Incorrect size returned by __wasi_environ_sizes_get

[shritesh]

The documentation for __wasi_environ_get says "The sizes of the buffers should match that returned by __wasi_environ_sizes_get" but the WASI implementations that I tested (wasmtime and wasmer) expect a buffer with space for additional null pointer at the end. The sysroot too implements it that way.

This is in contrast with __wasi_args_get and __wasi_args_sizes_get that say the same thing but do as documented.

I'm not sure if this is a bug or the expected behavior. If it is, it should be documented as such.

[sbc100]

The C arrays exposed to user code for environ and argv are are both defined to be NULL terminated.

I agree it is currently unclear whether the NULL termination is the responsibility of the __wasi_environ_get/__wasi_args_get syscalls, or of the calling code (i.e. the code in crt1.c).

[devsnek]

recently tripped me up as well while implementing this

[peterhuene]

Based on @sunfishcode's earlier comment, I think it's best to not force WASI into a convention that might be viewed as an implementation detail for a libc implementation.

I've put up #128 so we can discuss this further.