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bors 6846f22a13 Auto merge of #51946 - japaric:emit-stack-sizes, r=nikomatsakis 
[eRFC] add -Z emit-stack-sizes

# What

This PR exposes LLVM's ability to report the stack usage of each function through the unstable /
experimental `-Z emit-stack-sizes` flag.

# Motivation

The end goal is to enable whole program analysis of stack usage to prove absence of stack overflows
at compile time. Such property is important in systems that lack a MMU / MPU and where stack
overflows can corrupt memory. And in systems that have protection against stack overflows such proof
can be used to opt out of runtime checks (e.g. stack probes or the MPU).

Such analysis requires the call graph of the program, which can be obtained from MIR, and the stack
usage of each function in the program. Precise information about the later later can only be
obtained from LLVM as it depends on the optimization level and optimization options like LTO.

This PR does **not** attempt to add the ability to perform such whole program analysis to rustc;
it simply does the minimal amount of work to enable such analysis to be implemented out of tree.

# Implementation

This PR exposes a way to set LLVM's `EmitStackSizeSection` option from the command line. The option
is documented [here]; the documentation is copied below for convenience and posteriority:

[here]: https://llvm.org/docs/CodeGenerator.html#emitting-function-stack-size-information

> A section containing metadata on function stack sizes will be emitted when
> TargetLoweringObjectFile::StackSizesSection is not null, and TargetOptions::EmitStackSizeSection
> is set (-stack-size-section). The section will contain an array of pairs of function symbol values
> (pointer size) and stack sizes (unsigned LEB128). The stack size values only include the space
> allocated in the function prologue. Functions with dynamic stack allocations are not included.

Where the LLVM feature is not available (e.g. LLVM version < 6.0) or can't be applied (e.g. the
output format doesn't support sections e.g. .wasm files) the flag does nothing -- i.e. no error or
warning is emitted.

# Example usage

``` console
$ cargo new --bin hello && cd $_

$ cat >src/main.rs <<'EOF'
use std::{mem, ptr};

fn main() {
    registers();
    stack();
}

#[inline(never)]
fn registers() {
    unsafe {
        // values loaded into registers
        ptr::read_volatile(&(0u64, 1u64));
    }
}

#[inline(never)]
fn stack() {
    unsafe {
        // array allocated on the stack
        let array: [i32; 4] = mem::uninitialized();
        for elem in &array {
            ptr::read_volatile(&elem);
        }
    }
}
EOF

$ # we need a custom linking step to preserve the .stack_sizes section
$ # (see unresolved questions for a solution that doesn't require custom linking)
$ cat > keep-stack-sizes.x <<'EOF'
SECTIONS
{
  .stack_sizes :
  {
    KEEP(*(.stack_sizes));
  }
}
EOF

$ cargo rustc --release -- \
    -Z emit-stack-sizes \
    -C link-arg=-Wl,-Tkeep-stack-sizes.x \
    -C link-arg=-N

$ size -A target/release/hello | grep stack_sizes
.stack_sizes    117   185136
```

Then a tool like [`stack-sizes`] can be used to print the information in human readable format

[`stack-sizes`]: https://github.com/japaric/stack-sizes/#stack-sizes

``` console
$ stack-sizes target/release/hello
address                 size    name
0x000000000004b0        0       core::array::<impl core::iter::traits::IntoIterator for &'a [T; _]>::into_iter::ha50e6661c0ec84aa
0x000000000004c0        8       std::rt::lang_start::ha02aea783e0e1b3e
0x000000000004f0        8       std::rt::lang_start::{{closure}}::h5115b527d5244952
0x00000000000500        8       core::ops::function::FnOnce::call_once::h6bfa1076da82b0fb
0x00000000000510        0       core::ptr::drop_in_place::hb4de82e57787bc70
0x00000000000520        8       hello::main::h08bb6cec0556bd66
0x00000000000530        0       hello::registers::h9d058a5d765ec1d2
0x00000000000540        24      hello::stack::h88c8cb66adfdc6f3
0x00000000000580        8       main
0x000000000005b0        0       __rust_alloc
0x000000000005c0        0       __rust_dealloc
0x000000000005d0        0       __rust_realloc
0x000000000005e0        0       __rust_alloc_zeroed
```

# Stability

Like `-Z sanitize` this is a re-export of an LLVM feature. To me knowledge, we don't have a policy
about stabilization of such features as they are incompatible with, or demand extra implementation
effort from, alternative backends (e.g. cranelift). As such this feature will remain experimental /
unstable for the foreseeable future.

