Add #[inline] to RawWaker::new
`RawWaker::new` is used when creating a new waker or cloning an existing one,
for example as in code below. The `RawWakerVTable::new` can be const evaluated,
but `RawWaker::new` itself cannot since waker pointer is not known at compile
time. Add `#[inline]` to avoid overhead of a function call.
```rust
unsafe fn clone_waker<W: Wake + Send + Sync + 'static>(waker: *const ()) -> RawWaker {
unsafe { Arc::incr_strong_count(waker as *const W) };
RawWaker::new(
waker as *const (),
&RawWakerVTable::new(clone_waker::<W>, wake::<W>, wake_by_ref::<W>, drop_waker::<W>),
)
}
```
This commit is a proof-of-concept for switching the standard library's
backtrace symbolication mechanism on most platforms from libbacktrace to
gimli. The standard library's support for `RUST_BACKTRACE=1` requires
in-process parsing of object files and DWARF debug information to
interpret it and print the filename/line number of stack frames as part
of a backtrace.
Historically this support in the standard library has come from a
library called "libbacktrace". The libbacktrace library seems to have
been extracted from gcc at some point and is written in C. We've had a
lot of issues with libbacktrace over time, unfortunately, though. The
library does not appear to be actively maintained since we've had
patches sit for months-to-years without comments. We have discovered a
good number of soundness issues with the library itself, both when
parsing valid DWARF as well as invalid DWARF. This is enough of an issue
that the libs team has previously decided that we cannot feed untrusted
inputs to libbacktrace. This also doesn't take into account the
portability of libbacktrace which has been difficult to manage and
maintain over time. While possible there are lots of exceptions and it's
the main C dependency of the standard library right now.
For years it's been the desire to switch over to a Rust-based solution
for symbolicating backtraces. It's been assumed that we'll be using the
Gimli family of crates for this purpose, which are targeted at safely
and efficiently parsing DWARF debug information. I've been working
recently to shore up the Gimli support in the `backtrace` crate. As of a
few weeks ago the `backtrace` crate, by default, uses Gimli when loaded
from crates.io. This transition has gone well enough that I figured it
was time to start talking seriously about this change to the standard
library.
This commit is a preview of what's probably the best way to integrate
the `backtrace` crate into the standard library with the Gimli feature
turned on. While today it's used as a crates.io dependency, this commit
switches the `backtrace` crate to a submodule of this repository which
will need to be updated manually. This is not done lightly, but is
thought to be the best solution. The primary reason for this is that the
`backtrace` crate needs to do some pretty nontrivial filesystem
interactions to locate debug information. Working without `std::fs` is
not an option, and while it might be possible to do some sort of
trait-based solution when prototyped it was found to be too unergonomic.
Using a submodule allows the `backtrace` crate to build as a submodule
of the `std` crate itself, enabling it to use `std::fs` and such.
Otherwise this adds new dependencies to the standard library. This step
requires extra attention because this means that these crates are now
going to be included with all Rust programs by default. It's important
to note, however, that we're already shipping libbacktrace with all Rust
programs by default and it has a bunch of C code implementing all of
this internally anyway, so we're basically already switching
already-shipping functionality to Rust from C.
* `object` - this crate is used to parse object file headers and
contents. Very low-level support is used from this crate and almost
all of it is disabled. Largely we're just using struct definitions as
well as convenience methods internally to read bytes and such.
* `addr2line` - this is the main meat of the implementation for
symbolication. This crate depends on `gimli` for DWARF parsing and
then provides interfaces needed by the `backtrace` crate to turn an
address into a filename / line number. This crate is actually pretty
small (fits in a single file almost!) and mirrors most of what
`dwarf.c` does for libbacktrace.
* `miniz_oxide` - the libbacktrace crate transparently handles
compressed debug information which is compressed with zlib. This crate
is used to decompress compressed debug sections.
* `gimli` - not actually used directly, but a dependency of `addr2line`.
