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

Alice Ryhl
2025-02-28T12:40:17Z

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>
---
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