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This is the next upgrade to the Rust toolchain, from 1.77.1 to 1.78.0
(i.e. the latest) [1].
See the upgrade policy [2] and the comments on the first upgrade in
commit 3ed03f4da0 ("rust: upgrade to Rust 1.68.2").
It is much smaller than previous upgrades, since the `alloc` fork was
dropped in commit 9d0441bab7 ("rust: alloc: remove our fork of the
`alloc` crate") [3].
# Unstable features
There have been no changes to the set of unstable features used in
our own code. Therefore, the only unstable features allowed to be used
outside the `kernel` crate is still `new_uninit`.
However, since we finally dropped our `alloc` fork [3], all the unstable
features used by `alloc` (~30 language ones, ~60 library ones) are not
a concern anymore. This reduces the maintenance burden, increases the
chances of new compiler versions working without changes and gets us
closer to the goal of supporting several compiler versions.
It also means that, ignoring non-language/library features, we are
currently left with just the few language features needed to implement the
kernel `Arc`, the `new_uninit` library feature, the `compiler_builtins`
marker and the few `no_*` `cfg`s we pass when compiling `core`/`alloc`.
Please see [4] for details.
# Required changes
## LLVM's data layout
Rust 1.77.0 (i.e. the previous upgrade) introduced a check for matching
LLVM data layouts [5]. Then, Rust 1.78.0 upgraded LLVM's bundled major
version from 17 to 18 [6], which changed the data layout in x86 [7]. Thus
update the data layout in our custom target specification for x86 so
that the compiler does not complain about the mismatch:
error: data-layout for target `target-5559158138856098584`,
`e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128`,
differs from LLVM target's `x86_64-linux-gnu` default layout,
`e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128`
In the future, the goal is to drop the custom target specifications.
Meanwhile, if we want to support other LLVM versions used in `rustc`
(e.g. for LTO), we will need to add some extra logic (e.g. conditional on
LLVM's version, or extracting the data layout from an existing built-in
target specification).
## `unused_imports`
Rust's `unused_imports` lint covers both unused and redundant imports.
Now, in 1.78.0, the lint detects more cases of redundant imports [8].
Thus one of the previous patches cleaned them up.
## Clippy's `new_without_default`
Clippy now suggests to implement `Default` even when `new()` is `const`,
since `Default::default()` may call `const` functions even if it is not
`const` itself [9]. Thus one of the previous patches implemented it.
# Other changes in Rust
Rust 1.78.0 introduced `feature(asm_goto)` [10] [11]. This feature was
discussed in the past [12].
Rust 1.78.0 introduced `feature(const_refs_to_static)` [13] to allow
referencing statics in constants and extended `feature(const_mut_refs)`
to allow raw mutable pointers in constants. Together, this should cover
the kernel's `VTABLE` use case. In fact, the implementation [14] in
upstream Rust added a test case for it [15].
Rust 1.78.0 with debug assertions enabled (i.e. `-Cdebug-assertions=y`,
kernel's `CONFIG_RUST_DEBUG_ASSERTIONS=y`) now always checks all unsafe
preconditions, though without a way to opt-out for particular cases [16].
It would be ideal to have a way to selectively disable certain checks
per-call site for this one (i.e. not just per check but for particular
instances of a check), even if the vast majority of the checks remain
in place [17].
Rust 1.78.0 also improved a couple issues we reported when giving feedback
for the new `--check-cfg` feature [18] [19].
# `alloc` upgrade and reviewing
As mentioned above, compiler upgrades will not update `alloc` anymore,
since we dropped our `alloc` fork [3].
