WebAssembly Build for libsepol

This document describes how to build libsepol for WebAssembly using Emscripten.

Prerequisites

1. Emscripten SDK: Ensure you have Emscripten installed and available in your PATH.
   • Follow the instructions at emscripten.org.
2. Build Dependencies: You need make, flex, and bison installed on your system.
   • On Debian/Ubuntu: sudo apt-get install make flex bison

Compilation Steps

To build libsepol for WebAssembly, use the provided Makefile.wasm:

cd libsepol
# Build for Node.js and static library
make -f Makefile.wasm

# Build specifically for the browser example
make -f Makefile.wasm browser

Build Artifacts

• libsepol/src/libsepol.a: The static library for linking into other WASM projects.
• libsepol/src/libsepol_browser.js / .wasm: Unified module for browser use.
• libsepol/utils/*.js and libsepol/utils/*.wasm: The utility programs as JavaScript/WebAssembly modules (configured for Node.js).

Usage

Browser Example

A runnable browser example is provided in libsepol/wasm_example/.

1. Build the browser target: make -f Makefile.wasm browser
2. Serve the root directory with a web server. For example:

   python3 -m http.server 8000

3. Navigate to http://localhost:8000/libsepol/wasm_example/ in your browser.

The example demonstrates how to initialize the library and call sepol_check_context using Emscripten's cwrap.

Using Utilities with Node.js

You can run the built utilities using Node.js. Note that due to how WASM files are loaded, you might need to be in the same directory or use a tool that handles the resolution.

cd libsepol/utils
node chkcon.js

Linking into a WASM Project

To use libsepol in your own C/C++ project compiled with Emscripten, include the headers and link against the static library:

emcc my_app.c -Ipath/to/libsepol/include path/to/libsepol/src/libsepol.a -o my_app.js

Customizing the Build

You can customize the Emscripten flags by editing libsepol/Makefile.wasm or by passing them on the command line:

make -f Makefile.wasm WASM_CFLAGS="-O3" WASM_LDFLAGS="-s EXPORTED_FUNCTIONS=['_sepol_policydb_read']"

Compatibility Notes

• reallocarray: Provided via libsepol/src/wasm_compat.c to avoid conflicts between Emscripten's stdlib.h declaration and the lack of implementation in some environments.
• SINGLE_FILE=1: Can be added to WASM_LDFLAGS if you wish to embed the WASM binary directly into the JS file.