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+Emscripten SDK
+==============
+
+[![CircleCI](https://circleci.com/gh/emscripten-core/emsdk/tree/main.svg?style=svg)](https://circleci.com/gh/emscripten-core/emsdk/tree/main)
+
+The Emscripten toolchain is distributed as a standalone Emscripten SDK. The SDK
+provides all the required tools, such as Clang, Python and Node.js along with an
+update mechanism that enables migrating to newer Emscripten versions as they are
+released.
+
+You can also set up Emscripten from source, without the pre-built SDK, see
+"Installing from Source" below.
+
+## Downloads / How do I get the latest Emscripten build?
+
+To get started with Emscripten development, see the [Emscripten website
+documentation](https://emscripten.org/docs/getting_started/downloads.html).
+
+That explains how to use the emsdk to get the latest binary builds (without
+compiling from source). Basically, that amounts to
+
+```
+git pull
+./emsdk install latest
+./emsdk activate latest
+```
+
+## SDK Concepts
+
+The Emscripten SDK is effectively a small package manager for tools that are
+used in conjunction with Emscripten. The following glossary highlights the
+important concepts to help understanding the internals of the SDK:
+
+* **Tool**: The basic unit of software bundled in the SDK. A Tool has a name and
+  a version. For example, 'clang-3.2-32bit' is a Tool that contains the 32-bit
+  version of the Clang v3.2 compiler.
+* **SDK**: A set of tools. For example, 'sdk-1.5.6-32bit' is an SDK consisting
+  of the tools `clang-3.2-32bit`, `node-0.10.17-32bit`, `python-2.7.5.1-32bit`
+  and `emscripten-1.5.6`.
+* **Active Tool/SDK**: Emscripten SDK stores compiler configuration in a file
+  called `.emscripten` within the emsdk directory. This file points to paths
+  for Emscripten, Python, Clang and so on. If the configuration file points to a
+  Tool in a specific directory, then that tool is denoted as being
+  **active**. This mechanism allows switching between different installed
+  tools and SDKs.
+* **emsdk**: This is the name of the manager script that Emscripten SDK is
+  accessed through. Most operations are of the form `emsdk <command>`.
+
+## System Requirements
+
+Using the emsdk pre-compiled packages requires only the minimal set of
+dependencies lists below.  When building from source a wider set of tools
+include git, cmake, and a host compiler are required. See:
+https://emscripten.org/docs/building_from_source/toolchain_what_is_needed.html.
+
+### Mac OS X
+
+- macOS 11.0 or newer.
+- `java`: For running closure compiler (optional).  After installing emscripten
+  via emsdk, typing 'emcc --help' should pop up a OS X dialog "Java is not
+  installed. To open java, you need a Java SE 6 runtime. Would you like to
+  install one now?" that will automatically download a Java runtime to the
+  system.
+
+### Linux
+
+- `python`: Version 3.8 or above.
+- `java`: For running closure compiler (optional)
+
+The emsdk pre-compiled binaries are built against debian/stretch (for x86_64)
+and debian/bullseye (for arm64) sysroots and therefore depend on system
+libraries compatible with the version of `glibc` (and other libraries) present
+in those releases. If your linux distribution is very old you may not be able to
+use the pre-compiled binaries packages.  Note that `libc++` is statically linked
+so there should be no issues with older versions of `libstdc++` or `libc++`.
+
+### Windows
+
+- `java`: For running closure compiler (optional)
+
+## Uninstalling the Emscripten SDK
+
+To remove the Emscripten SDK, simply delete the emsdk directory.
+
+## SDK Maintenance
+
+The following tasks are common with the Emscripten SDK:
+
+### How do I work the emsdk utility?
+
+Run `emsdk help` or just `emsdk` to get information about all available commands.
+
+### How do I check the installation status and version of the SDK and tools?
+
+To get a list of all currently installed tools and SDK versions, and all
+available tools, run `emsdk list`.
+* A line will be printed for each tool/SDK that is available for installation.
+* The text `INSTALLED` will be shown for each tool that has already been
+  installed.
+* If a tool/SDK is currently active, a star * will be shown next to it.
+* If a tool/SDK is currently active, but the terminal your are calling emsdk
+  from does not have `PATH` and environment set up to utilize that tool, a star
+  in parentheses (\*) will be shown next to it. Run `emsdk_env.bat` (Windows) or
+  `source ./emsdk_env.sh` (Linux and OS X) to set up the environment for the
+  calling terminal.
+
+### How do I install a tool/SDK version?
+
+Run the command `emsdk install <tool/sdk name>` to download and install a new
+tool or an SDK version.
+
+### How do I remove a tool or an SDK?
+
+Run the command `emsdk uninstall <tool/sdk name>` to delete the given tool or
+SDK from the local hard drive completely.
+
+### How do I check for updates to the Emscripten SDK?
+
+`emsdk update` will fetch package information for all the new tools and
+SDK versions. After that, run `emsdk install <tool/sdk name>` to install a new
+version.
+
+### How do I install an old Emscripten compiler version?
+
+Emsdk contains a history of old compiler versions that you can use to maintain
+your migration path. Type `emsdk list --old` to get a list of archived tool and
+SDK versions, and `emsdk install <name_of_tool>` to install it.
+
+### I want to build from source!
+
+Some Emsdk Tool and SDK targets refer to packages that are precompiled, and
+no compilation is needed when installing them. Other Emsdk Tools and SDK
+targets come "from source", meaning that they will fetch the source repositories
+using git, and compile the package on demand.