* `adler32`- not used directly either, but a dependency of
`miniz_oxide`.
The goal of this change is to improve the safety of backtrace
symbolication in the standard library, especially in the face of
possibly malformed DWARF debug information. Even to this day we're still
seeing segfaults in libbacktrace which could possibly become security
vulnerabilities. This change should almost entirely eliminate this
possibility whilc also paving the way forward to adding more features
like split debug information.
Some references for those interested are:
* Original addition of libbacktrace - #12602
* OOM with libbacktrace - #24231
* Backtrace failure due to use of uninitialized value - #28447
* Possibility to feed untrusted data to libbacktrace - #21889
* Soundness fix for libbacktrace - #33729
* Crash in libbacktrace - #39468
* Support for macOS, never merged - ianlancetaylor/libbacktrace#2
* Performance issues with libbacktrace - #29293, #37477
* Update procedure is quite complicated due to how many patches we
need to carry - #50955
* Libbacktrace doesn't work on MinGW with dynamic libs - #71060
* Segfault in libbacktrace on macOS - #71397
Switching to Rust will not make us immune to all of these issues. The
crashes are expected to go away, but correctness and performance may
still have bugs arise. The gimli and `backtrace` crates, however, are
actively maintained unlike libbacktrace, so this should enable us to at
least efficiently apply fixes as situations come up.
Update stdarch submodule
This commit updates the src/stdarch submodule primarily to include
rust-lang/stdarch#874 which updated and revamped WebAssembly SIMD
intrinsics and renamed WebAssembly atomics intrinsics. This is all
unstable surface area of the standard library so the changes should be
ok here. The SIMD updates also enable SIMD intrinsics to be used by any
program any any time, yay!
cc #74372, a tracking issue I've opened for the stabilization of SIMD
intrinsics
This commit improves code generation for WebAssembly targets when
translating floating to integer casts. This improvement is only relevant
when the `nontrapping-fptoint` feature is not enabled, but the feature
is not enabled by default right now. Additionally this improvement only
affects safe casts since unchecked casts were improved in #74659.
Some more background for this issue is present on #73591, but the
general gist of the issue is that in LLVM the `fptosi` and `fptoui`
instructions are defined to return an `undef` value if they execute on
out-of-bounds values; they notably do not trap. To implement these
instructions for WebAssembly the LLVM backend must therefore generate
quite a few instructions before executing `i32.trunc_f32_s` (for
example) because this WebAssembly instruction traps on out-of-bounds
values. This codegen into wasm instructions happens very late in the
code generator, so what ends up happening is that rustc inserts its own
codegen to implement Rust's saturating semantics, and then LLVM also
inserts its own codegen to make sure that the `fptosi` instruction
doesn't trap. Overall this means that a function like this:
#[no_mangle]
pub unsafe extern "C" fn cast(x: f64) -> u32 {
x as u32
}
will generate this WebAssembly today:
(func $cast (type 0) (param f64) (result i32)
(local i32 i32)
local.get 0
f64.const 0x1.fffffffep+31 (;=4.29497e+09;)
f64.gt
local.set 1
block ;; label = @1
block ;; label = @2
local.get 0
f64.const 0x0p+0 (;=0;)
local.get 0
f64.const 0x0p+0 (;=0;)
f64.gt
select
local.tee 0
f64.const 0x1p+32 (;=4.29497e+09;)
f64.lt
local.get 0
f64.const 0x0p+0 (;=0;)
f64.ge
i32.and
i32.eqz
br_if 0 (;@2;)
local.get 0
i32.trunc_f64_u
local.set 2
br 1 (;@1;)
end
i32.const 0
local.set 2
end
i32.const -1
local.get 2
local.get 1
select)
This PR improves the situation by updating the code generation for
float-to-int conversions in rustc, specifically only for WebAssembly
targets and only for some situations (float-to-u8 still has not great
codegen). The fix here is to use basic blocks and control flow to avoid
