cgen: support a `[_naked]` fn attribute (#10418)

vlib/v/checker/checker.v

@@ -7260,7 +7260,7 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 		&& (node.is_method || node.name !in ['panic', 'exit']) {
 		if c.inside_anon_fn {
 			c.error('missing return at the end of an anonymous function', node.pos)
-		} else {
+		} else if !node.attrs.contains('_naked') {
 			c.error('missing return at end of function `$node.name`', node.pos)
 		}
 	}

vlib/v/gen/c/fn.v

@@ -332,7 +332,8 @@ fn (mut g Gen) gen_fn_decl(node &ast.FnDecl, skip bool) {
 	} else {
 		g.defer_stmts = []
 	}
-	if node.return_type != ast.void_type && node.stmts.len > 0 && node.stmts.last() !is ast.Return {
+	if node.return_type != ast.void_type && node.stmts.len > 0 && node.stmts.last() !is ast.Return
+		&& !node.attrs.contains('_naked') {
 		default_expr := g.type_default(node.return_type)
 		// TODO: perf?
 		if default_expr == '{0}' {
@@ -1354,6 +1355,9 @@ fn (mut g Gen) write_fn_attrs(attrs []ast.Attr) string {
 				// repeated invocations of the function with the same argument values.
 				g.write('__attribute__((const)) ')
 			}
+			'_naked' {
+				g.write('__attribute__((naked)) ')
+			}
 			'windows_stdcall' {
 				// windows attributes (msvc/mingw)
 				// prefixed by windows to indicate they're for advanced users only and not really supported by V.

vlib/v/parser/fn.v

@@ -342,7 +342,8 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	short_fn_name := name
 	is_main := short_fn_name == 'main' && p.mod == 'main'
 	mut is_test := (short_fn_name.starts_with('test_') || short_fn_name.starts_with('testsuite_'))
-		&& (p.file_base.ends_with('_test.v') || p.file_base.ends_with('_test.vv'))
+		&& (p.file_base.ends_with('_test.v')
+		|| p.file_base.all_before_last('.v').all_before_last('.').ends_with('_test'))
 
 	// Register
 	if is_method {

vlib/v/parser/parser.v

@@ -900,7 +900,7 @@ fn (mut p Parser) asm_stmt(is_top_level bool) ast.AsmStmt {
 			p.check(.name)
 		}
 		// dots are part of instructions for some riscv extensions
-		if arch in [.rv32, .rv64] {
+		if arch in [.rv32, .rv64, .amd64] {
 			for p.tok.kind == .dot {
 				name += '.'
 				p.next()

vlib/v/tests/assembly/naked_attr_test.amd64.v

@@ -0,0 +1,14 @@
+[_naked]
+fn naked_fn() {
+	asm amd64 {
+		push rbp
+		mov rbp, rsp
+		mov rsp, rbp
+		pop rbp
+		ret
+	}
+}
+
+fn test_naked_attr() {
+	naked_fn()
+}

vlib/v/tests/assembly/naked_attr_test.i386.v

@@ -0,0 +1,14 @@
+[_naked]
+fn naked_fn() {
+	asm i386 {
+		push ebp
+		mov ebp, esp
+		mov esp, ebp
+		pop ebp
+		ret
+	}
+}
+
+fn test_naked_attr() {
+	naked_fn()
+}