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Expand Up @@ -2,25 +2,31 @@

## Quick Start

[Download SDK packages here.](https://github.com/WebAssembly/wasi-sdk/releases)
[Download SDK packages here.][releases]

[releases]: https://github.com/WebAssembly/wasi-sdk/releases

## About this repository

This repository contains no compiler or library code itself; it uses
git submodules to pull in the upstream Clang and LLVM tree, as well as the
wasi-libc tree.

The libc portion of this SDK is the
[wasi-libc](https://github.com/WebAssembly/wasi-libc).
The libc portion of this SDK is maintained in [wasi-libc].

[wasi-libc]: https://github.com/WebAssembly/wasi-libc

Upstream Clang and LLVM (from 9.0 onwards) can compile for WASI out of the box,
and WebAssembly support is included in them by default. So, all that's done here
is to provide builds configured to set the default target and sysroot for
convenience.

One could also use a standard Clang installation, build a sysroot from the
sources mentioned above, and compile with
"--target=wasm32-wasi --sysroot=/path/to/sysroot".
sources mentioned above, and compile with `--target=wasm32-wasi
--sysroot=/path/to/sysroot`. In this scenario, one would also need the
`libclang_rt.builtins-wasm32.a` objects available separately in the [release
downloads][releases] which must be extracted into
`$CLANG_INSTALL_DIR/$CLANG_VERSION/lib/wasi/`.
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Actually, is this true? I know this is true for building wasi-libc (see building from source) from having to do this myself but is it the case for the average program?

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I'm not sure exactly what you mean.

If your question is "can you get away without libclang_rt.builtins-wasm32.a" then the answer is no. All programs pretty much end up depending on this library and clang adds it to the link line by default.

Also, wasi-libc is not a program (its just a static library) so technically you don't need libclang_rt.builtins-wasm32.a to build wasi-libc.. but in order to use wasi-libc in any kind of normal program, that is when you would need the builtins library (i.e. when you actually want to link something).

Or did I misunderstand your question?

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Ok, yeah, your response makes sense:

If your question is "can you get away without libclang_rt.builtins-wasm32.a" then the answer is no

That's what I thought but I started to confuse myself. So the language I'm using here does make sense: we need the builtins to just use vanilla Clang — it isn't as easy as "just point to a sysroot" as we previously had documented here.

Separately,

technically you don't need libclang_rt.builtins-wasm32.a to build wasi-libc

But the "we need the builtins" is documented in the wasi-libc instructions; maybe we should discuss that in WebAssembly/wasi-libc#425?


## Clone

Expand Down Expand Up @@ -57,7 +63,7 @@ version of the package on GitHub, see [RELEASING.md](RELEASING.md).
A typical installation from the release binaries might look like the following:

```shell script
export WASI_VERSION=14
export WASI_VERSION=20
export WASI_VERSION_FULL=${WASI_VERSION}.0
wget https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-${WASI_VERSION}/wasi-sdk-${WASI_VERSION_FULL}-linux.tar.gz
tar xvf wasi-sdk-${WASI_VERSION_FULL}-linux.tar.gz
Expand All @@ -75,24 +81,28 @@ $CC foo.c -o foo.wasm

Note: `${WASI_SDK_PATH}/share/wasi-sysroot` contains the WASI-specific
includes/libraries/etc. The `--sysroot=...` option is not necessary if
`WASI_SDK_PATH` is `/opt/wasi-sdk`.
`WASI_SDK_PATH` is `/opt/wasi-sdk`. For troubleshooting, one can replace the
`--sysroot` path with a manual build of [wasi-libc].

## Notes for Autoconf

[Autoconf](https://www.gnu.org/software/autoconf/autoconf.html) 2.70 now
[recognizes WASI](https://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=blob;f=build-aux/config.sub;h=19c9553b1825cafb182115513bc628e0ee801bd0;hb=97fbc5c184acc6fa591ad094eae86917f03459fa#l1723).
[Autoconf] 2.70 now [recognizes WASI].

[Autoconf]: https://www.gnu.org/software/autoconf/autoconf.html
[recognizes WASI]: https://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=blob;f=build-aux/config.sub;h=19c9553b1825cafb182115513bc628e0ee801bd0;hb=97fbc5c184acc6fa591ad094eae86917f03459fa#l1723

For convenience when building packages that aren't yet updated, updated
config.sub and config.guess files are installed at `share/misc/config.*`
in the install directory.

## Docker Image

We provide a [docker image](https://github.com/WebAssembly/wasi-sdk/pkgs/container/wasi-sdk)
including wasi-sdk that can be used for building projects without a
separate installation of the SDK. Autotools, CMake, and Ninja are included
in this image, and standard environment variables are set to use wask-sdk
for building.
We provide a [docker image] including wasi-sdk that can be used for building
projects without a separate installation of the SDK. Autotools, CMake, and Ninja
are included in this image, and standard environment variables are set to use
wask-sdk for building.

[docker image]: https://github.com/WebAssembly/wasi-sdk/pkgs/container/wasi-sdk

For example, this command can build a make-based project with the Docker
image.
Expand All @@ -107,24 +117,26 @@ disabled in a configure step before building with wasi-sdk.

## Notable Limitations

This repository does not yet support C++ exceptions. C++ code is
supported only with -fno-exceptions for now. Similarly, there is not
yet support for setjmp/longjmp. Work on support for [exception handling]
is underway at the language level which will support both of these
features.
This repository does not yet support __C++ exceptions__. C++ code is supported
only with -fno-exceptions for now. Similarly, there is not yet support for
setjmp/longjmp. Work on support for [exception handling] is underway at the
language level which will support both of these features.

[exception handling]: https://github.com/WebAssembly/exception-handling/

This repository does not yet support [threads]. Specifically, WASI does
not yet have an API for creating and managing threads yet, and WASI libc
does not yet have pthread support.
This repository experimentally supports __threads__ with
`--target=wasm32-wasi-threads`. It uses WebAssembly's [threads] primitives
(atomics, `wait`/`notify`, shared memory) and [wasi-threads] for spawning
threads. Note: this is experimental — do not expect long-term stability!

[threads]: https://github.com/WebAssembly/threads
[wasi-threads]: https://github.com/WebAssembly/wasi-threads

This repository does not yet support __dynamic libraries__. While there are
[some efforts] to design a system for dynamic libraries in wasm, it is still in
development and not yet generally usable.

This repository does not yet support dynamic libraries. While there are
[some efforts](https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md)
to design a system for dynamic libraries in wasm, it is still in development
and not yet generally usable.
[some efforts]: https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md

There is no support for networking. It is a goal of WASI to support networking
in the future though.
There is no support for __networking__. It is a goal of WASI to support
networking in the future though.