[PATCH] rust: kernel: Mark rust_fmt_argument as extern "C"

[David Gow]

The rust_fmt_argument function is called from printk() to handle the %pA
format specifier.

Since it's called from C, we should mark it extern "C" to make sure it's
ABI compatible.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 247b365dc8dc ("rust: add `kernel` crate")
Signed-off-by: David Gow <davidgow@xxxxxxxxxx>
---

See discussion in:
https://github.com/Rust-for-Linux/linux/pull/967
and
https://github.com/Rust-for-Linux/linux/pull/966

---
 rust/kernel/print.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs
index 30103325696d..ec457f0952fe 100644
--- a/rust/kernel/print.rs
+++ b/rust/kernel/print.rs
@@ -18,7 +18,7 @@ use crate::bindings;
 
 // Called from `vsprintf` with format specifier `%pA`.
 #[no_mangle]
-unsafe fn rust_fmt_argument(buf: *mut c_char, end: *mut c_char, ptr: *const c_void) -> *mut c_char {
+unsafe extern "C" fn rust_fmt_argument(buf: *mut c_char, end: *mut c_char, ptr: *const c_void) -> *mut c_char {
     use fmt::Write;
     // SAFETY: The C contract guarantees that `buf` is valid if it's less than `end`.
     let mut w = unsafe { RawFormatter::from_ptrs(buf.cast(), end.cast()) };
-- 
2.39.1.581.gbfd45094c4-goog