forked from mirrors/linux
9dc0436550
This is a basic implementation of `Arc` backed by C's `refcount_t`. It allows Rust code to idiomatically allocate memory that is ref-counted. Cc: Will Deacon <will@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com> Reviewed-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Gary Guo <gary@garyguo.net> Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com> Acked-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
70 lines
2.6 KiB
C
70 lines
2.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Non-trivial C macros cannot be used in Rust. Similarly, inlined C functions
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* cannot be called either. This file explicitly creates functions ("helpers")
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* that wrap those so that they can be called from Rust.
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*
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* Even though Rust kernel modules should never use directly the bindings, some
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* of these helpers need to be exported because Rust generics and inlined
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* functions may not get their code generated in the crate where they are
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* defined. Other helpers, called from non-inline functions, may not be
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* exported, in principle. However, in general, the Rust compiler does not
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* guarantee codegen will be performed for a non-inline function either.
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* Therefore, this file exports all the helpers. In the future, this may be
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* revisited to reduce the number of exports after the compiler is informed
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* about the places codegen is required.
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*
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* All symbols are exported as GPL-only to guarantee no GPL-only feature is
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* accidentally exposed.
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*/
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#include <linux/bug.h>
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#include <linux/build_bug.h>
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#include <linux/refcount.h>
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__noreturn void rust_helper_BUG(void)
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{
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BUG();
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}
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EXPORT_SYMBOL_GPL(rust_helper_BUG);
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refcount_t rust_helper_REFCOUNT_INIT(int n)
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{
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return (refcount_t)REFCOUNT_INIT(n);
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}
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EXPORT_SYMBOL_GPL(rust_helper_REFCOUNT_INIT);
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void rust_helper_refcount_inc(refcount_t *r)
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{
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refcount_inc(r);
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}
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EXPORT_SYMBOL_GPL(rust_helper_refcount_inc);
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bool rust_helper_refcount_dec_and_test(refcount_t *r)
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{
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return refcount_dec_and_test(r);
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}
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EXPORT_SYMBOL_GPL(rust_helper_refcount_dec_and_test);
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/*
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* We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
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* as the Rust `usize` type, so we can use it in contexts where Rust
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* expects a `usize` like slice (array) indices. `usize` is defined to be
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* the same as C's `uintptr_t` type (can hold any pointer) but not
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* necessarily the same as `size_t` (can hold the size of any single
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* object). Most modern platforms use the same concrete integer type for
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* both of them, but in case we find ourselves on a platform where
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* that's not true, fail early instead of risking ABI or
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* integer-overflow issues.
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*
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* If your platform fails this assertion, it means that you are in
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* danger of integer-overflow bugs (even if you attempt to remove
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* `--size_t-is-usize`). It may be easiest to change the kernel ABI on
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* your platform such that `size_t` matches `uintptr_t` (i.e., to increase
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* `size_t`, because `uintptr_t` has to be at least as big as `size_t`).
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*/
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static_assert(
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sizeof(size_t) == sizeof(uintptr_t) &&
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__alignof__(size_t) == __alignof__(uintptr_t),
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"Rust code expects C `size_t` to match Rust `usize`"
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);
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