speculatively executing `fptosi`, and instead LLVM's raw intrinsic for
the WebAssembly instruction is used instead. This effectively extends
the support added in #74659 to checked casts. After this commit the
codegen for the above Rust function looks like:
(func $cast (type 0) (param f64) (result i32)
(local i32)
block ;; label = @1
local.get 0
f64.const 0x0p+0 (;=0;)
f64.ge
local.tee 1
i32.const 1
i32.xor
br_if 0 (;@1;)
local.get 0
f64.const 0x1.fffffffep+31 (;=4.29497e+09;)
f64.le
i32.eqz
br_if 0 (;@1;)
local.get 0
i32.trunc_f64_u
return
end
i32.const -1
i32.const 0
local.get 1
select)
For reference, in Rust 1.44, which did not have saturating
float-to-integer casts, the codegen LLVM would emit is:
(func $cast (type 0) (param f64) (result i32)
block ;; label = @1
local.get 0
f64.const 0x1p+32 (;=4.29497e+09;)
f64.lt
local.get 0
f64.const 0x0p+0 (;=0;)
f64.ge
i32.and
i32.eqz
br_if 0 (;@1;)
local.get 0
i32.trunc_f64_u
return
end
i32.const 0)
So we're relatively close to the original codegen, although it's
slightly different because the semantics of the function changed where
we're emulating the `i32.trunc_sat_f32_s` instruction rather than always
replacing out-of-bounds values with zero.
There is still work that could be done to improve casts such as `f32` to
`u8`. That form of cast still uses the `fptosi` instruction which
generates lots of branch-y code. This seems less important to tackle now
though. In the meantime this should take care of most use cases of
floating-point conversion and as a result I'm going to speculate that
this...
Closes#73591
This commit updates the src/stdarch submodule primarily to include
rust-lang/stdarch#874 which updated and revamped WebAssembly SIMD
intrinsics and renamed WebAssembly atomics intrinsics. This is all
unstable surface area of the standard library so the changes should be
ok here. The SIMD updates also enable SIMD intrinsics to be used by any
program any any time, yay!
cc #74372, a tracking issue I've opened for the stabilization of SIMD
intrinsics
Improve defaults in x.py
- Make the default stage dependent on the subcommand
- Don't build stage1 rustc artifacts with x.py build --stage 1. If this is what you want, use x.py build --stage 2 instead, which gives you a working libstd.
- Change default debuginfo when debug = true from 2 to 1
I tried to fix CI to use `--stage 2` everywhere it currently has no stage, but I might have missed a spot.
This does not update much of the documentation - most of it is in https://github.com/rust-lang/rustc-dev-guide/ or https://github.com/rust-lang/rust-forge and will need a separate PR.
See individual commits for a detailed rationale of each change.
See also the MCP: https://github.com/rust-lang/compiler-team/issues/326
r? @Mark-Simulacrum , but anyone is free to give an opinion.
Add the rust-docs component to toolchain x86_64-unknown-linux-musl, which allows
people using rustup on their musl-based linux distribution to download the
rust-docs.
config.toml.example: Update remap-debuginfo doc to be more general & accurate
This makes it more obvious that the work-around to #74786 is actually correct, and a custom `--remap-path-prefix` isn't needed.
In fact the previous comment `/rustc/$hash/$crate` was wrong, it is not `$crate` but whatever path exists in the rustc source tree, so either `src/$crate` or `vendor/$crate`. I've fixed that as well to avoid future confusion.
Separate `missing_doc_code_examples` from intra-doc links
These two lints have no relation other than both being nightly-only.
This allows stabilizing intra-doc links without stabilizing `missing_doc_code_examples`.
Fixes one of the issues spotted by @ollie27 in https://github.com/rust-lang/rust/pull/74430#issuecomment-664693080.
r? @Manishearth
- Use stage 2 for makefile
- Move assert to builder
- Don't add an assert for --help
- Allow --stage 0 if passed explicitly
- Don't assert defaults during tests
Otherwise it's impossible to test the defaults!