# Unresolved questions

## Section name

Should we rename the `.stack_sizes` section to `.debug_stacksizes`?

With the former name linkers will strip the section unless told otherwise using a linker script,
which means getting this information requires both knowledge about linker scripts and a custom
linker invocation (see example above).

If we use the `.debug_stacksizes` name (I believe) linkers will always keep the section, which means
`-Z emit-stack-sizes` is the only thing required to get the stack usage information.

# ~TODOs~

~Investigate why this doesn't work with the `thumb` targets. I get the LLVM error shown below:~

``` console
$ cargo new --lib foo && cd $_

$ echo '#![no_std] pub fn foo() {}' > src/lib.rs

$ cargo rustc --target thumbv7m-none-eabi -- -Z emit-stack-sizes
LLVM ERROR: unsupported relocation on symbol
```

~which sounds like it might be related to the `relocation-model` option. Maybe `relocation-model =
static` is not supported for some reason?~

This fixed itself after the LLVM upgrade.

---

r? @nikomatsakis
cc @rust-lang/compiler @perlindgren @whitequark
2018-09-26 15:40:37 +00:00
src Auto merge of #51946 - japaric:emit-stack-sizes, r=nikomatsakis 2018-09-26 15:40:37 +00:00
.gitattributes Mark .fixed files as Rust syntax for GitHub 2018-05-28 11:36:13 +02:00
.gitignore move file-extension based .gitignore down to src/ 2018-08-28 20:04:52 +02:00
.gitmodules Merge branch 'master' into fix-submodules 2018-09-05 21:40:39 -07:00
.mailmap Update .mailmap 2018-09-21 14:02:45 -05:00
.travis.yml Pass --batch to gdb 2018-09-19 09:46:22 -06:00
appveyor.yml Migrate the toolstate update bot to rust-highfive 2018-05-14 22:34:53 +08:00
CODE_OF_CONDUCT.md Synchronizing with code of conduct in rust-www 2018-03-07 08:58:57 -08:00
config.toml.example Improvements to finding LLVM's FileCheck 2018-09-25 09:13:02 -06:00
configure rustbuild: Rewrite the configure script in Python 2017-08-27 18:53:30 -07:00
CONTRIBUTING.md COMPILER_TESTS.md has been moved 2018-09-12 21:21:43 -07:00
COPYRIGHT Remove references to AUTHORS.txt file 2018-07-30 07:47:12 +02:00
LICENSE-APACHE Update license, add license boilerplate to most files. Remainder will follow. 2012-12-03 17:12:14 -08:00
LICENSE-MIT LICENSE-MIT: Remove inaccurate (misattributed) copyright notice 2017-07-26 16:51:58 -07:00
README.md docs: Use dollar sign for all bash prompts 2018-09-08 21:22:00 -07:00
RELEASES.md Rollup merge of #54150 - Aaronepower:master, r=Mark-Simulacrum 2018-09-14 00:41:53 +08:00
x.py Rename os variable in bootstrap.py to avoid shadowing os module. 2017-04-30 16:10:31 -04:00

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.

Building from Source

Building on *nix

  1. 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

  2. Clone the source with git:

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

  1. Build and install:

    $ git submodule update --init --recursive --progress
$ ./x.py build && sudo ./x.py install

    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:

  1. Grab the latest MSYS2 installer and go through the installer.

  2. 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)

  3. 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

  4. 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, Server 2008 R2) ✓ ✓
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.

Rust currently needs between 600MiB and 1.5GiB of RAM to build, depending on platform. If it hits swap, it will take a very long time to build.

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

Getting Help

The Rust community congregates in a few places:

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.

See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.