Troubleshooting

These are some common issues you may run into while using SwiftWasm.

If you are having trouble that is not listed here, try searching for it in the SwiftWasm issue tracker. If you are still having trouble, please file an issue or contact us at the community Discord server.

RuntimeError: memory access out of bounds

If you encounter this error, there are 3 possible causes:

1. You are trying to access invalid memory in your code

In this case, you need to make sure which memory operations are invalid in your code by UnsafePointer or C code.

2. You missed program initialization defined in WASI Application ABI.

If your application is used as a library, you need to follow WASI reactor ABI.

Please make sure that you followed it by reviewing the Exporting function guide

3. Stack overflow is occurring.

If you are using --stack-first linker option (carton uses it by default), you can face RuntimeError: memory access out of bounds error due to stack overflow.

You have two options to solve this issue:

  1. Avoid recursive calls if possible.

  2. Extend the stack size by linker option -z stack-size=<size>. The default stack size is 64KB

    swift build --triple wasm32-unknown-wasi -Xlinker -z -Xlinker stack-size=131072

  3. Identify which function consumes a lof of stack space by some tools like wasm-stack-consumer

See also: LLVM Bugzilla – wasm32: Allow placing the stack before global data

fatal error: 'stdlib.h' file not found

If you encounter this error, please make sure that:

  • You are using SwiftWasm toolchain (if you installed it as a toolchain, not as a Swift SDK)
    • Check which swift and make sure it points to the SwiftWasm toolchain.
  • You are using the correct target triple:
    • --triple wasm32-unknown-wasi --static-swift-stdlib if you installed as a toolchain
    • --swift-sdk wasm32-unknown-wasi if you installed as a Swift SDK

error: missing external dependency '.../usr/lib/swift/wasi/static-executable-args.lnk'

You may encounter this error while building with Swift SDK for WebAssembly and swiftc driver command. Unfortunately, Swift SDK does not support building with swiftc command yet, so you need to use swift build Swift Package Manager command instead.

e.g. swift build --swift-sdk <SDK name>

See also: Compile a SwiftPM package to WebAssembly