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On the 32-bit win7 target, we use OS TLS instead of native TLS, due to
issues with how the OS handles alignment. Unfortunately, this caused
issues due to the TLS destructors not running, causing memory leaks
among other problems.
On Windows, to support OS TLS, the TlsAlloc family of function is used
by Rust. This function does not support TLS destructors at all. However,
rust has some code to emulate those destructors, by leveraging the TLS
support functionality found in the MSVC CRT (specifically, in tlssup.c
of the CRT). Specifically, the CRT provides the ability to register
callbacks that are called (among other things) on thread destruction. By
registering our own callback, we can run through a list of registered
destructors functions to execute.
To use this functionality, the user must do two things:
1. They must put the address to their callback in a section between
`.CRT$XLB` and `.CRT$XLY`.
2. They must add a reference to `_tls_used` (or `__tls_used` on x86) to
make sure the TLS support code in tlssup.c isn't garbage collected by
the linker.
Prior to this commit, this second bit wasn't being done properly by the
Rust TLS support code. Instead of adding a reference to _tls_used, it
instead had a reference to its own callback to prevent it from getting
GC'd by the linker. While this is _also_ necessary, not having a
reference on _tls_used made the entire support non-functional.
This commit reworks the code to:
1. Add an unconditional `#[used]` attribute on the CALLBACK, which
should be enough to prevent it from getting GC'd by the linker.
2. Add a reference to `_tls_used`, which should pull the TLS support
code into the Rust programs and not let it be GC'd by the linker.
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std: abort the process on failure to allocate a TLS key
The panic machinery uses TLS, so panicking if no TLS keys are left can lead to infinite recursion (see https://github.com/rust-lang/rust/issues/140798#issuecomment-2872307377). Rather than having separate logic for the panic count and the thread name, just always abort the process if a TLS key allocation fails. This also has the benefit of aligning the key-based TLS implementation with the documentation, which does not mention that a panic could also occur because of resource exhaustion.
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The panic machinery uses TLS, so panicking if no TLS keys are left can lead to infinite recursion (see https://github.com/rust-lang/rust/issues/140798#issuecomment-2872307377). Rather than having separate logic for the panic count and the thread name, just always abort the process if a TLS key allocation fails. This also has the benefit of aligning the key-based TLS implementation with the documentation, which does not mention that a panic could also occur because of resource exhaustion.
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in core/alloc/std only for now, and ignoring test files
Co-authored-by: Pavel Grigorenko <GrigorenkoPV@ya.ru>
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Previously (https://github.com/rust-lang/rust/pull/115200,
https://github.com/rust-lang/rust/pull/138002), we
added `#[no_sanitize(cfi)]` to all code paths that call to a weakly
linked function.
In https://github.com/rust-lang/rust/pull/138349 we fixed the root cause
for this issue, which means we can now remove the corresponding
attributes.
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Rename internal module from `statik` to `no_threads`
This module is named in reference to the keyword, but the term is somewhat overloaded. Rename it to more clearly describe it and avoid the misspelling.
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This module is named in reference to the keyword, but the term is
somewhat overloaded. Rename it to more clearly describe it and avoid the
misspelling.
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Use `std::mem::{size_of, size_of_val, align_of, align_of_val}` from the
prelude instead of importing or qualifying them.
These functions were added to all preludes in Rust 1.80.
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#109797 is fixed
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Run TLS destructors for wasm32-wasip1-threads
The target wasm32-wasip1-threads has support for pthreads and allows registration of TLS destructors.
For spawned threads, this registers Rust TLS destructors by creating a pthreads key with an attached destructor function.
For the main thread, this registers an `atexit` handler to run the TLS destructors.
try-job: test-various
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The target has support for pthreads and allows
registration of TLS destructors.
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Since `#[link_section]` is enclosed in braces, it was being confused with a link during docs compilation.
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Fundamentally, we have *three* disjoint categories of functions:
1. const-stable functions
2. private/unstable functions that are meant to be callable from const-stable functions
3. functions that can make use of unstable const features
This PR implements the following system:
- `#[rustc_const_stable]` puts functions in the first category. It may only be applied to `#[stable]` functions.
- `#[rustc_const_unstable]` by default puts functions in the third category. The new attribute `#[rustc_const_stable_indirect]` can be added to such a function to move it into the second category.
- `const fn` without a const stability marker are in the second category if they are still unstable. They automatically inherit the feature gate for regular calls, it can now also be used for const-calls.
