From 3a9486b7712f0328a96fe33449ce191385096f75 Mon Sep 17 00:00:00 2001
From: Andrew Mackenzie <andrew@mackenzie-serres.net>
Date: Wed, 16 Sep 2026 08:21:45 +0200
Subject: [PATCH] Provide wcslen for x86_64-unknown-uefi target

The uefi crate's FileInfo::from_uefi and RegularFile::get_info reference
wcslen for wide string length calculation. The x86_64-unknown-uefi target
has no C runtime providing this symbol, causing a linker error.

Add a simple wcslen implementation to the UEFI bootloader binary.
Use #[unsafe(no_mangle)] for compatibility with Rust 2024 edition.

Fixes: https://github.com/rust-osdev/bootloader/issues/579
---
 uefi/src/main.rs | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/uefi/src/main.rs b/uefi/src/main.rs
index 13a28526..db128a34 100644
--- a/uefi/src/main.rs
+++ b/uefi/src/main.rs
@@ -445,3 +445,20 @@ fn panic(info: &core::panic::PanicInfo) -> ! {
         unsafe { asm!("cli; hlt") };
     }
 }
+
+/// Provide `wcslen` for the `uefi` crate which needs it for wide string
+/// handling (e.g. `FileInfo::from_uefi`). The `x86_64-unknown-uefi` target
+/// has no C runtime, so this must be supplied explicitly.
+///
+/// See: https://github.com/rust-osdev/bootloader/issues/579
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn wcslen(s: *const u16) -> usize {
+    let mut len = 0;
+    // SAFETY: caller guarantees `s` points to a null-terminated wide string.
+    unsafe {
+        while *s.add(len) != 0 {
+            len += 1;
+        }
+    }
+    len
+}