October 2026 Monthly report

Overview

Thanks again to Open Source Security, inc and Embecosm for their ongoing support for this project.

Project update

The project merged 102 PRs merged in the last months, which is impressive considering the amount of travel that the team did to attend various conferences. We have made substantial progress on intrinsics, which are now complete minus a few volatile_* intrinsics that Zhi Heng is currently implementing. All of the missing intrinsics were added this months, which amounts to a total of 107 intrinsics implemented in the last few weeks. This affects our compilation of core as it relies on these intrinsics being present, but most importantly on them being accurate to the version that rustc emits. In some cases, it is not possible to reproduce the exact behavior of the intrinsic with GCC as opposed to LLVM, but these cases are exclusively for performance considerations - we have strived to make the underlying behavior of every intrinsic the exact same under gccrs.

For example, a intrinsics::nontemporal_store<T> is equivalent to a intrinsics::move_val_init<T> but with an extra marker to indicate to the backend that this data should not be held in cache. It is currently impossible to add this “marker” from a GCC frontend, so we simply emit the same code as a move_val_init when generating this intrinsic. Likewise, GCC’s __builtin_prefetch() does not allow prefetching from the instruction cache, as opposed to LLVM’s llvm.prefetch intrinsic. We thus… don’t prefetch instructions for prefetch_{write, read}_instruction<T>, which again only affects the performance of the produced binary, but not its behavior.

This month also saw a lot of work on external crate handling, with Pierre-Emmanuel making great progress on name resolving paths from external crates. We could not handle modules defined within external crates, and could not resolve global paths from other crates. Fixing this highlighted a slew of other issues and thus took a long time. We introduced a new testsuite focused on multi-crates testing to ensure we won’t introduce further regressions. We are also picking up the typechecking work and going through the last few remaining bugs with recursive types and slice intrinsics. These are the only few hurdles remaining before a full compilation of core.

On the side, we have also started experimenting with the BPF backend for GCC using gccrs. We are currently modifying the code from the SCX REEVDF scheduler (https://github.com/sched-ext/scx/) in order to get it to compile with gccrs. These projects are interesting, as they do not depend on the standard library, and are thus a perfect target for gccrs. We still need to tweak them a little as they are written in a more recent version of Rust than what gccrs is currently targeting, and thus make use of unsupported Rust language features such as if-let chains.

Our time in conferences during the last two months went extremely well, with a lot of interest in gccrs at RustConf, EuroRust, Kangrejos and Cauldron. We also gave a talk about the progress of the project at the Linux Plumbers Conference.

For now, only the recording of the RustConf talk is available: https://www.youtube.com/watch?v=GzxLOCigy60

We will be posting the other recordings as soon as we have them!

During the month of November, we plan on continuing the work on the typechecker and on the backend. We also want to start implementing CoercePointee properly, as it is an essential feature for the low-level alloc crate of the Linux kernel.

