Add va_arg()

include/stdarg.h

@@ -15,6 +15,30 @@ typedef __va_elem va_list[1];
 
 #define va_end(ap)
 
+static void *__va_arg_gp(__va_elem *ap) {
+  void *r = (char *)ap->reg_save_area + ap->gp_offset;
+  ap->gp_offset += 8;
+  return r;
+}
+
+static void *__va_arg_fp(__va_elem *ap) {
+  void *r = (char *)ap->reg_save_area + ap->fp_offset;
+  ap->fp_offset += 8;
+  return r;
+}
+
+static void *__va_arg_mem(__va_elem *ap) {
+  1 / 0; // not implemented
+}
+
+#define va_arg(ap, type)                        \
+  ({                                            \
+    int klass = __builtin_reg_class(type);      \
+    *(type *)(klass == 0 ? __va_arg_gp(ap) :    \
+              klass == 1 ? __va_arg_fp(ap) :    \
+              __va_arg_mem(ap));                \
+  })
+
 #define __GNUC_VA_LIST 1
 typedef va_list __gnuc_va_list;
 

parse.c

@@ -2246,6 +2246,7 @@ static Node *funcall(Token **rest, Token *tok, Node *fn) {
 //         | "sizeof" unary
 //         | "_Alignof" "(" type-name ")"
 //         | "_Alignof" unary
+//         | "__builtin_reg_class" "(" type-name ")"
 //         | ident
 //         | str
 //         | num
@@ -2290,6 +2291,18 @@ static Node *primary(Token **rest, Token *tok) {
     return new_ulong(node->ty->align, tok);
   }
 
+  if (equal(tok, "__builtin_reg_class")) {
+    tok = skip(tok->next, "(");
+    Type *ty = typename(&tok, tok);
+    *rest = skip(tok, ")");
+
+    if (is_integer(ty) || ty->kind == TY_PTR)
+      return new_num(0, start);
+    if (is_flonum(ty))
+      return new_num(1, start);
+    return new_num(2, start);
+  }
+
   if (tok->kind == TK_IDENT) {
     // Variable or enum constant
     VarScope *sc = find_var(tok);

test/varargs.c

@@ -0,0 +1,37 @@
+#include "test.h"
+#include <stdarg.h>
+
+int sum1(int x, ...) {
+  va_list ap;
+  va_start(ap, x);
+
+  for (;;) {
+    int y = va_arg(ap, int);
+    if (y == 0)
+      return x;
+    x += y;
+  }
+}
+
+int sum2(int x, ...) {
+  va_list ap;
+  va_start(ap, x);
+
+  for (;;) {
+    double y = va_arg(ap, double);
+    x += y;
+
+    int z = va_arg(ap, int);
+    if (z == 0)
+      return x;
+    x += z;
+  }
+}
+
+int main() {
+  ASSERT(6, sum1(1, 2, 3, 0));
+  ASSERT(21, sum2(1, 2.0, 3, 4.0, 5, 6.0, 0));
+
+  printf("OK\n");
+  return 0;
+}