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![Miguel Ojeda](/assets/img/avatar_default.png)
This is the second upgrade to the Rust toolchain, from 1.68.2 to 1.71.1
(i.e. the latest).
See the upgrade policy [1] and the comments on the first upgrade in
commit 3ed03f4da0
("rust: upgrade to Rust 1.68.2").
# Unstable features
No unstable features (that we use) were stabilized.
Therefore, the only unstable feature allowed to be used outside
the `kernel` crate is still `new_uninit`, though other code to be
upstreamed may increase the list.
Please see [2] for details.
# Required changes
For the upgrade, this patch requires the following changes:
- Removal of the `__rust_*` allocator functions, together with
the addition of the `__rust_no_alloc_shim_is_unstable` static.
See [3] for details.
- Some more compiler builtins added due to `<f{32,64}>::midpoint()`
that got added in Rust 1.71 [4].
# `alloc` upgrade and reviewing
The vast majority of changes are due to our `alloc` fork being upgraded
at once.
There are two kinds of changes to be aware of: the ones coming from
upstream, which we should follow as closely as possible, and the updates
needed in our added fallible APIs to keep them matching the newer
infallible APIs coming from upstream.
Instead of taking a look at the diff of this patch, an alternative
approach is reviewing a diff of the changes between upstream `alloc` and
the kernel's. This allows to easily inspect the kernel additions only,
especially to check if the fallible methods we already have still match
the infallible ones in the new version coming from upstream.
Another approach is reviewing the changes introduced in the additions in
the kernel fork between the two versions. This is useful to spot
potentially unintended changes to our additions.
To apply these approaches, one may follow steps similar to the following
to generate a pair of patches that show the differences between upstream
Rust and the kernel (for the subset of `alloc` we use) before and after
applying this patch:
# Get the difference with respect to the old version.
git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
cut -d/ -f3- |
grep -Fv README.md |
xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
git -C linux diff --patch-with-stat --summary -R > old.patch
git -C linux restore rust/alloc
# Apply this patch.
git -C linux am rust-upgrade.patch
# Get the difference with respect to the new version.
git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
cut -d/ -f3- |
grep -Fv README.md |
xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
git -C linux diff --patch-with-stat --summary -R > new.patch
git -C linux restore rust/alloc
Now one may check the `new.patch` to take a look at the additions (first
approach) or at the difference between those two patches (second
approach). For the latter, a side-by-side tool is recommended.
Link: https://rust-for-linux.com/rust-version-policy [1]
Link: https://github.com/Rust-for-Linux/linux/issues/2 [2]
Link: https://github.com/rust-lang/rust/pull/86844 [3]
Link: https://github.com/rust-lang/rust/pull/92048 [4]
Closes: https://github.com/Rust-for-Linux/linux/issues/68
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Trevor Gross <tmgross@umich.edu>
Link: https://lore.kernel.org/r/20230729220317.416771-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
88 lines
3.4 KiB
Rust
88 lines
3.4 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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//! Allocator support.
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use core::alloc::{GlobalAlloc, Layout};
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use core::ptr;
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use crate::bindings;
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struct KernelAllocator;
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/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
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///
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/// # Safety
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///
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/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
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/// - `new_layout` must have a non-zero size.
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unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: bindings::gfp_t) -> *mut u8 {
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// Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
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let layout = new_layout.pad_to_align();
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let mut size = layout.size();
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if layout.align() > bindings::BINDINGS_ARCH_SLAB_MINALIGN {
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// The alignment requirement exceeds the slab guarantee, thus try to enlarge the size
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// to use the "power-of-two" size/alignment guarantee (see comments in `kmalloc()` for
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// more information).
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//
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// Note that `layout.size()` (after padding) is guaranteed to be a multiple of
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// `layout.align()`, so `next_power_of_two` gives enough alignment guarantee.
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size = size.next_power_of_two();
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}
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// SAFETY:
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// - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
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// function safety requirement.
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// - `size` is greater than 0 since it's either a `layout.size()` (which cannot be zero
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// according to the function safety requirement) or a result from `next_power_of_two()`.
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unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags) as *mut u8 }
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}
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unsafe impl GlobalAlloc for KernelAllocator {
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unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
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// SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
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// requirement.
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unsafe { krealloc_aligned(ptr::null_mut(), layout, bindings::GFP_KERNEL) }
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}
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unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
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unsafe {
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bindings::kfree(ptr as *const core::ffi::c_void);
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}
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}
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unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
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// SAFETY:
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// - `new_size`, when rounded up to the nearest multiple of `layout.align()`, will not
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// overflow `isize` by the function safety requirement.
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// - `layout.align()` is a proper alignment (i.e. not zero and must be a power of two).
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let layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
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// SAFETY:
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// - `ptr` is either null or a pointer allocated by this allocator by the function safety
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// requirement.
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// - the size of `layout` is not zero because `new_size` is not zero by the function safety
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// requirement.
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unsafe { krealloc_aligned(ptr, layout, bindings::GFP_KERNEL) }
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}
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unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
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// SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
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// requirement.
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unsafe {
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krealloc_aligned(
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ptr::null_mut(),
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layout,
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bindings::GFP_KERNEL | bindings::__GFP_ZERO,
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)
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}
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}
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}
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#[global_allocator]
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static ALLOCATOR: KernelAllocator = KernelAllocator;
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// See <https://github.com/rust-lang/rust/pull/86844>.
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#[no_mangle]
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static __rust_no_alloc_shim_is_unstable: u8 = 0;
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