When taking the address of an unsized field we generate a rvalue datum
for the field and then convert it to an lvalue datum. At that point,
cleanup is scheduled for the field, leading to multiple drop calls.
The problem is that we generate an rvalue datum for the field, since the
pointer does not own the data and there's already cleanup scheduled
elsewhere by the true owner. Instead, an lvalue datum must be created.
Thanks to @eddyb for identifying the underlying cause and suggesting the
correct fix.
Fixes#25549.
Use stable code in doc examples (libcollections)
Main task is to change from String::from_str to String::from in examples for String
(the latter constructor is stable). While I'm at it, also remove redundant feature flags,
fix some other instances of unstable code in examples (in examples for stable
methods), and remove some use of usize in examples too.
Special thanks to @retep998 for the [excellent writeup](https://github.com/rust-lang/rfcs/issues/1061) of tasks to be done and @ricky26 for initially blazing the trail here!
# MSVC Support
This goal of this series of commits is to add MSVC support to the Rust compiler
and build system, allowing it more easily interoperate with Visual Studio
installations and native libraries compiled outside of MinGW.
The tl;dr; of this change is that there is a new target of the compiler,
`x86_64-pc-windows-msvc`, which will not interact with the MinGW toolchain at
all and will instead use `link.exe` to assemble output artifacts.
## Why try to use MSVC?
With today's Rust distribution, when you install a compiler on Windows you also
install `gcc.exe` and a number of supporting libraries by default (this can be
opted out of). This allows installations to remain independent of MinGW
installations, but it still generally requires native code to be linked with
MinGW instead of MSVC. Some more background can also be found in #1768 about the
incompatibilities between MinGW and MSVC.
Overall the current installation strategy is quite nice so long as you don't
interact with native code, but once you do the usage of a MinGW-based `gcc.exe`
starts to get quite painful.
Relying on a nonstandard Windows toolchain has also been a long-standing "code
smell" of Rust and has been slated for remedy for quite some time now. Using a
standard toolchain is a great motivational factor for improving the
interoperability of Rust code with the native system.
## What does it mean to use MSVC?
"Using MSVC" can be a bit of a nebulous concept, but this PR defines it as:
* The build system for Rust will build as much code as possible with the MSVC
compiler, `cl.exe`.
* The build system will use native MSVC tools for managing archives.
* The compiler will link all output with `link.exe` instead of `gcc.exe`.
None of these are currently implemented today, but all are required for the
compiler to fluently interoperate with MSVC.
## How does this all work?
At the highest level, this PR adds a new target triple to the Rust compiler:
x86_64-pc-windows-msvc
All logic for using MSVC or not is scoped within this triple and code can
conditionally build for MSVC or MinGW via:
#[cfg(target_env = "msvc")]
It is expected that auto builders will be set up for MSVC-based compiles in
addition to the existing MinGW-based compiles, and we will likely soon start
shipping MSVC nightlies where `x86_64-pc-windows-msvc` is the host target triple
of the compiler.
# Summary of changes
Here I'll explain at a high level what many of the changes made were targeted
at, but many more details can be found in the commits themselves. Many thanks to
@retep998 for the excellent writeup in rust-lang/rfcs#1061 and @rick26 for a lot
of the initial proof-of-concept work!
## Build system changes
As is probably expected, a large chunk of this PR is changes to Rust's build
system to build with MSVC. At a high level **it is an explicit non goal** to
enable building outside of a MinGW shell, instead all Makefile infrastructure we
have today is retrofitted with support to use MSVC instead of the standard MSVC
toolchain. Some of the high-level changes are:
* The configure script now detects when MSVC is being targeted and adds a number
of additional requirements about the build environment:
* The `--msvc-root` option must be specified or `cl.exe` must be in PATH to
discover where MSVC is installed. The compiler in use is also required to
target x86_64.
* Once the MSVC root is known, the INCLUDE/LIB environment variables are
scraped so they can be reexported by the build system.
* CMake is required to build LLVM with MSVC (and LLVM is also configured with
CMake instead of the normal configure script).
* jemalloc is currently unconditionally disabled for MSVC targets as jemalloc
isn't a hard requirement and I don't know how to build it with MSVC.