Call for contribution

• https://github.com/Rust-GCC/gccrs/issues/2500

• https://github.com/Rust-GCC/gccrs/issues/2376

Completed Activities

• intrinsics: Fix typecheck info for prefered_alignof<T> PR5035
• Add opening_{scoperesolution} flag to most resolution functions PR5030
• Sync with upstream (2026-10-27): bd2fde5d72893f4c1310b08a035b30ff0d8a4500 PR5028
• intrinsics: Add no-ops for prefetch_{read, writeinstruction} PR5025
• Emit extern prelude core path within builtin macros PR5023
• gccrs: Fix bitshift compound assignment type check PR5017
• Fix ICE with deep recursion in const fn PR5015
• intrinsics: Fix invalid error check after improvements to builtin lookup PR5011
• intrinsics: Add breakpoint and pref_alignof PR5008
• intrinsics: Add basic support for assert_uninitvalid<T> PR5007
• Sync with upstream (2026-10-21): bf99f4e35204f77c132dcb7fa958e590ace6306f PR5005
• intrinsics: Always warn on assert_zerovalid<T> PR5004
• intrinsics: Add exact_div PR5002
• gccrs: error when parsing only $ PR5000
• gccrs: Parse const blocks at the start of a statement PR4998
• Sync with upstream (2026-10-13): ca33fb40100211b9ed8c2e686b46cb9025791930 PR4995
• gccrs: check for curly/square braces in an attribute PR4994
• gccrs: Implement atomic binary operations, compare-exchange & min/max intrinsics PR4993
• Improve intrinsic interface PR4983
• gccrs: Fix ICE on rest patterns in enum tuple variants PR4979
• gccrs: Report non-exhaustive matches as E0004 PR4975
• gccrs: Fix ICE with nested patterns in multi-field constructors PR4974
• gccrs: Only add the requested auto trait when probing for a trait PR4972
• intrinsics: Add float_{tointunchecked} PR4970
• gccrs: Move derive_{coercepointee} to rfl features PR4969
• builtins: Improve lookup interface PR4968
• gccrs: Implement match arm guards PR4959
• gccrs: Evaluate call arguments from left to right PR4958
• gccrs: Add trait alias AST support PR4955
• gccrs: Resolve 2015 use paths from the crate root PR4954
• gccrs: Reject type param defaults using later params PR4953
• gccrs: Remove `extended<sub>keyvalueattributes</sub>` PR4952
• gccrs: Report an error when pub is not followed by an item PR4951
• Sync with upstream (2026-09-29): d9d90129f6dd53d2375c5a13a1563c4365e43a2f PR4946
• intrinsics: Add impl for fadd_fast, fsub_fast, fmul_fast, fdiv_fast and frem_fast PR4944
• backend: Properly implement remainder operation for f32 and f64 PR4943
• alloc: Test until typecheck PR4942
• gccrs: Handle 1.55 `rustc<sub>feature</sub>` PR4936
• gccrs: Add script to generate rustc-lib PR4934
• core: Test until typecheck PR4932
• gccrs: Correct the naming of atomic store & load intrinsics PR4931
• gccrs: Diagnose unsigned arithmetic overflow in constant evaluation PR4930
• gccrs: Handle FUNCTION segments in new_typeparam PR4929
• gccrs: Improve bodyless function pattern check PR4928
• gccrs: Ignore bindings on bodyless functions PR4927
• gccrs: Remove -frust-c-style-string-literals flag PR4925
• gccrs: Initial implementation of hotpatching rustc-lib PR4924
• gccrs: fix unconstrained check to look for constrained bindings PR4923
• gccrs: Add missing lifetime handling to trait resolve PR4922
• gccrs: Add type bound predicate scan PR4921
• gccrs: Add flag to unify of expect never PR4919
• parse: Remove unused gating_errors field and accessor PR4910
• gccrs: add ParamType::clone recusion guard PR4909
• gccrs: Fix bad substituion error PR4908
• gccrs: Add testcase to show issue fixed PR4907
• gccrs: Add testcase to show issue is fixed PR4906
• gccrs: Recursive types support PR4905
• gccrs: Fix unconstrained when args are in the where clause PR4903
• nr2.0: Close out invalid resolution for unexported items PR4902
• gccrs: nr1.0: Remove old `Scope` class PR4901
• gccrs: handle lifetimes properly on trait items PR4900
• gccrs: Fix ICE in constexpr for unit-structs PR4899
• gccrs: Add test-case to show ice fixed PR4898
• gccrs: Add testcase to show issue fixed PR4897
• gccrs: Remove unnessecary diagnostics on array capacity values PR4896
• gccrs: add null guard for failed builtin expansion PR4895
• Sync with upstream (2026-09-14): 4442e8b6cbffd113ec7bd25f449cc18f104f7150 PR4893
• gccrs: Support silly legacy rustc const generics for stdarch PR4892
• gccrs: Implement some platform-intrinsic simd function support PR4891
• Move issue related tests to their own directory PR4890
• gccrs: This is an utterly insane rustc shim needed for stdarch PR4889
• gccrs: remove unused callback substitution system PR4888
• gccrs: Change alloc crate test edition to 2018 PR4887
• gccrs: Fix `HIR::ClosureExpr` copying PR4886
• gccrs: Only the last segment should resolve to an expr item PR4882
• gccrs: Refactor query_type to only fully-const resolve const fns PR4881
• gccrs: Fix bad derive of Ord to use Self instead of raw type-name PR4880
• Clean up hir map PR4878
• gccrs: constructors that get borrowed need to be addressable PR4877
• gccrs: Fix handling where clauses into two passes PR4875
• gccrs: filter out candidates by checking if self is compatable PR4874
• gccrs: walk the binding generic arguments for unconstrained checks PR4873
• gccrs: Track lifetimes per trait item PR4872
• gccrs: Add missing isize and usize as valid options here PR4871
• gccrs: Stop method selection when we hit generic params PR4870
• gccrs: Fix return type leaking into other function contexts PR4869
• gccrs: use std::move to reduce copy ctor usage on type-bound-predicate PR4857
• gccrs: Fix bug when compiling const position intrinsic calls PR4856
• gccrs: Handle generic args to traits in paths PR4854
• gccrs: Fix handling of constants in paths PR4852
• gccrs: improve handling of defered operator overload handling PR4850
• gccrs: Remove rust_unreachable from grs_{langhookpushdecl} PR4848
• Improve method resolution by using indexes PR4847
• Recognize the `#[cfi<sub>encoding</sub>]` attribute and warn that it does nothing PR4846
• gccrs: Remove bad unify in operator overload breaking partial eq in core PR4845
• Fix ICE 4735 PR4844
• gccrs: Fix parser handling for Foo<Bar: SomeTrait> PR4843
• Add base feature gating for `derive(CoercePointee)` PR4841
• gccrs: Add new resolution mode CANONICAL/REFERNECE to type-check-type PR4840
• attr: Allow `#[used]` attribute and its argument variant. PR4837
• codegen: Compile extern types as C void PR4834
• Extern prelude handling PR4758

Contributors this month

• Wesley Lewis (new contributor!)
• Philip Herron
• Zhi Heng
• Marc Poulhiès
• Enes Cevik
• Owen Avery
• Utkarsh Bahuguna
• Pierre-Emmanuel Patry
• Arthur Cohen

Overall Task Status

Bugs

Test Cases

Milestones Progress

Here is the list of overarching milestones gccrs is currently targeting. We’ll use the acronym in the following milestone tables, in the column named “OA Milest.”.