Link: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1780-2024-05-02 [1]
Link: https://rust-for-linux.com/rust-version-policy [2]
Link: https://lore.kernel.org/rust-for-linux/20240328013603.206764-1-wedsonaf@gmail.com/ [3]
Link: https://github.com/Rust-for-Linux/linux/issues/2 [4]
Link: https://github.com/rust-lang/rust/pull/120062 [5]
Link: https://github.com/rust-lang/rust/pull/120055 [6]
Link: https://reviews.llvm.org/D86310 [7]
Link: https://github.com/rust-lang/rust/pull/117772 [8]
Link: https://github.com/rust-lang/rust-clippy/pull/10903 [9]
Link: https://github.com/rust-lang/rust/pull/119365 [10]
Link: https://github.com/rust-lang/rust/issues/119364 [11]
Link: https://lore.kernel.org/rust-for-linux/ZWipTZysC2YL7qsq@Boquns-Mac-mini.home/ [12]
Link: https://github.com/rust-lang/rust/issues/119618 [13]
Link: https://github.com/rust-lang/rust/pull/120932 [14]
Link: https://github.com/rust-lang/rust/pull/120932/files#diff-e6fc1622c46054cd46b1d225c5386c5554564b3b0fa8a03c2dc2d8627a1079d9 [15]
Link: https://github.com/rust-lang/rust/issues/120969 [16]
Link: https://github.com/Rust-for-Linux/linux/issues/354 [17]
Link: https://github.com/rust-lang/rust/pull/121202 [18]
Link: https://github.com/rust-lang/rust/pull/121237 [19]
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20240401212303.537355-4-ojeda@kernel.org
[ Added a few more details and links I mentioned in the list. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Pull arm64 updates from Catalin Marinas:
"The major features are support for LPA2 (52-bit VA/PA with 4K and 16K
pages), the dpISA extension and Rust enabled on arm64. The changes are
mostly contained within the usual arch/arm64/, drivers/perf, the arm64
Documentation and kselftests. The exception is the Rust support which
touches some generic build files.
Summary:
- Reorganise the arm64 kernel VA space and add support for LPA2 (at
stage 1, KVM stage 2 was merged earlier) - 52-bit VA/PA address
range with 4KB and 16KB pages
- Enable Rust on arm64
- Support for the 2023 dpISA extensions (data processing ISA), host
only
- arm64 perf updates:
- StarFive's StarLink (integrates one or more CPU cores with a
shared L3 memory system) PMU support
- Enable HiSilicon Erratum 162700402 quirk for HIP09
- Several updates for the HiSilicon PCIe PMU driver
- Arm CoreSight PMU support
- Convert all drivers under drivers/perf/ to use .remove_new()
- Miscellaneous:
- Don't enable workarounds for "rare" errata by default
- Clean up the DAIF flags handling for EL0 returns (in preparation
for NMI support)
- Kselftest update for ptrace()
- Update some of the sysreg field definitions
- Slight improvement in the code generation for inline asm I/O
accessors to permit offset addressing
- kretprobes: acquire regs via a BRK exception (previously done
via a trampoline handler)
- SVE/SME cleanups, comment updates
- Allow CALL_OPS+CC_OPTIMIZE_FOR_SIZE with clang (previously
disabled due to gcc silently ignoring -falign-functions=N)"
* tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (134 commits)
Revert "mm: add arch hook to validate mmap() prot flags"
Revert "arm64: mm: add support for WXN memory translation attribute"
Revert "ARM64: Dynamically allocate cpumasks and increase supported CPUs to 512"
ARM64: Dynamically allocate cpumasks and increase supported CPUs to 512
kselftest/arm64: Add 2023 DPISA hwcap test coverage
kselftest/arm64: Add basic FPMR test
kselftest/arm64: Handle FPMR context in generic signal frame parser
arm64/hwcap: Define hwcaps for 2023 DPISA features
arm64/ptrace: Expose FPMR via ptrace
arm64/signal: Add FPMR signal handling
arm64/fpsimd: Support FEAT_FPMR
arm64/fpsimd: Enable host kernel access to FPMR
arm64/cpufeature: Hook new identification registers up to cpufeature
docs: perf: Fix build warning of hisi-pcie-pmu.rst
perf: starfive: Only allow COMPILE_TEST for 64-bit architectures
MAINTAINERS: Add entry for StarFive StarLink PMU
docs: perf: Add description for StarFive's StarLink PMU
dt-bindings: perf: starfive: Add JH8100 StarLink PMU
perf: starfive: Add StarLink PMU support
docs: perf: Update usage for target filter of hisi-pcie-pmu
...
This script takes care of generating the custom target specification
file for `rustc`, based on the kernel configuration.
It also serves as an example of a Rust host program.
A dummy architecture is kept in this patch so that a later patch
adds x86 support on top with as few changes as possible.
Reviewed-by: Kees Cook <keescook@chromium.org>
Co-developed-by: Alex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: Alex Gaynor <alex.gaynor@gmail.com>
Co-developed-by: Wedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: Wedson Almeida Filho <wedsonaf@google.com>
Co-developed-by: David Gow <davidgow@google.com>
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