* Invocations of a C and/or C++ compiler are now abstracted behind macros to
appropriately call the underlying compiler with the correct format of
arguments, for example there is now a macro for "assemble an archive from
objects" instead of hard-coded invocations of `$(AR) crus liboutput.a ...`
* The output filenames for standard libraries such as morestack/compiler-rt are
now "more correct" on windows as they are shipped as `foo.lib` instead of
`libfoo.a`.
* Rust targets can now depend on native tools provided by LLVM, and as you'll
see in the commits the entire MSVC target depends on `llvm-ar.exe`.
* Support for custom arbitrary makefile dependencies of Rust targets has been
added. The MSVC target for `rustc_llvm` currently requires a custom `.DEF`
file to be passed to the linker to get further linkages to complete.
## Compiler changes
The modifications made to the compiler have so far largely been minor tweaks
here and there, mostly just adding a layer of abstraction over whether MSVC or a
GNU-like linker is being used. At a high-level these changes are:
* The section name for metadata storage in dynamic libraries is called `.rustc`
for MSVC-based platorms as section names cannot contain more than 8
characters.
* The implementation of `rustc_back::Archive` was refactored, but the
functionality has remained the same.
* Targets can now specify the default `ar` utility to use, and for MSVC this
defaults to `llvm-ar.exe`
* The building of the linker command in `rustc_trans:🔙:link` has been
abstracted behind a trait for the same code path to be used between GNU and
MSVC linkers.
## Standard library changes
Only a few small changes were required to the stadnard library itself, and only
for minor differences between the C runtime of msvcrt.dll and MinGW's libc.a
* Some function names for floating point functions have leading underscores, and
some are not present at all.
* Linkage to the `advapi32` library for crypto-related functions is now
explicit.
* Some small bits of C code here and there were fixed for compatibility with
MSVC's cl.exe compiler.
# Future Work
This commit is not yet a 100% complete port to using MSVC as there are still
some key components missing as well as some unimplemented optimizations. This PR
is already getting large enough that I wanted to draw the line here, but here's
a list of what is not implemented in this PR, on purpose:
## Unwinding
The revision of our LLVM submodule [does not seem to implement][llvm] does not
support lowering SEH exception handling on the Windows MSVC targets, so
unwinding support is not currently implemented for the standard library (it's
lowered to an abort).
[llvm]: https://github.com/rust-lang/llvm/blob/rust-llvm-2015-02-19/lib/CodeGen/Passes.cpp#L454-L461
It looks like, however, that upstream LLVM has quite a bit more support for SEH
unwinding and landing pads than the current revision we have, so adding support
will likely just involve updating LLVM and then adding some shims of our own
here and there.
## dllimport and dllexport
An interesting part of Windows which MSVC forces our hand on (and apparently
MinGW didn't) is the usage of `dllimport` and `dllexport` attributes in LLVM IR
as well as native dependencies (in C these correspond to
`__declspec(dllimport)`).
Whenever a dynamic library is built by MSVC it must have its public interface
specified by functions tagged with `dllexport` or otherwise they're not
available to be linked against. This poses a few problems for the compiler, some
of which are somewhat fundamental, but this commit alters the compiler to attach
the `dllexport` attribute to all LLVM functions that are reachable (e.g. they're
already tagged with external linkage). This is suboptimal for a few reasons:
* If an object file will never be included in a dynamic library, there's no need
to attach the dllexport attribute. Most object files in Rust are not destined
to become part of a dll as binaries are statically linked by default.
* If the compiler is emitting both an rlib and a dylib, the same source object
file is currently used but with MSVC this may be less feasible. The compiler
may be able to get around this, but it may involve some invasive changes to
deal with this.
The flipside of this situation is that whenever you link to a dll and you import
a function from it, the import should be tagged with `dllimport`. At this time,
however, the compiler does not emit `dllimport` for any declarations other than
constants (where it is required), which is again suboptimal for even more
reasons!
* Calling a function imported from another dll without using `dllimport` causes
the linker/compiler to have extra overhead (one `jmp` instruction on x86) when
calling the function.
* The same object file may be used in different circumstances, so a function may
be imported from a dll if the object is linked into a dll, but it may be
just linked against if linked into an rlib.
* The compiler has no knowledge about whether native functions should be tagged
dllimport or not.
