Fix handling variadic parameters

  * `typedef void **va_list`
  * Must layout saved registers to the bottom of stack frame

include/stdarg.h

@@ -22,6 +22,14 @@ typedef void **va_list;
 #define va_arg(ap, type)  (*(type*)(ap)++)  // Assume little endian
 #define va_copy(dst,src)  (dst = src)
 
+#elif defined(__riscv)
+typedef void **va_list;
+
+#define va_start(ap,p)    __builtin_va_start(ap,&(p))
+#define va_end(ap)        /*(void)*/(ap = 0)
+#define va_arg(ap, type)  ((ap) += 1, *(type*)((ap) - 1))  // Assume little endian
+#define va_copy(dst,src)  (dst = src)
+
 #else  // not __APPLE__ nor __aarch64__
 
 #include <stdint.h>

src/cc/arch/riscv64/emit_code.c

@@ -356,17 +356,42 @@ static void emit_varinfo(const VarInfo *varinfo, const Initializer *init) {
 
 ////////////////////////////////////////////////
 
+static const char *kRegParam64s[] = {A0, A1, A2, A3, A4, A5, A6, A7};
+
 static bool is_asm(Stmt *stmt) {
   return stmt->kind == ST_ASM;
 }
 
+static int put_vaarg_params(Function *func) {
+  assert(func->type->func.vaargs);
+#if VAARG_ON_STACK
+  return;
+#else
+  RegParamInfo iparams[MAX_REG_ARGS];
+  RegParamInfo fparams[MAX_FREG_ARGS];
+  int iparam_count = 0;
+  int fparam_count = 0;
+  enumerate_register_params(func, iparams, MAX_REG_ARGS, fparams, MAX_FREG_ARGS,
+                            &iparam_count, &fparam_count);
+
+  int size = 0;
+  int n = MAX_REG_ARGS - iparam_count;
+  if (n > 0) {
+    size = n * POINTER_SIZE;
+    ADDI(SP, SP, IM(-size));
+    for (int i = iparam_count, offset = 0; i < MAX_REG_ARGS; ++i, offset += POINTER_SIZE)
+      SD(kRegParam64s[i], IMMEDIATE_OFFSET(offset, SP));
+  }
+  return size;
+#endif
+}
+
 static void move_params_to_assigned(Function *func) {
   extern const char *kReg64s[];
   extern const int ArchRegParamMapping[];
   extern const char *kFReg64s[];
 
   // static const char *kRegParam32s[] = {W0, W1, W2, W3, W4, W5, W6, W7};
-  static const char *kRegParam64s[] = {A0, A1, A2, A3, A4, A5, A6, A7};
   // static const char **kRegParamTable[] = {kRegParam32s, kRegParam32s, kRegParam32s, kRegParam64s};
   // const char *kFRegParam32s[] = {S0, S1, S2, S3, S4, S5, S6, S7};
   const char *kFRegParam64s[] = {FA0, FA1, FA2, FA3, FA4, FA5, FA6, FA7};
@@ -426,22 +451,6 @@ static void move_params_to_assigned(Function *func) {
       }
     }
   }
-
-#if VAARG_ON_STACK
-  bool vaargs = false;
-#else
-  bool vaargs = func->type->func.vaargs;
-#endif
-  if (vaargs) {
-    for (int i = iparam_count; i < MAX_REG_ARGS; ++i) {
-      int offset = (i - MAX_REG_ARGS - MAX_FREG_ARGS) * POINTER_SIZE;
-      SD(kRegParam64s[i], IMMEDIATE_OFFSET(offset, FP));
-    }
-    // for (int i = fparam_count; i < MAX_FREG_ARGS; ++i) {
-    //   int offset = (i - MAX_FREG_ARGS) * POINTER_SIZE;
-    //   SD(kFRegParam64s[i], IMMEDIATE_OFFSET(offset, FP));
-    // }
-  }
 }
 
