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| -rw-r--r-- | rust/helpers.c | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/rust/helpers.c b/rust/helpers.c new file mode 100644 index 000000000000..b4f15eee2ffd --- /dev/null +++ b/rust/helpers.c @@ -0,0 +1,51 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Non-trivial C macros cannot be used in Rust. Similarly, inlined C functions + * cannot be called either. This file explicitly creates functions ("helpers") + * that wrap those so that they can be called from Rust. + * + * Even though Rust kernel modules should never use directly the bindings, some + * of these helpers need to be exported because Rust generics and inlined + * functions may not get their code generated in the crate where they are + * defined. Other helpers, called from non-inline functions, may not be + * exported, in principle. However, in general, the Rust compiler does not + * guarantee codegen will be performed for a non-inline function either. + * Therefore, this file exports all the helpers. In the future, this may be + * revisited to reduce the number of exports after the compiler is informed + * about the places codegen is required. + * + * All symbols are exported as GPL-only to guarantee no GPL-only feature is + * accidentally exposed. + */ + +#include <linux/bug.h> +#include <linux/build_bug.h> + +__noreturn void rust_helper_BUG(void) +{ + BUG(); +} +EXPORT_SYMBOL_GPL(rust_helper_BUG); + +/* + * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type + * as the Rust `usize` type, so we can use it in contexts where Rust + * expects a `usize` like slice (array) indices. `usize` is defined to be + * the same as C's `uintptr_t` type (can hold any pointer) but not + * necessarily the same as `size_t` (can hold the size of any single + * object). Most modern platforms use the same concrete integer type for + * both of them, but in case we find ourselves on a platform where + * that's not true, fail early instead of risking ABI or + * integer-overflow issues. + * + * If your platform fails this assertion, it means that you are in + * danger of integer-overflow bugs (even if you attempt to remove + * `--size_t-is-usize`). It may be easiest to change the kernel ABI on + * your platform such that `size_t` matches `uintptr_t` (i.e., to increase + * `size_t`, because `uintptr_t` has to be at least as big as `size_t`). + */ +static_assert( + sizeof(size_t) == sizeof(uintptr_t) && + __alignof__(size_t) == __alignof__(uintptr_t), + "Rust code expects C `size_t` to match Rust `usize`" +); |