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diff --git a/docs/WebAssembly.rst b/docs/WebAssembly.rst new file mode 100644 index 0000000000000..1df8fa3a82b05 --- /dev/null +++ b/docs/WebAssembly.rst @@ -0,0 +1,36 @@ +WebAssembly lld port +==================== + +Note: The WebAssembly port is still a work in progress and is be lacking +certain features. + +The WebAssembly version of lld takes WebAssembly binaries as inputs and produces +a WebAssembly binary as its output. For the most part this port tried to mimic +the behaviour of traditional ELF linkers and specifically the ELF lld port. +Where possible that command line flags and the semantics should be the same. + + +Object file format +------------------ + +The format the input object files that lld expects is specified as part of the +the WebAssembly tool conventions +https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md. + +This is object format that the llvm will produce when run with the +``wasm32-unknown-unknown-wasm`` target. To build llvm with WebAssembly support +currently requires enabling the experimental backed using +``-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=WebAssembly``. + + +Missing features +---------------- + +There are several key features that are not yet implement in the WebAssembly +ports: + +- COMDAT support. This means that support for C++ is still very limited. +- Function stripping. Currently there is no support for ``--gc-sections`` so + functions and data from a given object will linked as a unit. +- Section start/end symbols. The synthetic symbols that mark the start and + of data regions are not yet created in the output file. |