From [a conversation in discord](https://discordapp.com/channels/442252698964721669/443151243398086667/719200989269327882):
> Linking seems to consume all available RAM, leading to the OS to swap memory to disk and slowing down everything in the process
Compiling itself doesn't seem to take up as much RAM, and I'm only looking to check whether a minimal testcase can be compiled by rustc, where the runtime performance isn't much of an issue
> do you have debug = true or debuginfo-level = 2 in config.toml?
> if so I think that results in over 2GB of debuginfo nowadays and is likely the culprit
> which might mean we're giving out bad advice :(
Anecdotally, this sped up my stage 1 build from 15 to 10 minutes.
This still adds line numbers, it only removes variable and type information.
- Improve wording for debuginfo description
Co-authored-by: Teymour Aldridge <42674621+teymour-aldridge@users.noreply.github.com>
- Set rustc to build only when explicitly asked for
This allows building the stage2 rustc artifacts, which nothing depends
on.
Previously the behavior was as follows (where stageN <-> stage(N-1) artifacts, except for stage0 libstd):
- `x.py build --stage 0`:
- stage0 libstd
- stage1 rustc (but without putting rustc in stage0/)
This leaves you without any rustc at all except for the beta compiler
(https://github.com/rust-lang/rust/issues/73519). This is never what you want.
- `x.py build --stage 1`:
- stage0 libstd
- stage1 rustc
- stage1 libstd
- stage1 rustdoc
- stage2 rustc
This leaves you with a broken stage2 rustc which doesn't even have
libcore and is effectively useless. Additionally, it compiles rustc
twice, which is not normally what you want.
- `x.py build --stage 2`:
- stage0 libstd
- stage1 rustc
- stage1 libstd
- stage2 rustc
- stage2 rustdoc and tools
This builds all tools in release mode. This is the correct usage for CI,
but takes far to long for development.
Now the behavior is as follows:
- `x.py build --stage 0`:
- stage0 libstd
This is suitable for contributors only working on the standard library,
as it means rustc never has to be compiled.
- `x.py build --stage 1`:
- stage0 libstd
- stage1 rustc
- stage1 libstd
- stage1 rustdoc
This is suitable for contributors working on the compiler. It ensures
that you have a working rustc and libstd without having to pass
`src/libstd` in addition.
- `x.py build --stage 2`:
- stage0 libstd
- stage1 rustc
- stage1 libstd
- stage2 rustc
- stage2 libstd
- stage2 rustdoc
This is suitable for debugging errors which only appear with the stage2
compiler.
- `x.py build --stage 2 src/libstd src/rustc`
- stage0 libstd
- stage1 rustc
- stage1 libstd
- stage2 rustc
- stage2 libstd
- stage2 rustdoc, tools, etc.
- stage2 rustc artifacts ('stage3')
This is suitable for CI, which wants all tools in release mode.
However, most of the use cases for this should use `x.py dist` instead,
which builds all the tools without each having to be named individually.
### x.py build/test: stage 1
I've seen very few people who actually use full stage 2 builds on purpose. These compile rustc and libstd twice and don't give you much more information than a stage 1 build (except in rare cases like https://github.com/rust-lang/rust/pull/68692#discussion_r376392145). For new contributors, this makes the build process even more daunting than it already is. As long as CI is changed to use `--stage 2` I see no downside here.
### x.py bench/dist/install: stage 2
These commands have to do with a finished, optimized version of rustc. It seems very rare to want to use these with a stage 1 build.
### x.py doc: stage 0
Normally when you document things you're just fixing a typo. In this case there is no need to build the whole rust compiler, since the documentation will usually be the same when generated with the beta compiler or with stage 1.
Note that for this release cycle only there will be a significant different between stage0 and stage1 docs: https://github.com/rust-lang/rust/pull/73101. However most of the time this will not be the case.
