Proposal for porting D runtime to WebAssembly

[kinke]

On Friday, 3 January 2020 at 10:34:40 UTC, Sebastiaan Koppe wrote:
> You can track the work here: 
> https://github.com/skoppe/druntime/tree/wasm

I gave it a quick glance; looks pretty good, and like pretty much 
work. ;) - Thx.

The compiler should probably help a bit by firstly predefining a 
version `CRuntime_WASI` (either for all wasm targets, or for 
triples like wasm32-unknown-unknown-wasi) and secondly emitting 
TLS globals as regular globals for now, so that you don't have to 
add `__gshared` everywhere.

> - reals (probably are going to be unsupported)

It's probably just a matter of checking which type clang uses for 
C `long double` when targeting wasm, and making LDC use the same 
type.

> - wasi libc needs to be distributed (either in source and 
> compiled into wasm druntime) or statically linked

I'd prefer a static lib (and referencing that one via 
`-defaultlib=druntime-ldc,phobos2-ldc,wasi` in ldc2.conf's wasm 
section).
Building it via LDC CI for inclusion in (some?) prebuilt LDC 
packages is probably not that much of a hassle with a clang host 
compiler.

> once ldc-build-druntime works

If you need some CMake help (excluding C files etc.), 
https://github.com/ldc-developers/ldc/pull/2787 might have 
something useful.

> (_start is the wasm's equivalent of _Dmain)

Not really; _start (in libc) is used on Linux too, which sets up 
the C runtime, then calls C main, which calls druntime's 
_d_run_main which in turn calls _Dmain.