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bors 709b72e7a7 Auto merge of #59464 - alexcrichton:wasi-pr, r=fitzgen Add a new wasm32-unknown-wasi target This commit adds a new wasm32-based target distributed through rustup, supported in the standard library, and implemented in the compiler. The `wasm32-unknown-wasi` target is intended to be a WebAssembly target which matches the [WASI proposal recently announced][LINK]. In summary the WASI target is an effort to define a standard set of syscalls for WebAssembly modules, allowing WebAssembly modules to not only be portable across architectures but also be portable across environments implementing this standard set of system calls. The wasi target in libstd is still somewhat bare bones. This PR does not fill out the filesystem, networking, threads, etc. Instead it only provides the most basic of integration with the wasi syscalls, enabling features like: * `Instant::now` and `SystemTime::now` work * `env::args` is hooked up * `env::vars` will look up environment variables * `println!` will print to standard out * `process::{exit, abort}` should be hooked up appropriately None of these APIs can work natively on the `wasm32-unknown-unknown` target, but with the assumption of the WASI set of syscalls we're able to provide implementations of these syscalls that engines can implement. Currently the primary engine implementing wasi is [wasmtime], but more will surely emerge! In terms of future development of libstd, I think this is something we'll probably want to discuss. The purpose of the WASI target is to provide a standardized set of syscalls, but it's also to provide a standard C sysroot for compiling C/C++ programs. This means it's intended that functions like `read` and `write` are implemented for this target with a relatively standard definition and implementation. It's unclear, therefore, how we want to expose file descriptors and how we'll want to implement system primitives. For example should `std::fs::File` have a libc-based file descriptor underneath it? The raw wasi file descriptor? We'll see! Currently these details are all intentionally hidden and things we can change over time. A `WasiFd` sample struct was added to the standard library as part of this commit, but it's not currently used. It shows how all the wasi syscalls could be ergonomically bound in Rust, and they offer a possible implementation of primitives like `std::fs::File` if we bind wasi file descriptors exactly. Apart from the standard library, there's also the matter of how this target is integrated with respect to its C standard library. The reference sysroot, for example, provides managment of standard unix file descriptors and also standard APIs like `open` (as opposed to the relative `openat` inspiration for the wasi ssycalls). Currently the standard library relies on the C sysroot symbols for operations such as environment management, process exit, and `read`/`write` of stdio fds. We want these operations in Rust to be interoperable with C if they're used in the same process. Put another way, if Rust and C are linked into the same WebAssembly binary they should work together, but that requires that the same C standard library is used. We also, however, want the `wasm32-unknown-wasi` target to be usable-by-default with the Rust compiler without requiring a separate toolchain to get downloaded and configured. With that in mind, there's two modes of operation for the `wasm32-unknown-wasi` target: 1. By default the C standard library is statically provided inside of `liblibc.rlib` distributed as part of the sysroot. This means that you can `rustc foo.wasm --target wasm32-unknown-unknown` and you're good to go, a fully workable wasi binary pops out. This is incompatible with linking in C code, however, which may be compiled against a different sysroot than the Rust code was previously compiled against. In this mode the default of `rust-lld` is used to link binaries. 2. For linking with C code, the `-C target-feature=-crt-static` flag needs to be passed. This takes inspiration from the musl target for this flag, but the idea is that you're no longer using the provided static C runtime, but rather one will be provided externally. This flag is intended to also get coupled with an external `clang` compiler configured with its own sysroot. Therefore you'll typically use this flag with `-C linker=/path/to/clang-script-wrapper`. Using this mode the Rust code will continue to reference standard C symbols, but the definition will be pulled in by the linker configured. Alright so that's all the current state of this PR. I suspect we'll definitely want to discuss this before landing of course! This PR is coupled with libc changes as well which I'll be posting shortly. [LINK]: https://hacks.mozilla.org/2019/03/standardizing-wasi-a-webassembly-system-interface/ [wasmtime]: https://github.com/cranestation/wasmtime-wasi		2019-03-30 02:34:13 +00:00
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README.md

The Rust Programming Language

This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.

Quick Start

Read "Installation" from The Book.

Installing from Source

Note: If you wish to contribute to the compiler, you should read this chapter of the rustc-guide instead.

Building on *nix

Make sure you have installed the dependencies:
- g++ 4.7 or later or clang++ 3.x or later
- python 2.7 (but not 3.x)
- GNU make 3.81 or later
- cmake 3.4.3 or later
- curl
- git

Clone the source with git:

$ git clone https://github.com/rust-lang/rust.git
$ cd rust

Build and install:
```
$ ./x.py build && sudo ./x.py install
```
If after running sudo ./x.py install you see an error message like
```
error: failed to load source for a dependency on 'cc'
```
then run these two commands and then try sudo ./x.py install again:
```
$ cargo install cargo-vendor
```
```
$ cargo vendor
```
Note: Install locations can be adjusted by copying the config file from ./config.toml.example to ./config.toml, and adjusting the prefix option under [install]. Various other options, such as enabling debug information, are also supported, and are documented in the config file.