For now the compiler takes the perf hit (I do not have any numbers to this
effect) by marking very little as `dllimport` and praying the linker will take
care of everything. Fixing this problem will likely require adding a few
attributes to Rust itself (feature gated at the start) and then strongly
recommending static linkage on Windows! This may also involve shipping a
statically linked compiler on Windows instead of a dynamically linked compiler,
but these sorts of changes are pretty invasive and aren't part of this PR.
## CI integration
Thankfully we don't need to set up a new snapshot bot for the changes made here as our snapshots are freestanding already, we should be able to use the same snapshot to bootstrap both MinGW and MSVC compilers (once a new snapshot is made from these changes).
I plan on setting up a new suite of auto bots which are testing MSVC configurations for now as well, for now they'll just be bootstrapping and not running tests, but once unwinding is implemented they'll start running all tests as well and we'll eventually start gating on them as well.
---
I'd love as many eyes on this as we've got as this was one of my first interactions with MSVC and Visual Studio, so there may be glaring holes that I'm missing here and there!
cc @retep998, @ricky26, @vadimcn, @klutzy
r? @brson
"Truth passes, success `panic!`s" seems to be a typo. The closest fix would be something like "Success passes, failure `panic!`s" but to me a "comparison failure" suggests that we couldn't compare the two values at all, not that we could successfully compare them and that the result was non-equality. So I opted to rewrite the paragraph a bit. If there's a better alternative please let me know.
r? @steveklabnik
Padding and alignment are often not implemented by types and can cause confusion in the user. Per discussion with @alexcrichton, here is my PR.
/cc https://github.com/rust-lang/time/issues/98
The paper from which this example was taken made the mistake of assuming that all five philosophers are men. This it is a hypothetical example—there are no actual philosophers eating 🍝—so there is no good reason to make this assumption. Since women make up about half of the human population, all things being equal, women should represent about half of the philosophers. However, because this mistake has stood since 1985, I have changed *all* of the pronouns to be female, to make up for lost time. If someone would like to revert this patch or switch to neutral pronouns after 30 years, feel free to set your alarm clock for 2045.
r? @steveklabnik, since this is a documentation change and was created after reading http://words.steveklabnik.com/ouroboros, where I noticed this mistake.
The paper from which this example was taken made the mistake of assuming
that all five philosophers are men. This is a hypothetical
example--there are no actual philosophers eating spaghetti--so there is
no good reason to make this assumption. Since women make up about half
of the human population, all things being equal, women should represent
about half of the philosophers. However, because this mistake has stood
since 1985, I have changed *all* of the pronouns to be female, to make
up for lost time. If someone would like to revert this patch or switch
to neutral pronouns after 30 years, feel free to set your alarm clock
for 2045.
This commits adds a method to the `std::process` module to get the process
identifier of the child as a `u32`. On Windows the underlying identifier is
already a `u32`, and on Unix the type is typically defined as `c_int` (`i32` for
almost all our supported platforms), but the actually pid is normally a small
positive number.
Eventually we may add functions to load information about a process based on its
identifier or the ability to terminate a process based on its identifier, but
for now this function should enable this sort of functionality to exist outside
the standard library.
This commit updates the `dist` target for MSVC to not build the mingw components
and to also ensure that the `llvm-ar.exe` binary is ferried along into the right
location for installs.
This commit adds a small non-generic non-inlineable shim function to
`rt::unwind::try` which the compiler can take care of for managing the exported
symbol instead of having to edit `src/rt/rust_try.ll`
This commit modifies the compiler to emit `dllexport` for all reachable
functions and data on MSVC targets, regardless of whether a dynamic library is
being created or not. More details can be found in the commit itself.
This function is imported across the DLL boundary by the libtest dynamic
library, so it has to be marked as dllexport somehow, and for now this is done
with an attribute on the function specifically.
At this time unwinding support is not implemented for MSVC as
`libgcc_s_seh-1.dll` is not available by default (and this is used on MinGW),
but this should be investigated soon. For now this change is just aimed at
getting the compiler far enough to bootstrap everything instead of successfully
running tests.
This commit refactors the `std::rt::unwind` module a bit to prepare for SEH
support eventually by moving all GCC-specific functionality to its own submodule
and defining the interface needed.
