Deny unsafe_op_in_unsafe_fn by default

Edition 2024 requires that we avoid this. There is a lot of code that
will need to be adjusted, so start the process here.

Author: tgross35

builtins-test-intrinsics/src/main.rs

@@ -647,14 +647,14 @@ fn something_with_a_dtor(f: &dyn Fn()) {
     f();
 }
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 #[cfg(not(thumb))]
 fn main(_argc: core::ffi::c_int, _argv: *const *const u8) -> core::ffi::c_int {
     run();
     0
 }
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 #[cfg(thumb)]
 pub fn _start() -> ! {
     run();
@@ -667,30 +667,30 @@ pub fn _start() -> ! {
 extern "C" {}
 
 // ARM targets need these symbols
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub fn __aeabi_unwind_cpp_pr0() {}
 
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub fn __aeabi_unwind_cpp_pr1() {}
 
 #[cfg(not(any(windows, target_os = "cygwin")))]
 #[allow(non_snake_case)]
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub fn _Unwind_Resume() {}
 
 #[cfg(not(any(windows, target_os = "cygwin")))]
 #[lang = "eh_personality"]
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub extern "C" fn eh_personality() {}
 
 #[cfg(any(all(windows, target_env = "gnu"), target_os = "cygwin"))]
 mod mingw_unwinding {
-    #[no_mangle]
+    #[unsafe(no_mangle)]
     pub fn rust_eh_personality() {}
-    #[no_mangle]
+    #[unsafe(no_mangle)]
     pub fn rust_eh_unwind_resume() {}
-    #[no_mangle]
+    #[unsafe(no_mangle)]
     pub fn rust_eh_register_frames() {}
-    #[no_mangle]
+    #[unsafe(no_mangle)]
     pub fn rust_eh_unregister_frames() {}
 }

src/lib.rs

@@ -22,6 +22,9 @@
 #![allow(clippy::manual_swap)]
 // Support compiling on both stage0 and stage1 which may differ in supported stable features.
 #![allow(stable_features)]
+// By default, disallow this as it is forbidden in edition 2024. There is a lot of unsafe code to
+// be migrated, however, so exceptions exist.
+#![deny(unsafe_op_in_unsafe_fn)]
 
 // We disable #[no_mangle] for tests so that we can verify the test results
 // against the native compiler-rt implementations of the builtins.

src/macros.rs

@@ -256,7 +256,7 @@ macro_rules! intrinsics {
 
         #[cfg(all(target_vendor = "apple", any(target_arch = "x86", target_arch = "x86_64"), not(feature = "mangled-names")))]
         mod $name {
-            #[no_mangle]
+            #[unsafe(no_mangle)]
             #[cfg_attr(not(any(all(windows, target_env = "gnu"), target_os = "cygwin")), linkage = "weak")]
             $(#[$($attr)*])*
             extern $abi fn $name( $($argname: u16),* ) $(-> $ret)? {
@@ -292,7 +292,7 @@ macro_rules! intrinsics {
 
         #[cfg(all(target_vendor = "apple", any(target_arch = "x86", target_arch = "x86_64"), not(feature = "mangled-names")))]
         mod $name {
-            #[no_mangle]
+            #[unsafe(no_mangle)]
             #[cfg_attr(not(any(all(windows, target_env = "gnu"), target_os = "cygwin")), linkage = "weak")]
             $(#[$($attr)*])*
             extern $abi fn $name( $($argname: $ty),* ) -> u16 {
@@ -333,7 +333,7 @@ macro_rules! intrinsics {
 
         #[cfg(all(target_arch = "arm", not(feature = "mangled-names")))]
         mod $name {
-            #[no_mangle]
+            #[unsafe(no_mangle)]
             #[cfg_attr(not(any(all(windows, target_env = "gnu"), target_os = "cygwin")), linkage = "weak")]
             $(#[$($attr)*])*
             extern $abi fn $name( $($argname: $ty),* ) $(-> $ret)? {
@@ -343,7 +343,7 @@ macro_rules! intrinsics {
 
         #[cfg(all(target_arch = "arm", not(feature = "mangled-names")))]
         mod $alias {
-            #[no_mangle]
+            #[unsafe(no_mangle)]
             #[cfg_attr(not(any(all(windows, target_env = "gnu"), target_os = "cygwin")), linkage = "weak")]
             $(#[$($attr)*])*
             extern "aapcs" fn $alias( $($argname: $ty),* ) $(-> $ret)? {
@@ -410,7 +410,7 @@ macro_rules! intrinsics {
         #[cfg(all(feature = "mem", not(feature = "mangled-names")))]
         mod $name {
             $(#[$($attr)*])*
-            #[no_mangle]
+            #[unsafe(no_mangle)]
             #[cfg_attr(not(any(all(windows, target_env = "gnu"), target_os = "cygwin")), linkage = "weak")]
             unsafe extern $abi fn $name( $($argname: $ty),* ) $(-> $ret)? {
                 super::$name($($argname),*)
@@ -502,7 +502,7 @@ macro_rules! intrinsics {
         #[cfg(not(feature = "mangled-names"))]
         mod $name {
             $(#[$($attr)*])*
-            #[no_mangle]
+            #[unsafe(no_mangle)]
             #[cfg_attr(not(any(all(windows, target_env = "gnu"), target_os = "cygwin")), linkage = "weak")]
             $(unsafe $($empty)?)? extern $abi fn $name( $($argname: $ty),* ) $(-> $ret)? {
                 super::$name($($argname),*)

src/mem/mod.rs

@@ -1,5 +1,6 @@
 // Trying to satisfy clippy here is hopeless
 #![allow(clippy::style)]
+#![allow(unsafe_op_in_unsafe_fn)]
 
 #[allow(warnings)]
 #[cfg(target_pointer_width = "16")]

src/x86_64.rs

@@ -44,7 +44,7 @@ intrinsics! {
 // HACK(https://github.com/rust-lang/rust/issues/62785): x86_64-unknown-uefi needs special LLVM
 // support unless we emit the _fltused
 mod _fltused {
-    #[no_mangle]
+    #[unsafe(no_mangle)]
     #[used]
     #[cfg(target_os = "uefi")]
     static _fltused: i32 = 0;