walibc: A libc for "bare metal wasm" targets.

[!NOTE]

walibc is currently incomplete, not yet usable, and not accepting outside contributions (for the time being).

The goal of this library is to allow Rust code that targets wasm32-unknown-unknown (for example) to be able to use Rust crates that bundle C libraries. These targets are effectively bare-metal, and don't come with their own C library, even things like memcpy are unavailable (because string.h doesn't exist). Unfortunately, they're also widely used, as they don't require installing a separate SDK (such as the WASI SDK, or the Emscripten SDK). walibc exists to fill that gap.

This wouldn't be seamless (the C library bundler would have to add a build dep on walibc), but it would allow things like (for example) libsqlite3-sys to avoid the need to carry it's own implementation of libc functions.

Currently, it's essentially a header-only subset-of-libc. There aren't an abundance of good reasons for this, but the basic one is it lets us avoid linker issues if two distinct copies of walibc are used in a single build with no coordination. A better solution here is leverage cargo to solve this problem for ourselves. That said, this way we avoid colliding with functions provided by compiler_builtins...

That said, making most functions inline goes part of the way towards addressing how naïve many of our function implementations are.

Non-goals

• Supporting non-Clang compilers.
• Supporting non-wasm targets.
• Supporting non-Rust use, for now.

License

Public domain, as explained by the Unlicense. Failing that, the typical Rusty combo of Apache-2.0 or MIT is available.

Additionally:

• Portions of walibc were ported from pdclib, which is also public domain.
• The implementation of the vsnprintf-family of functions is taken from stb_sprintf (with some modifications). This is also public domain.