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
rust_helper_BUG(void)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 );
52
