WASI Application ABI
====================

In addition to the APIs defined by the various WASI [modules](modules.md) 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:

- https://github.com/WebAssembly/WASI/issues/13
- https://github.com/WebAssembly/WASI/issues/19
- https://github.com/WebAssembly/WASI/issues/24