From 8f0fa8d70ce08ee0347a5880d44faab8307b72f6 Mon Sep 17 00:00:00 2001
From: nsfisis <nsfisis@gmail.com>
Date: Sat, 10 Jan 2026 00:33:08 +0900
Subject: feat: implement va_arg()

---
 src/codegen.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 src/parse.c   | 10 +++++++---
 2 files changed, 49 insertions(+), 3 deletions(-)

(limited to 'src')

diff --git a/src/codegen.c b/src/codegen.c
index 7adff5a..1c7abf7 100644
--- a/src/codegen.c
+++ b/src/codegen.c
@@ -447,6 +447,48 @@ static void codegen_func_call(CodeGen* g, AstNode* ast) {
         return;
     }
 
+    if (strcmp(func_name, "__ducc_va_arg") == 0) {
+        fprintf(g->out, "  # __ducc_va_arg BEGIN\n");
+
+        // Evaluate va_list argument (first argument)
+        AstNode* va_list_arg = &ast->node_args->node_items[0];
+        codegen_expr(g, va_list_arg, GenMode_rval);
+        fprintf(g->out, "  pop rdi\n"); // rdi = pointer to va_list
+
+        // Evaluate size argument (second argument)
+        AstNode* size_arg = &ast->node_args->node_items[1];
+        codegen_expr(g, size_arg, GenMode_rval);
+        fprintf(g->out, "  pop rsi\n"); // rsi = size
+
+        int label = codegen_new_label(g);
+
+        // Check if gp_offset < 48 (6 registers * 8 bytes)
+        fprintf(g->out, "  mov eax, DWORD PTR [rdi]\n"); // eax = gp_offset
+        fprintf(g->out, "  cmp eax, 48\n");
+        fprintf(g->out, "  jae .Lva_arg_overflow%d\n", label);
+
+        // Fetch from register save area
+        fprintf(g->out, "  mov rcx, QWORD PTR [rdi+16]\n"); // rcx = reg_save_area
+        fprintf(g->out, "  movsx rdx, eax\n");              // rdx = gp_offset (sign-extended)
+        fprintf(g->out, "  add rcx, rdx\n");                // rcx = reg_save_area + gp_offset
+        fprintf(g->out, "  add eax, 8\n");                  // gp_offset += 8
+        fprintf(g->out, "  mov DWORD PTR [rdi], eax\n");    // store updated gp_offset
+        fprintf(g->out, "  mov rax, rcx\n");                // return pointer to argument
+        fprintf(g->out, "  jmp .Lva_arg_end%d\n", label);
+
+        // Fetch from overflow area (stack)
+        fprintf(g->out, ".Lva_arg_overflow%d:\n", label);
+        fprintf(g->out, "  mov rcx, QWORD PTR [rdi+8]\n"); // rcx = overflow_arg_area
+        fprintf(g->out, "  mov rax, rcx\n");               // return pointer to argument
+        fprintf(g->out, "  add rcx, 8\n");                 // overflow_arg_area += 8
+        fprintf(g->out, "  mov QWORD PTR [rdi+8], rcx\n"); // store updated overflow_arg_area
+
+        fprintf(g->out, ".Lva_arg_end%d:\n", label);
+        fprintf(g->out, "  push rax\n");
+        fprintf(g->out, "  # __ducc_va_arg END\n");
+        return;
+    }
+
     AstNode* args = ast->node_args;
 
     int gp_regs = 6;
diff --git a/src/parse.c b/src/parse.c
index b201aaf..c602073 100644
--- a/src/parse.c
+++ b/src/parse.c
@@ -165,8 +165,11 @@ static Parser* parser_new(TokenArray* tokens) {
 
     Func* va_start_func = funcs_push_new(&p->funcs);
     va_start_func->name = "__ducc_va_start";
-    va_start_func->ty = calloc(1, sizeof(Type));
-    va_start_func->ty->kind = TypeKind_void;
+    va_start_func->ty = type_new_func(type_new(TypeKind_void), NULL);
+
+    Func* va_arg_func = funcs_push_new(&p->funcs);
+    va_arg_func->name = "__ducc_va_arg";
+    va_arg_func->ty = type_new_func(type_new_ptr(type_new(TypeKind_void)), NULL);
 
     return p;
 }
@@ -524,6 +527,7 @@ static bool is_type_token(Parser* p, Token* tok) {
 }
 
 static Type* parse_type_name(Parser* p);
+static AstNode* parse_cast_expr(Parser* p);
 
 static AstNode* parse_prefix_expr(Parser* p) {
     TokenKind op = peek_token(p)->kind;
@@ -540,7 +544,7 @@ static AstNode* parse_prefix_expr(Parser* p) {
         AstNode* operand = parse_prefix_expr(p);
         return ast_new_ref_expr(operand);
     } else if (consume_token_if(p, TokenKind_star)) {
-        AstNode* operand = parse_prefix_expr(p);
+        AstNode* operand = parse_cast_expr(p);
         return ast_new_deref_expr(operand);
     } else if (consume_token_if(p, TokenKind_plusplus)) {
         AstNode* operand = parse_prefix_expr(p);
-- 
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