Re: [PATCH v2 5/5] panic_qr: use new #[export] macro

Simona Vetter
2025-02-28T17:06:39Z

On Fri, Feb 28, 2025 at 12:39:34PM +0000, Alice Ryhl wrote:
> This validates at compile time that the signatures match what is in the
> header file. It highlights one annoyance with the compile-time check,
> which is that it can only be used with functions marked unsafe.
>
> If the function is not unsafe, then this error is emitted:
>
> error[E0308]: `if` and `else` have incompatible types
> --> <linux>/drivers/gpu/drm/drm_panic_qr.rs:987:19
> |
> 986 | #[export]
> | --------- expected because of this
> 987 | pub extern "C" fn drm_panic_qr_max_data_size(version: u8, url_len: usize) -> usize {
> | ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected unsafe fn, found safe fn
> |
> = note: expected fn item `unsafe extern "C" fn(_, _) -> _ {kernel::bindings::drm_panic_qr_max_data_size}`
> found fn item `extern "C" fn(_, _) -> _ {drm_panic_qr_max_data_size}`
>
> Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>

I guess makes most sense to land this all through a rust tree, for that:

Acked-by: Simona Vetter <simona.vetter@ffwll.ch>

The rust macro magic definitely flies above my head, so no revivew from
me.

Cheers, Sima

> ---
> drivers/gpu/drm/drm_panic.c | 5 -----
> drivers/gpu/drm/drm_panic_qr.rs | 15 +++++++++++----
> include/drm/drm_panic.h | 7 +++++++
> rust/bindings/bindings_helper.h | 4 ++++
> 4 files changed, 22 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
> index f128d345b16d..dee5301dd729 100644
> --- a/drivers/gpu/drm/drm_panic.c
> +++ b/drivers/gpu/drm/drm_panic.c
> @@ -486,11 +486,6 @@ static void drm_panic_qr_exit(void)
> stream.workspace = NULL;
> }
>
> -extern size_t drm_panic_qr_max_data_size(u8 version, size_t url_len);
> -
> -extern u8 drm_panic_qr_generate(const char *url, u8 *data, size_t data_len, size_t data_size,
> - u8 *tmp, size_t tmp_size);
> -
> static int drm_panic_get_qr_code_url(u8 **qr_image)
> {
> struct kmsg_dump_iter iter;
> diff --git a/drivers/gpu/drm/drm_panic_qr.rs b/drivers/gpu/drm/drm_panic_qr.rs
> index bcf248f69252..d055655aa0cd 100644
> --- a/drivers/gpu/drm/drm_panic_qr.rs
> +++ b/drivers/gpu/drm/drm_panic_qr.rs
> @@ -27,7 +27,10 @@
> //! * <https://github.com/bjguillot/qr>
>
> use core::cmp;
> -use kernel::str::CStr;
> +use kernel::{
> + prelude::*,
> + str::CStr,
> +};
>
> #[derive(Debug, Clone, Copy, PartialEq, Eq, Ord, PartialOrd)]
> struct Version(usize);
> @@ -929,7 +932,7 @@ fn draw_all(&mut self, data: impl Iterator<Item = u8>) {
> /// * `tmp` must be valid for reading and writing for `tmp_size` bytes.
> ///
> /// They must remain valid for the duration of the function call.
> -#[no_mangle]
> +#[export]
> pub unsafe extern "C" fn drm_panic_qr_generate(
> url: *const kernel::ffi::c_char,
> data: *mut u8,
> @@ -980,8 +983,12 @@ fn draw_all(&mut self, data: impl Iterator<Item = u8>) {
> /// * If `url_len` > 0, remove the 2 segments header/length and also count the
> /// conversion to numeric segments.
> /// * If `url_len` = 0, only removes 3 bytes for 1 binary segment.
> -#[no_mangle]
> -pub extern "C" fn drm_panic_qr_max_data_size(version: u8, url_len: usize) -> usize {
> +///
> +/// # Safety
> +///
> +/// Always safe to call.
> +#[export]
> +pub unsafe extern "C" fn drm_panic_qr_max_data_size(version: u8, url_len: usize) -> usize {
> #[expect(clippy::manual_range_contains)]
> if version < 1 || version > 40 {
> return 0;
> diff --git a/include/drm/drm_panic.h b/include/drm/drm_panic.h
> index f4e1fa9ae607..2a1536e0229a 100644
> --- a/include/drm/drm_panic.h
> +++ b/include/drm/drm_panic.h
> @@ -163,4 +163,11 @@ static inline void drm_panic_unlock(struct drm_device *dev, unsigned long flags)
>
> #endif
>
> +#if defined(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
> +extern size_t drm_panic_qr_max_data_size(u8 version, size_t url_len);
> +
> +extern u8 drm_panic_qr_generate(const char *url, u8 *data, size_t data_len, size_t data_size,
> + u8 *tmp, size_t tmp_size);
> +#endif
> +
> #endif /* __DRM_PANIC_H__ */
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 55354e4dec14..5345aa93fb8a 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -36,6 +36,10 @@
> #include <linux/workqueue.h>
> #include <trace/events/rust_sample.h>
>
> +#if defined(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
> +#include <drm/drm_panic.h>
> +#endif
> +
> /* `bindgen` gets confused at certain things. */
> const size_t RUST_CONST_HELPER_ARCH_SLAB_MINALIGN = ARCH_SLAB_MINALIGN;
> const size_t RUST_CONST_HELPER_PAGE_SIZE = PAGE_SIZE;
>
> --
> 2.48.1.711.g2feabab25a-goog
>

--
Simona Vetter
Software Engineer, Intel Corporation