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.
intra-doc links: resolve modules in the type namespace
Fixes https://github.com/rust-lang/rust/issues/62830
Modules actually live in the type namespace, not all three, and it's not possible to clash a type with a module.
Fix Arc::as_ptr docs
As a non-native speaker I stumbled upon this, looked it up and couldn't find a phrase, so I made my own assumption that "in any way" was meant (which is the meaning I would've deduced anyway)
Move hir::Place to librustc_middle/hir
Needed to support https://github.com/rust-lang/project-rfc-2229/issues/7
Currently rustc_typeck depends on rustc_middle for definition TypeckTables, etc.
For supporting project-rfc-2229#7, rustc_middle would've to depend on
rustc_typeck for Place -- introducing a circular dependency.
This resembles the MIR equivalent of `Place` located in `lbrustc_middle/mir`.
Separate PR for this move will make the actual PR for using Places to represent captures cleaner/more focused.
r? @nikomatsakis @matthewjasper
Teach bootstrap about target files vs target triples
`rustc` allows passing in predefined target triples as well as JSON
target specification files. This change allows bootstrap to have the
first inkling about those differences. This allows building a
cross-compiler for an out-of-tree architecture (even though that
compiler won't work for other reasons).
Even if no one ever uses this functionality, I think the newtype
around the `Interned<String>` improves the readability of the code.
Stop processing unreachable blocks when solving dataflow
...instead we `debug_assert` that the user is not checking the dataflow state for an unreachable block. This resolves a FIXME in the dataflow engine. The old behavior was an artifact of the previous dataflow framework. Things should run a tiny bit faster now, but I suspect not enough to show up in benchmarks. AFAIK, only the generator transform runs dataflow on MIR with unreachable basic blocks.
This PR also adds some utility methods to `mir::traversal`.
r? @pnkfelix
Add Arguments::as_str().
There exist quite a few macros in the Rust ecosystem which use `format_args!()` for formatting, but special case the one-argument case for optimization:
```rust
#[macro_export]
macro_rules! some_macro {
($s:expr) => { /* print &str directly, no formatting, no buffers */ };
($s:expr, $($tt:tt)*) => { /* use format_args to write to a buffer first */ }
}
```
E.g. [here](7a961f0fbe/src/macros.rs (L48-L58)), [here](20f9a9e223/src/macros.rs (L9-L17)), and [here](7b679cd6da/px4/src/logging.rs (L45-L52)).
The problem with these is that a forgotten argument such as in `some_macro!("{}")` will not be diagnosed, but just prints `"{}"`.
With this PR, it is possible to handle the no-arguments case separately *after* `format_args!()`, while simplifying the macro. Then these macros can give the proper error about a missing argument, just like `print!("{}")` does, while still using the same optimized implementation as before.
This is even more important with [RFC 2795](https://github.com/rust-lang/rfcs/pull/2795), to make sure `some_macro!("{some_variable}")` works as expected.
Fix MinGW `run-make-fulldeps` tests
`compiler-rt-works-on-mingw` and `libs-search-path` were not ran because `only-mingw` doesn't match any target.
Enabled and verified few ignored tests with `windows-gnu` toolchain. They are still ignored on MSVC since I'm not experienced with this target.
Make some Option methods const
Tracking issue: #67441
Constantify the following methods of `Option`:
- `as_ref`
- `is_some`
- `is_none`
- `iter` (not sure about this one, but it is possible, and will be useful when const traits are a thing)
cc @rust-lang/wg-const-eval @rust-lang/libs
Enforce even more the code blocks attributes check through rustdoc
`rustdoc` now has a lint which allows it to warn if a code block attribute is malformated (which can end up in bad situations, even more in case of testing examples!). Now it'll fail if such a situation is encountered when testing markdown code blocks examples.
r? @Mark-Simulacrum
This commit stops linting against `Box` in `extern "C" fn`s for the
`improper_ctypes_definitions` lint - boxes are documented to be
FFI-safe.
Signed-off-by: David Wood <david@davidtw.co>
When ran on Windows `cp` will follow symlink: `checkout/build/<target>/<stage>/lib/rustlib/src/rust`.
It points to `checkout` which means the test will get stuck in copying loop until there is no space left.
