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application-abi.md

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WASI Application ABI

In addition to the APIs defined by the various WASI modules there are also certain expectations that the WASI runtime places on an application that wishes to be portable across WASI implementations.

This document describes how a conforming WASI application is expected to behave in terms of lifecycle (startup, shutdown, etc) and any exports it is expected to include.

Current Unstable ABI

The current WASI unstable ABI specifies only two exports from a WASI application:

  • _start - the program entry point
  • memory - linear memory used by the program

The _start export must be WebAssembly function and will be used as the program entry point. This is the default name used by lld when linking WebAssembly modules. The embedder is expected to call this function once the module is instantiated.

Many of the current WASI unstable APIs require sharing of linear memory between the application and the embedder. In order to use any such APIs the WASI module is expected to export its linear memory under the name memory.

Planned Stable ABI

There is ongoing discussion about what the stable ABI might look like: