diff --git a/cmd/v/v.v b/cmd/v/v.v
index a3e6d8ac2b..9ff25fa871 100644
--- a/cmd/v/v.v
+++ b/cmd/v/v.v
@@ -104,6 +104,8 @@ fn main() {
 		else {}
 	}
 	if command in ['run', 'build'] || command.ends_with('.v') || os.exists(command) {
+		println('command')
+		println(prefs.path)
 		builder.compile(command, prefs)
 		return
 	}
@@ -177,6 +179,10 @@ fn parse_args(args []string) (&pref.Preferences, string) {
 		res.path = args[command_pos+1]
 		res.run_args = args[command_pos+1..]
 	}
+	if command == 'build' {
+		res.build_mode = .build_module
+		res.path = args[command_pos+1]
+	}
 	if res.is_verbose {
 		println('setting pref.path to "$res.path"')
 	}
diff --git a/vlib/crypto/rand/rand.v b/vlib/crypto/rand/rand.v
index 0b822c37a1..f8f1c66cb2 100644
--- a/vlib/crypto/rand/rand.v
+++ b/vlib/crypto/rand/rand.v
@@ -10,12 +10,18 @@ const (
 
 // NOTE: temp until we have []bytes(buff)
 fn c_array_to_bytes_tmp(len, buffer voidptr) []byte {
+
 	mut arr := []byte
+	arr = make(len, 1, 1)
+	arr.data = buffer
+	/*
+
 	arr = array {
 		len: len
 		cap: 1
 		element_size: 1
 		data: buffer
 	}
+	*/
 	return arr
 }
diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index 908c7f86ac..e03080ea8b 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -185,6 +185,7 @@ pub:
 	rec_mut       bool // is receiver mutable
 	is_c          bool
 	no_body       bool // just a definition `fn C.malloc()`
+	is_builtin    bool // this function is defined in builtin/strconv
 	pos           token.Position
 }
 
diff --git a/vlib/v/builder/cc.v b/vlib/v/builder/cc.v
index 4fa1962192..e01d094867 100644
--- a/vlib/v/builder/cc.v
+++ b/vlib/v/builder/cc.v
@@ -301,6 +301,11 @@ fn (v mut Builder) cc() {
 	// add all flags (-I -l -L etc) not .o files
 	a << cflags.c_options_without_object_files()
 	a << libs
+
+	if v.pref.show_cc {
+		a << pref.default_module_path + '/cache/vlib/builtin.o'
+	}
+
 	// Without these libs compilation will fail on Linux
 	// || os.user_os() == 'linux'
 	if !v.pref.is_bare && v.pref.build_mode != .build_module && v.pref.os in [.linux, .freebsd, .openbsd, .netbsd, .dragonfly, .solaris, .haiku] {
diff --git a/vlib/v/builder/compile.v b/vlib/v/builder/compile.v
index 4310424daf..e5521a0586 100644
--- a/vlib/v/builder/compile.v
+++ b/vlib/v/builder/compile.v
@@ -31,7 +31,7 @@ pub fn compile(command string, pref &pref.Preferences) {
 	mut b := new_builder(pref)
 	if pref.is_verbose {
 		println('builder.compile() pref:')
-		println(pref)
+		// println(pref)
 	}
 	mut tmark := benchmark.new_benchmark()
 	mut files := []string
@@ -65,7 +65,7 @@ pub fn compile(command string, pref &pref.Preferences) {
 		mut out_name_c := get_vtmp_filename(pref.out_name, '.tmp.c')
 		if pref.is_so {
 			out_name_c = get_vtmp_filename(pref.out_name, '.tmp.so.c')
-		}	   	   
+		}
 		b.build_c(files, out_name_c)
 		b.cc()
 	}
@@ -145,6 +145,13 @@ fn (v mut Builder) set_module_lookup_paths() {
 }
 
 pub fn (v Builder) get_builtin_files() []string {
+	if v.pref.build_mode == .build_module && v.pref.path == 'vlib/builtin' {		// .contains('builtin/' +  location {
+		// We are already building builtin.o, no need to import them again
+		if v.pref.is_verbose {
+			println('skipping builtin modules for builtin.o')
+		}
+		return []
+	}
 	// println('get_builtin_files() lookuppath:')
 	// println(v.pref.lookup_path)
 	// Lookup for built-in folder in lookup path.
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 5b173fe047..a4f6ea3e18 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -519,14 +519,19 @@ pub fn (c mut Checker) selector_expr(selector_expr mut ast.SelectorExpr) table.T
 // TODO: non deferred
 pub fn (c mut Checker) return_stmt(return_stmt mut ast.Return) {
 	c.expected_type = c.fn_return_type
-	if return_stmt.exprs.len == 0 {
+	if return_stmt.exprs.len > 0 && c.fn_return_type == table.void_type {
+		c.error('1too many arguments to return, current function does not return anything',
+			return_stmt.pos)
 		return
 	}
-	if return_stmt.exprs.len > 0 && c.fn_return_type == table.void_type {
-		c.error('too many arguments to return, current function does not return anything',
+	else if return_stmt.exprs.len == 0 && c.fn_return_type != table.void_type {
+		c.error('too few arguments to return',
 			return_stmt.pos)
 		return
 	}
+	if return_stmt.exprs.len == 0 {
+		return
+	}
 	expected_type := c.fn_return_type
 	expected_type_sym := c.table.get_type_symbol(expected_type)
 	exp_is_optional := table.type_is(expected_type, .optional)
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index a036c6ad10..df4c948b23 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -112,7 +112,10 @@ pub fn cgen(files []ast.File, table &table.Table, pref &pref.Preferences) string
 	}
 	g.write_variadic_types()
 	// g.write_str_definitions()
-	g.write_init_function()
+	if g.pref.build_mode != .build_module {
+		// no init in builtin.o
+		g.write_init_function()
+	}
 	if g.is_test {
 		g.write_tests_main()
 	}
@@ -138,18 +141,25 @@ pub fn (g mut Gen) init() {
 	g.write_builtin_types()
 	g.write_typedef_types()
 	g.write_typeof_functions()
-	g.write_str_definitions()
+	if g.pref.build_mode != .build_module {
+		// _STR functions should not be defined in builtin.o
+		g.write_str_fn_definitions()
+	}
 	g.write_sorted_types()
 	g.write_multi_return_types()
 	g.definitions.writeln('// end of definitions #endif')
 	//
 	g.stringliterals.writeln('')
 	g.stringliterals.writeln('// >> string literal consts')
-	g.stringliterals.writeln('void vinit_string_literals(){')
+	if g.pref.build_mode != .build_module {
+		g.stringliterals.writeln('void vinit_string_literals(){')
+	}
 }
 
 pub fn (g mut Gen) finish() {
-	g.stringliterals.writeln('}')
+	if g.pref.build_mode != .build_module {
+		g.stringliterals.writeln('}')
+	}
 	g.stringliterals.writeln('// << string literal consts')
 	g.stringliterals.writeln('')
 }
@@ -352,7 +362,9 @@ fn (g mut Gen) stmt(node ast.Stmt) {
 			g.writeln(';')
 		}
 		ast.ConstDecl {
+			// if g.pref.build_mode != .build_module {
 			g.const_decl(it)
+			// }
 		}
 		ast.CompIf {
 			g.comp_if(it)
@@ -808,6 +820,9 @@ fn (g mut Gen) gen_fn_decl(it ast.FnDecl) {
 		} else {
 			name = c_name(name)
 		}
+		// if g.pref.show_cc && it.is_builtin {
+		// println(name)
+		// }
 		// type_name := g.table.Type_to_str(it.return_type)
 		type_name := g.typ(it.return_type)
 		g.write('$type_name ${name}(')
@@ -832,8 +847,9 @@ fn (g mut Gen) gen_fn_decl(it ast.FnDecl) {
 */
 	//
 	g.fn_args(it.args, it.is_variadic)
-	if it.no_body {
+	if it.no_body || (g.pref.show_cc && it.is_builtin) {
 		// Just a function header.
+		// Builtin function bodies are defined in builtin.o
 		g.definitions.writeln(');')
 		g.writeln(');')
 		return
@@ -1437,8 +1453,8 @@ fn (g mut Gen) infix_expr(node ast.InfixExpr) {
 		g.write(',')
 		g.expr(node.right)
 		g.write(')')
-	} else if node.op in [.plus, .minus, .mul, .div, .mod] && (left_sym.name[0].is_capital() || left_sym.name.contains('.')) &&
-		left_sym.kind != .alias {
+	} else if node.op in [.plus, .minus, .mul, .div, .mod] && (left_sym.name[0].is_capital() ||
+		left_sym.name.contains('.')) && left_sym.kind != .alias {
 		// !left_sym.is_number() {
 		g.write(g.typ(node.left_type))
 		g.write('_')
@@ -1903,7 +1919,9 @@ fn (g mut Gen) const_decl(node ast.ConstDecl) {
 			}
 			ast.StringLiteral {
 				g.definitions.writeln('string _const_$name; // a string literal, inited later')
-				g.stringliterals.writeln('\t_const_$name = $val;')
+				if g.pref.build_mode != .build_module {
+					g.stringliterals.writeln('\t_const_$name = $val;')
+				}
 			}
 			else {
 				// Initialize more complex consts in `void _vinit(){}`
@@ -2127,7 +2145,7 @@ fn (g mut Gen) write_init_function() {
 	}
 }
 
-fn (g mut Gen) write_str_definitions() {
+fn (g mut Gen) write_str_fn_definitions() {
 	// _STR function can't be defined in vlib
 	g.writeln('
 string _STR(const char *fmt, ...) {
diff --git a/vlib/v/gen/cheaders.v b/vlib/v/gen/cheaders.v
index 6ebe05a0c4..cd081770ec 100644
--- a/vlib/v/gen/cheaders.v
+++ b/vlib/v/gen/cheaders.v
@@ -222,7 +222,12 @@ void _vcleanup();
 #include <intrin.h>
 #pragma intrinsic(_umul128)
 #endif
-const uint64_t _wyp0=0xa0761d6478bd642full, _wyp1=0xe7037ed1a0b428dbull;
+
+//const uint64_t _wyp0=0xa0761d6478bd642full, _wyp1=0xe7037ed1a0b428dbull;
+#define _wyp0 ((uint64_t)0xa0761d6478bd642full)
+#define _wyp1 ((uint64_t)0xe7037ed1a0b428dbull)
+
+
 #if defined(__GNUC__) || defined(__INTEL_COMPILER) || defined(__clang__)
 #define _likely_(x) __builtin_expect(x, 1)
 #else
diff --git a/vlib/v/parser/fn.v b/vlib/v/parser/fn.v
index 130556c3f1..c268f5b4e5 100644
--- a/vlib/v/parser/fn.v
+++ b/vlib/v/parser/fn.v
@@ -196,14 +196,16 @@ fn (p mut Parser) fn_decl() ast.FnDecl {
 		is_pub: is_pub
 		is_variadic: is_variadic
 		receiver: ast.Field{
-		name: rec_name
-		typ: rec_type
-	}
+			name: rec_name
+			typ: rec_type
+		}
 		is_method: is_method
 		rec_mut: rec_mut
 		is_c: is_c
 		no_body: no_body
 		pos: p.tok.position()
+		is_builtin: p.builtin_mod || p.mod in ['math', 'strconv', 'strconv.ftoa', 'hash.wyhash',
+			'math.bits', 'strings']
 	}
 }