file simply assigns values to a number of variables representing the main tools used by Emscripten. For example, if your binaryen installation is in C:\tools\binaryen\, then the file might contain the line:

BINARYEN_ROOT = 'C:\\tools\\binaryen\\'

You can find out the other variable names from the default .emscripten file or the example here.

Editing the compiler configuration file

The compiler configuration file can be edited with the text editor of your choice. If you’re building manually from source, you are most likely to have to update the variable LLVM_ROOT

  1. Edit the variable LLVM_ROOT to point to the directory where you built the LLVM binaries, such as:

    LLVM_ROOT = '/home/ubuntu/a-path/llvm/build/bin'
    

    Note

    Use forward slashes!

After setting those paths, run emcc again. It should again perform the sanity checks to test the specified paths. There are further validation tests available at Verifying the Emscripten Development Environment.