When complete, sudo ./x.py install will place several programs into /usr/local/bin: rustc, the Rust compiler, and rustdoc, the API-documentation tool. This install does not include Cargo, Rust's package manager, which you may also want to build.

Building on Windows

There are two prominent ABIs in use on Windows: the native (MSVC) ABI used by Visual Studio, and the GNU ABI used by the GCC toolchain. Which version of Rust you need depends largely on what C/C++ libraries you want to interoperate with: for interop with software produced by Visual Studio use the MSVC build of Rust; for interop with GNU software built using the MinGW/MSYS2 toolchain use the GNU build.

MinGW

MSYS2 can be used to easily build Rust on Windows:

Grab the latest MSYS2 installer and go through the installer.
Run mingw32_shell.bat or mingw64_shell.bat from wherever you installed MSYS2 (i.e. C:\msys64), depending on whether you want 32-bit or 64-bit Rust. (As of the latest version of MSYS2 you have to run msys2_shell.cmd -mingw32 or msys2_shell.cmd -mingw64 from the command line instead)

From this terminal, install the required tools:

# Update package mirrors (may be needed if you have a fresh install of MSYS2)
$ pacman -Sy pacman-mirrors

# Install build tools needed for Rust. If you're building a 32-bit compiler,
# then replace "x86_64" below with "i686". If you've already got git, python,
# or CMake installed and in PATH you can remove them from this list. Note
# that it is important that you do **not** use the 'python2' and 'cmake'
# packages from the 'msys2' subsystem. The build has historically been known
# to fail with these packages.
$ pacman -S git \
            make \
            diffutils \
            tar \
            mingw-w64-x86_64-python2 \
            mingw-w64-x86_64-cmake \
            mingw-w64-x86_64-gcc

Navigate to Rust's source code (or clone it), then build it:
```
$ ./x.py build && ./x.py install
```

MSVC

MSVC builds of Rust additionally require an installation of Visual Studio 2013 (or later) so rustc can use its linker. Make sure to check the “C++ tools” option.

With these dependencies installed, you can build the compiler in a cmd.exe shell with:

> python x.py build

Currently, building Rust only works with some known versions of Visual Studio. If you have a more recent version installed the build system doesn't understand then you may need to force rustbuild to use an older version. This can be done by manually calling the appropriate vcvars file before running the bootstrap.

> CALL "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\amd64\vcvars64.bat"
> python x.py build

Specifying an ABI

Each specific ABI can also be used from either environment (for example, using the GNU ABI in PowerShell) by using an explicit build triple. The available Windows build triples are:

GNU ABI (using GCC)
- i686-pc-windows-gnu
- x86_64-pc-windows-gnu
The MSVC ABI
- i686-pc-windows-msvc
- x86_64-pc-windows-msvc

The build triple can be specified by either specifying --build=<triple> when invoking x.py commands, or by copying the config.toml file (as described in Building From Source), and modifying the build option under the [build] section.

Configure and Make

While it's not the recommended build system, this project also provides a configure script and makefile (the latter of which just invokes x.py).

$ ./configure
$ make && sudo make install

When using the configure script, the generated config.mk file may override the config.toml file. To go back to the config.toml file, delete the generated config.mk file.

Building Documentation

If you’d like to build the documentation, it’s almost the same:

$ ./x.py doc

The generated documentation will appear under doc in the build directory for the ABI used. I.e., if the ABI was x86_64-pc-windows-msvc, the directory will be build\x86_64-pc-windows-msvc\doc.

Notes

Since the Rust compiler is written in Rust, it must be built by a precompiled "snapshot" version of itself (made in an earlier stage of development). As such, source builds require a connection to the Internet, to fetch snapshots, and an OS that can execute the available snapshot binaries.

Snapshot binaries are currently built and tested on several platforms:

Platform / Architecture	x86	x86_64
Windows (7, 8, 10, ...)	✓	✓
Linux (2.6.18 or later)	✓	✓
OSX (10.7 Lion or later)	✓	✓

You may find that other platforms work, but these are our officially supported build environments that are most likely to work.

There is more advice about hacking on Rust in CONTRIBUTING.md.

Getting Help

The Rust community congregates in a few places:

Stack Overflow - Direct questions about using the language.
users.rust-lang.org - General discussion and broader questions.
/r/rust - News and general discussion.

Contributing

To contribute to Rust, please see CONTRIBUTING.

Rust has an IRC culture and most real-time collaboration happens in a variety of channels on Mozilla's IRC network, irc.mozilla.org. The most popular channel is #rust, a venue for general discussion about Rust. And a good place to ask for help would be #rust-beginners.

The rustc guide might be a good place to start if you want to find out how various parts of the compiler work.

Also, you may find the rustdocs for the compiler itself useful.

License

Rust is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.

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