For imports of constants across DLLs to work on Windows it *requires* that the
import be marked with `dllimport` (unlike functions where the marker is
optional, but strongly recommended). This currently isn't working for importing
FFI constants across boundaries, however, so the one constant exported from
`rustc_llvm.dll` is now a function to be called instead.
Windows needs explicit exports of functions from DLLs but LLVM does not mention
any of its symbols as being export-able from a DLL. The compiler, however,
relies on being able to use LLVM symbols across DLL boundaries so we need to
force many of LLVM's symbols to be exported from `rustc_llvm.dll`. This commit
adds support for generation of a `rustc_llvm.def` file which is passed along to
the linker when generating `rustc_llvm.dll` which should keep all these symbols
exportable and usable.
This commit adds an implementation of the `Linker` trait which is used to drive
MSVC's `link.exe` support. Nothing too surprising here as it's mostly just
filling out the necessary tidbits here and there.
These libraries don't exist! The linker for MSVC is highly likely to not pass
`/NODEFAULTLIB` in which case the right standard library will automatically be
selected.
This commit was initially written to target either `ar` or `lib.exe` for MSVC,
but it ended up not needing `lib.exe` support after all. I would personally like
to refactor this to one day not invoke processes at all (but rather use the
`llvm-ar.cpp` file in LLVM as alibrary) so I chose to preserve this refactoring
to allow it to be easily done in the future.
It looks like section names in objects generated by `link.exe` are limited to at
most 8 characters in length, so shorten `.note.rustc` to just `.rustc`
The compiler will require that `llvm-ar.exe` be available for MSVC-targeting
builds (more comments on this soon), so this commit adds support for targets to
depend on LLVM tools. The `core` library for MSVC depends on `llvm-ar.exe` which
will be copied into place for the target before the compiler starts to run.
Note that these targets all depend on `llvm-config.exe` to ensure that they're
built before they're attempted to be copied.
This commit updates the rustllvm.mk file with the necessary flags and such to
build rustllvm.lib with cl.exe instead of gcc. Some comments can be found in the
commit itself.
It looks like compiler-rt has a cmake build sytem inside its source, but I have
been unable to figure out how to use it and actually build the right library.
For now this commit hard-wires MSVC-targeting builds of libcompiler-rt to
continue using `make` as the primary bulid system, but some frobbing of the
flags are necessary to ensure that the right compiler is used.
Currently the MSVC compilers don't have any cross prefixes and we're only able
to make an MSVC compiler with a cross compile, so just avoid this logic on msvc
for now.
We have a number of support C/C++ files in Rust that we link into the standard
library and other various locations, and these all need to be built with cl.exe
instead of gcc.exe when targeting MSVC. This commit adds helper macros for this
functionality to use different sets of programs/flags/invocations on MSVC than
on GNU-like platforms.
This commit modifies the makefiles to enable building LLVM with cmake and Visual
Studio to generate an LLVM that targets MSVC. Rust's configure script requires
cmake to be installed when targeting MSVC and will configure LLVM with cmake
instead of the normal `./configure` script LLVM provides. The build will then
run cmake to execute the build instead of the normal `make`.
Currently `make clean-llvm` isn't supported on MSVC as I can't figure out how to
run a "clean" target for the Visual Studio files.
This commit starts to add MSVC support to the ./configure script to enable the
build system to detect and build an MSVC target with the cl.exe compiler and
toolchain. The primary change here is a large sanity check when an MSVC target
is requested (and currently only `x86_64-pc-windows-msvc` is recognized).
When building an MSVC target, the configure script either requires the
`--msvc-root` argument or for `cl.exe` to be in `PATH`. It also requires that if
in the path `cl.exe` is the 64-bit version of the compiler.
Once detected the configure script will run the `vcvarsall.bat` script provided
by Visual Studio to learn about the `INCLUDE` and `LIB` variables needed by the
`cl.exe` compiler to run (the default include/lib paths for the
compiler/linker). These variables are then reexported when running `make` to
ensure that our own compiles are running the same toolchain.
The purpose of this detection and environment variable scraping is to avoid
requiring the build itself to be run inside of a `cmd.exe` shell but rather
allow it to run in the currently expected MinGW/MSYS shell.