+
+When you run `emsdk list`, it will group the Tools and SDKs under these two
+categories.
+
+To obtain and build latest wasm SDK from source, run
+
+```
+emsdk install sdk-main-64bit
+emsdk activate sdk-main-64bit
+```
+
+You can use this target for example to bootstrap developing patches to LLVM,
+Binaryen or Emscripten. (After initial installation, use `git remote add`
+in the cloned tree to add your own fork to push changes as patches)
+
+If you only intend to contribute to Emscripten repository, and not to LLVM
+or Binaryen, you can also use precompiled versions of them, and only git
+clone the Emscripten repository. For more details, see
+
+https://emscripten.org/docs/contributing/developers_guide.html?highlight=developer#setting-up
+
+### When working on git branches compiled from source, how do I update to a newer compiler version?
+
+Unlike tags and precompiled versions, a few of the SDK packages are based on
+"moving" git branches and compiled from source (e.g. sdk-main,
+sdk-main, emscripten-main, binaryen-main). Because of that, the
+compiled versions will eventually go out of date as new commits are introduced
+to the development branches. To update an old compiled installation of one of
+this branches, simply reissue the "emsdk install" command on that tool/SDK. This
+will `git pull` the latest changes to the branch and issue an incremental
+recompilation of the target in question. This way you can keep calling `emsdk
+install` to keep an Emscripten installation up to date with a given git branch.
+
+Note though that if the previously compiled branch is very old, sometimes CMake
+gets confused and is unable to properly rebuild a project. This has happened in
+the past e.g. when LLVM migrated to requiring a newer CMake version. In cases of
+any odd compilation errors, it is advised to try deleting the intermediate build
+directory to clear the build (e.g. "emsdk/clang/fastcomp/build_xxx/") before
+reissuing `emsdk install`.
+
+### How do I change the currently active SDK version?
+
+You can toggle between different tools and SDK versions by running `emsdk
+activate <tool/sdk name>`. Activating a tool will set up `~/.emscripten` to
+point to that particular tool. On Windows, you can pass the option `--permanent` to
+the `activate` command to register the environment permanently for the current user. Use `--system` to do this for all users.
+
+### How do I track the latest Emscripten development with the SDK?
+
+A common and supported use case of the Emscripten SDK is to enable the workflow
+where you directly interact with the github repositories. This allows you to
+obtain new features and latest fixes immediately as they are pushed to the
+github repository, without having to wait for release to be tagged. You do not
+need a github account or a fork of Emscripten to do this. To switch to using the
+latest git development branch `main`, run the following:
+
+    emsdk install git-1.9.4 # Install git. Skip if the system already has it.
+    emsdk install sdk-main-64bit # Clone+pull the latest emscripten-core/emscripten/main.
+    emsdk activate sdk-main-64bit # Set the main SDK as the currently active one.
+
+### How do I use my own Emscripten github fork with the SDK?
+
+It is also possible to use your own fork of the Emscripten repository via the
+SDK. This is achieved with standard git machinery, so if you are already
+acquainted with working on multiple remotes in a git clone, these steps should
+be familiar to you. This is useful in the case when you want to make your own
+modifications to the Emscripten toolchain, but still keep using the SDK
+environment and tools. To set up your own fork as the currently active
+Emscripten toolchain, first install the `sdk-main` SDK like shown in the
+previous section, and then run the following commands in the emsdk directory:
+
+    cd emscripten/main
+    # Add a git remote link to your own repository.
+    git remote add myremote https://github.com/mygituseraccount/emscripten.git
+    # Obtain the changes in your link.
+    git fetch myremote
+    # Switch the emscripten-main tool to use your fork.
+    git checkout -b mymain --track myremote/main
+
+In this way you can utilize the Emscripten SDK tools while using your own git
+fork. You can switch back and forth between remotes via the `git checkout`
+command as usual.
+
+### How do I use Emscripten SDK with a custom version of python, java, node.js or some other tool?
+
+The provided Emscripten SDK targets are metapackages that refer to a specific
+set of tools that have been tested to work together. For example,
+`sdk-1.35.0-64bit` is an alias to the individual packages `clang-e1.35.0-64bit`,
+`node-4.1.1-64bit`, `python-2.7.5.3-64bit` and `emscripten-1.35.0`. This means
+that if you install this version of the SDK, both python and node.js will be
+installed inside emsdk as well. If you want to use your own/system python or
+node.js instead, you can opt to install emsdk by specifying the individual set
+of packages that you want to use. For example, `emsdk install
+clang-e1.35.0-64bit emscripten-1.35.0` will only install the Emscripten
+LLVM/Clang compiler and the Emscripten frontend without supplying python and
+node.js.
+
+### My installation fails with "fatal error: ld terminated with signal 9 [Killed]"?
+
+This may happen if the system runs out of memory. If you are attempting to build
+one of the packages from source and are running in a virtual OS or may have
+relatively little RAM and disk space available, then the build might fail. Try
+feeding your computer more memory. Another thing to try is to force emsdk
+install to build in a singlethreaded mode, which will require less RAM
+simultaneously. To do this, pass the `-j1` flag to the `emsdk install` command.
+
+### How do I run Emscripten on 32-bit systems or non-x86-64 systems?
+
+Emscripten SDK releases are no longer packaged or maintained for 32-bit systems.
+If you want to run Emscripten on a 32-bit system, you can try manually building
+the compiler. Follow the steps in the above section "Building an Emscripten tag
+or branch from source" to get started.