 static void emit_defun(Function *func) {
@@ -491,7 +500,15 @@ static void emit_defun(Function *func) {
   bool fp_saved = false;  // Frame pointer saved?
   bool ra_saved = false;  // Return Address register saved?
   unsigned long used_reg_bits = fnbe->ra->used_reg_bits;
+  int vaarg_params_saved = 0;
   if (!no_stmt) {
+    if (func->type->func.vaargs) {
+      vaarg_params_saved = put_vaarg_params(func);
+
+      // Re-align frame size.
+      frame_size = ALIGN(fnbe->frame_size + vaarg_params_saved, 16) - vaarg_params_saved;
+    }
+
     fp_saved = frame_size > 0 || fnbe->ra->flag & RAF_STACK_FRAME;
     ra_saved = (func->flag & FUNCF_HAS_FUNCALL) != 0;
 
@@ -542,6 +559,8 @@ static void emit_defun(Function *func) {
         ADD(SP, SP, IM(16));
       }
     }
+    if (vaarg_params_saved > 0)
+      ADD(SP, SP, IM(vaarg_params_saved));
 
     RET();
   }

src/cc/backend/codegen.c

@@ -777,8 +777,13 @@ void alloc_stack_variables_onto_stack_frame(Function *func) {
   int param_offset = calculate_func_param_bottom(func);
   fnbe->vaarg_frame_info.offset = param_offset;
 
-  if (func->type->func.vaargs)
+  if (func->type->func.vaargs) {
+#if VAARG_FP_AS_GP
+    // Register parameters are put below stack frame, so not added to frame_size.
+#else
     frame_size = (MAX_REG_ARGS + MAX_FREG_ARGS) * POINTER_SIZE;
+#endif
+  }
 
   bool require_stack_frame = false;
 

src/cc/builtin.c

@@ -48,6 +48,46 @@ static VReg *gen_builtin_va_start(Expr *expr) {
   new_ir_mov(varinfo->local.vreg, ptr, IRF_UNSIGNED);
   return NULL;
 }
+#elif XCC_TARGET_ARCH == XCC_ARCH_RISCV64
+static VReg *gen_builtin_va_start(Expr *expr) {
+  assert(expr->kind == EX_FUNCALL);
+  Vector *args = expr->funcall.args;
+  assert(args->len == 2);
+  assert(curfunc != NULL);
+  Expr *var = strip_cast(args->data[1]);
+  if (var->kind == EX_REF)
+    var = var->unary.sub;
+  int gn = -1;
+  if (var->kind == EX_VAR) {
+    const Vector *params = curfunc->params;
+    int g = 0;
+    for (int i = 0; i < params->len; ++i) {
+      VarInfo *info = params->data[i];
+      const Type *t = info->type;
+      if (t->kind != TY_STRUCT) {
+        ++g;
+      }
+
+      if (info->name != NULL && equal_name(info->name, var->var.name)) {
+        gn = g;
+        break;
+      }
+    }
+  }
+  if (gn < 0) {
+    parse_error(PE_FATAL, var->token, "Must be function argument");
+    return NULL;
+  }
+
+  FuncBackend *fnbe = curfunc->extra;
+  FrameInfo *fi = &fnbe->vaarg_frame_info;
+  VReg *p = new_ir_bofs(fi);
+
+  // (void)(ap = fp + <vaarg saved offset>)
+  VReg *ap = gen_expr(args->data[0]);
+  new_ir_mov(ap, p, IRF_UNSIGNED);
+  return NULL;
+}
 #else
 static VReg *gen_builtin_va_start(Expr *expr) {
   assert(expr->kind == EX_FUNCALL);
@@ -146,7 +186,7 @@ void install_builtins(void) {
   add_builtin_expr_ident("__builtin_type_kind", &p_reg_class);
 
   {
-#if VAARG_ON_STACK
+#if VAARG_ON_STACK || XCC_TARGET_ARCH == XCC_ARCH_RISCV64
     Type *tyVaList = ptrof(&tyVoidPtr);
 #else
     Type *tyVaElem = create_struct_type(NULL, alloc_name("__va_elem", NULL, false), 0);