print: use new #[export] macro for rust_fmt_argument

This moves the rust_fmt_argument function over to use the new #[export]
macro, which will verify at compile-time that the function signature
matches what is in the header file.

Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Tamir Duberstein <tamird@gmail.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20250303-export-macro-v3-4-41fbad85a27f@google.com
[ Removed period as requested by Andy. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

include/linux/sprintf.h

@@ -24,4 +24,7 @@ __scanf(2, 0) int vsscanf(const char *, const char *, va_list);
 extern bool no_hash_pointers;
 int no_hash_pointers_enable(char *str);
 
+/* Used for Rust formatting ('%pA') */
+char *rust_fmt_argument(char *buf, char *end, const void *ptr);
+
 #endif	/* _LINUX_KERNEL_SPRINTF_H */

lib/vsprintf.c

@@ -2284,9 +2284,6 @@ int __init no_hash_pointers_enable(char *str)
 }
 early_param("no_hash_pointers", no_hash_pointers_enable);
 
-/* Used for Rust formatting ('%pA'). */
-char *rust_fmt_argument(char *buf, char *end, const void *ptr);
-
 /*
  * Show a '%p' thing.  A kernel extension is that the '%p' is followed
  * by an extra set of alphanumeric characters that are extended format

rust/kernel/print.rs

@@ -8,13 +8,14 @@
 
 use crate::{
     ffi::{c_char, c_void},
+    prelude::*,
     str::RawFormatter,
 };
 use core::fmt;
 
 // Called from `vsprintf` with format specifier `%pA`.
 #[expect(clippy::missing_safety_doc)]
-#[no_mangle]
+#[export]
 unsafe extern "C" fn rust_fmt_argument(
     buf: *mut c_char,
     end: *mut c_char,