Also, several holes in recursive const stability checking are being closed.
There's still one potential hole that is hard to avoid, which is when MIR
building automatically inserts calls to a particular function in stable
functions -- which happens in the panic machinery. Those need to *not* be
`rustc_const_unstable` (or manually get a `rustc_const_stable_indirect`) to be
sure they follow recursive const stability. But that's a fairly rare and special
case so IMO it's fine.
The net effect of this is that a `#[unstable]` or unmarked function can be
constified simply by marking it as `const fn`, and it will then be
const-callable from stable `const fn` and subject to recursive const stability
requirements. If it is publicly reachable (which implies it cannot be unmarked),
it will be const-unstable under the same feature gate. Only if the function ever
becomes `#[stable]` does it need a `#[rustc_const_unstable]` or
`#[rustc_const_stable]` marker to decide if this should also imply
const-stability.
Adding `#[rustc_const_unstable]` is only needed for (a) functions that need to
use unstable const lang features (including intrinsics), or (b) `#[stable]`
functions that are not yet intended to be const-stable. Adding
`#[rustc_const_stable]` is only needed for functions that are actually meant to
be directly callable from stable const code. `#[rustc_const_stable_indirect]` is
used to mark intrinsics as const-callable and for `#[rustc_const_unstable]`
functions that are actually called from other, exposed-on-stable `const fn`. No
other attributes are required.
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Fixes #131863 for wasm targets
All other macros were done in #131866, but this sub module is missed.
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By using qualified imports, i.e. `$crate::...::LocalKey`.
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Since the stabilization in #127679 has reached stage0, 1.82-beta, we can
start using `&raw` freely, and even the soft-deprecated `ptr::addr_of!`
and `ptr::addr_of_mut!` can stop allowing the unstable feature.
I intentionally did not change any documentation or tests, but the rest
of those macro uses are all now using `&raw const` or `&raw mut` in the
standard library.
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The previous commit updated `rustfmt.toml` appropriately. This commit is
the outcome of running `x fmt --all` with the new formatting options.
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Many tiny changes to stdlib doc comments to make them consistent (for example
"Returns foo", rather than "Return foo", per RFC1574), adding missing periods, paragraph
breaks, backticks for monospace style, and other minor nits.
https://github.com/rust-lang/rfcs/blob/master/text/1574-more-api-documentation-conventions.md#appendix-a-full-conventions-text
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Currently, `std` performs an atomic load to get the OS key on every access to `StaticKey` even when the key is already known. This PR thus replaces `StaticKey` with the platform-specific `get` and `set` function and a new `LazyKey` type that acts as a `LazyLock<Key>`, allowing the reuse of the retreived key for multiple accesses.
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As discovered by Mara in #110897, our TLS implementation is a total mess. In the past months, I have simplified the actual macros and their expansions, but the majority of the complexity comes from the platform-specific support code needed to create keys and register destructors. In keeping with #117276, I have therefore moved all of the `thread_local_key`/`thread_local_dtor` modules to the `thread_local` module in `sys` and merged them into a new structure, so that future porters of `std` can simply mix-and-match the existing code instead of having to copy the same (bad) implementation everywhere. The new structure should become obvious when looking at `sys/thread_local/mod.rs`.
Unfortunately, the documentation changes associated with the refactoring have made this PR rather large. That said, this contains no functional changes except for two small ones:
* the key-based destructor fallback now, by virtue of sharing the implementation used by macOS and others, stores its list in a `#[thread_local]` static instead of in the key, eliminating one indirection layer and drastically simplifying its code.
* I've switched over ZKVM (tier 3) to use the same implementation as WebAssembly, as the implementation was just a way worse version of that
Please let me know if I can make this easier to review! I know these large PRs aren't optimal, but I couldn't think of any good intermediate steps.
@rustbot label +A-thread-locals
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Make TLS accessors closures that return pointers
The current TLS macros generate a function that returns an `Option<&'static T>`. This is both risky as we lie about lifetimes, and necessitates that those functions are `unsafe`. By returning a `*const T` instead, the accessor function do not have safety requirements any longer and can be made closures without hassle. This PR does exactly that!
For native TLS, the closure approach makes it trivial to select the right accessor function at compile-time, which could result in a slight speed-up (I have the hope that the accessors are now simple enough for the MIR-inliner to kick in).
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