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12f57721 MO |
1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* | |
3 | * Non-trivial C macros cannot be used in Rust. Similarly, inlined C functions | |
4 | * cannot be called either. This file explicitly creates functions ("helpers") | |
5 | * that wrap those so that they can be called from Rust. | |
6 | * | |
7 | * Even though Rust kernel modules should never use directly the bindings, some | |
8 | * of these helpers need to be exported because Rust generics and inlined | |
9 | * functions may not get their code generated in the crate where they are | |
10 | * defined. Other helpers, called from non-inline functions, may not be | |
11 | * exported, in principle. However, in general, the Rust compiler does not | |
12 | * guarantee codegen will be performed for a non-inline function either. | |
13 | * Therefore, this file exports all the helpers. In the future, this may be | |
14 | * revisited to reduce the number of exports after the compiler is informed | |
15 | * about the places codegen is required. | |
16 | * | |
17 | * All symbols are exported as GPL-only to guarantee no GPL-only feature is | |
18 | * accidentally exposed. | |
19 | */ | |
20 | ||
21 | #include <linux/bug.h> | |
22 | #include <linux/build_bug.h> | |
23 | ||
24 | __noreturn void rust_helper_BUG(void) | |
25 | { | |
26 | BUG(); | |
27 | } | |
28 | EXPORT_SYMBOL_GPL(rust_helper_BUG); | |
29 | ||
30 | /* | |
31 | * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type | |
32 | * as the Rust `usize` type, so we can use it in contexts where Rust | |
33 | * expects a `usize` like slice (array) indices. `usize` is defined to be | |
34 | * the same as C's `uintptr_t` type (can hold any pointer) but not | |
35 | * necessarily the same as `size_t` (can hold the size of any single | |
36 | * object). Most modern platforms use the same concrete integer type for | |
37 | * both of them, but in case we find ourselves on a platform where | |
38 | * that's not true, fail early instead of risking ABI or | |
39 | * integer-overflow issues. | |
40 | * | |
41 | * If your platform fails this assertion, it means that you are in | |
42 | * danger of integer-overflow bugs (even if you attempt to remove | |
43 | * `--size_t-is-usize`). It may be easiest to change the kernel ABI on | |
44 | * your platform such that `size_t` matches `uintptr_t` (i.e., to increase | |
45 | * `size_t`, because `uintptr_t` has to be at least as big as `size_t`). | |
46 | */ | |
47 | static_assert( | |
48 | sizeof(size_t) == sizeof(uintptr_t) && | |
49 | __alignof__(size_t) == __alignof__(uintptr_t), | |
50 | "Rust code expects C `size_t` to match Rust `usize`" | |
51 | ); |