secp256k1-wasm

EMCC+LLVM WebAssembly bindings for libsecp256k1

This project provides Emscripten WASM bindings for libsecp256k1 and provides basic scaffolding to build the native libsecp256k1 C code to WASM using EMCC.

Building secp256k1-wasm

Repositories you will need to clone:

$ git clone https://github.com/aspectron/secp256k1-wasm
$ git clone https://github.com/WebAssembly/binaryen
$ git clone https://github.com/llvm/llvm-project
$ git clone https://github.com/emscripten-core/emscripten

Building Binaryen:

$ cd binaryen
$ cmake .
$ cmake --build . --config Release -j NNN
NNN = number of CPU cores/threads

Override emscripten src files:

$ cp emscripten_override/src/* to emscripten/src/

The following process builds LLVM inside the ./emscripten/build folder:

$ cd emscripten
$ mkdir build
$ cd build/
$ cmake ../../llvm-project/llvm -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS='lld;clang' -DLLVM_TARGETS_TO_BUILD="host;WebAssembly" -DLLVM_INCLUDE_EXAMPLES=OFF -DLLVM_INCLUDE_TESTS=OFF
$ cmake --build . --config Release -j NNN
NNN = number of CPU cores/threads
$ cd ..     

We are now back in the Emscripten folder. Generate the default .emscripten file:

$ ./emcc  -v

Edit the .emscripten file to contain correct paths to LLVM and Binaryen:

• point LLVM_ROOT to <path to emscripten>/build/bin or <path to emscripten>/build/Release/bin if LLVM was built using Visual C++
• point BINARYEN_ROOT to <path to binaryen>

Re-run ./emcc -v to check that everything is ok. You should now see the version of EMCC, clang and InstalledDir information.

Build secp256k1-wasm:

You can run ./build or build.bat to build the WASM binaries or execute the following:

$ emcc -I ./depend/secp256k1 -I ./depend/secp256k1/src secp256k1-bindings.cpp -o http/secp256k1.html -s EXTRA_EXPORTED_RUNTIME_METHODS=["cwrap"] -std=c++11 --bind -s ALLOW_MEMORY_GROWTH=1 -s IMPORTED_MEMORY

To test the build, you will require an installed version of NodeJs. From within the secp256k1-wasm folder please run the following:

using python SimpleHTTPServer:

$ python -m SimpleHTTPServer 8000

using nodejs:

$ npm install
$ node test/node-server

You should now be able to access the emscripten environment with secp256k1 loaded at http://localhost:3000