naked_asm: emit a label starting with func_end

The `cargo asm` tool pattern matches on such labels to figure out where functions end: normal functions generated by LLVM always do have such a label. We don't guarantee that naked functions emit such a label, but having `cargo asm` work is convenient

Author: folkertdev

compiler/rustc_codegen_ssa/src/mir/naked_asm.rs

@@ -228,6 +228,9 @@ fn prefix_and_suffix<'tcx>(
             writeln!(begin, "{asm_name}:").unwrap();
 
             writeln!(end).unwrap();
+            // emit a label starting with `func_end` for `cargo asm` and other tooling that might
+            // pattern match on assembly generated by LLVM.
+            writeln!(end, ".Lfunc_end_{asm_name}:").unwrap();
             writeln!(end, ".size {asm_name}, . - {asm_name}").unwrap();
             writeln!(end, ".popsection").unwrap();
             if !arch_suffix.is_empty() {
@@ -246,6 +249,7 @@ fn prefix_and_suffix<'tcx>(
             writeln!(begin, "{asm_name}:").unwrap();
 
             writeln!(end).unwrap();
+            writeln!(end, ".Lfunc_end_{asm_name}:").unwrap();
             writeln!(end, ".popsection").unwrap();
             if !arch_suffix.is_empty() {
                 writeln!(end, "{}", arch_suffix).unwrap();
@@ -263,6 +267,7 @@ fn prefix_and_suffix<'tcx>(
             writeln!(begin, "{asm_name}:").unwrap();
 
             writeln!(end).unwrap();
+            writeln!(end, ".Lfunc_end_{asm_name}:").unwrap();
             writeln!(end, ".popsection").unwrap();
             if !arch_suffix.is_empty() {
                 writeln!(end, "{}", arch_suffix).unwrap();
@@ -287,6 +292,7 @@ fn prefix_and_suffix<'tcx>(
             writeln!(end).unwrap();
             // .size is ignored for function symbols, so we can skip it
             writeln!(end, "end_function").unwrap();
+            writeln!(end, ".Lfunc_end_{asm_name}:").unwrap();
         }
         BinaryFormat::Xcoff => {
             // the LLVM XCOFFAsmParser is extremely incomplete and does not implement many of the

tests/assembly-llvm/naked-functions/wasm32.rs

@@ -21,6 +21,7 @@ use minicore::*;
 // CHECK: .functype nop () -> ()
 // CHECK-NOT: .size
 // CHECK: end_function
+// CHECK-LABEL: .Lfunc_end_nop:
 #[no_mangle]
 #[unsafe(naked)]
 extern "C" fn nop() {