bootstrap `naked_asm!` for `compiler-builtins`

in this commit, `naked_asm!` is an alias for `asm!` with one difference: `options(noreturn)` is always enabled by `naked_asm!`. That makes it future-compatible for when `naked_asm!` starts disallowing `options(noreturn)` later.

compiler/rustc_builtin_macros/src/asm.rs

@@ -812,6 +812,44 @@ pub(super) fn expand_asm<'cx>(
     })
 }
 
+pub(super) fn expand_naked_asm<'cx>(
+    ecx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> MacroExpanderResult<'cx> {
+    ExpandResult::Ready(match parse_args(ecx, sp, tts, false) {
+        Ok(args) => {
+            let ExpandResult::Ready(mac) = expand_preparsed_asm(ecx, args) else {
+                return ExpandResult::Retry(());
+            };
+            let expr = match mac {
+                Ok(mut inline_asm) => {
+                    // for future compatibility, we always set the NORETURN option.
+                    //
+                    // When we turn `asm!` into `naked_asm!` with this implementation, we can drop
+                    // the `options(noreturn)`, which makes the upgrade smooth when `naked_asm!`
+                    // starts disallowing the `noreturn` option in the future
+                    inline_asm.options |= ast::InlineAsmOptions::NORETURN;
+
+                    P(ast::Expr {
+                        id: ast::DUMMY_NODE_ID,
+                        kind: ast::ExprKind::InlineAsm(P(inline_asm)),
+                        span: sp,
+                        attrs: ast::AttrVec::new(),
+                        tokens: None,
+                    })
+                }
+                Err(guar) => DummyResult::raw_expr(sp, Some(guar)),
+            };
+            MacEager::expr(expr)
+        }
+        Err(err) => {
+            let guar = err.emit();
+            DummyResult::any(sp, guar)
+        }
+    })
+}
+
 pub(super) fn expand_global_asm<'cx>(
     ecx: &'cx mut ExtCtxt<'_>,
     sp: Span,

compiler/rustc_builtin_macros/src/lib.rs

@@ -94,6 +94,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
         line: source_util::expand_line,
         log_syntax: log_syntax::expand_log_syntax,
         module_path: source_util::expand_mod,
+        naked_asm: asm::expand_naked_asm,
         option_env: env::expand_option_env,
         pattern_type: pattern_type::expand,
         std_panic: edition_panic::expand_panic,

compiler/rustc_span/src/symbol.rs

@@ -1254,6 +1254,7 @@ symbols! {
         mut_preserve_binding_mode_2024,
         mut_ref,
         naked,
+        naked_asm,
         naked_functions,
         name,
         names,

library/core/src/arch.rs

@@ -26,6 +26,20 @@ pub macro asm("assembly template", $(operands,)* $(options($(option),*))?) {
     /* compiler built-in */
 }
 
+/// Inline assembly used in combination with `#[naked]` functions.
+///
+/// Refer to [Rust By Example] for a usage guide and the [reference] for
+/// detailed information about the syntax and available options.
+///
+/// [Rust By Example]: https://doc.rust-lang.org/nightly/rust-by-example/unsafe/asm.html
+/// [reference]: https://doc.rust-lang.org/nightly/reference/inline-assembly.html
+#[unstable(feature = "naked_functions", issue = "90957")]
+#[rustc_builtin_macro]
+#[cfg(not(bootstrap))]
+pub macro naked_asm("assembly template", $(operands,)* $(options($(option),*))?) {
+    /* compiler built-in */
+}
+
 /// Module-level inline assembly.
 ///
 /// Refer to [Rust By Example] for a usage guide and the [reference] for

tests/ui/asm/naked-functions-inline.rs

@@ -2,37 +2,37 @@
 #![feature(naked_functions)]
 #![crate_type = "lib"]
 
-use std::arch::asm;
+use std::arch::naked_asm;
 
 #[naked]
 pub unsafe extern "C" fn inline_none() {
-    asm!("", options(noreturn));
+    naked_asm!("");
 }
 
 #[naked]
 #[inline]
 //~^ ERROR [E0736]
 pub unsafe extern "C" fn inline_hint() {
-    asm!("", options(noreturn));
+    naked_asm!("");
 }
 
 #[naked]
 #[inline(always)]
 //~^ ERROR [E0736]
 pub unsafe extern "C" fn inline_always() {
-    asm!("", options(noreturn));
+    naked_asm!("");
 }
 
 #[naked]
 #[inline(never)]
 //~^ ERROR [E0736]
 pub unsafe extern "C" fn inline_never() {
-    asm!("", options(noreturn));
+    naked_asm!("");
 }
 
 #[naked]
 #[cfg_attr(all(), inline(never))]
 //~^ ERROR [E0736]
 pub unsafe extern "C" fn conditional_inline_never() {
-    asm!("", options(noreturn));
+    naked_asm!("");
 }