From 0d0f89ad33b8b68d7fe4502292ebb41879f26096 Mon Sep 17 00:00:00 2001
From: Nunuhara Cabbage <nunuhara@haniwa.technology>
Date: Sun, 8 Dec 2019 11:42:51 -0800
Subject: [PATCH] Track free address for HEAP_DEBUG

Useful for debugging double free errors.
---
 vm.c | 11 +++++++++--
 vm.h |  1 +
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/vm.c b/vm.c
index 1fcd82a..d81622d 100644
--- a/vm.c
+++ b/vm.c
@@ -151,9 +151,16 @@ static const char *vm_ptrtype_string(enum vm_pointer_type type) {
 void heap_unref(int slot)
 {
 	if (heap[slot].ref <= 0) {
+#ifdef DEBUG_HEAP
+		VM_ERROR("double free of slot %d (%s)\nOriginally allocd at %X\nOriginally freed at %X",
+			 slot, vm_ptrtype_string(heap[slot].type), heap[slot].alloc_addr, heap[slot].free_addr);
+#endif
 		VM_ERROR("double free of slot %d (%s)", slot, vm_ptrtype_string(heap[slot].type));
 	}
 	if (--heap[slot].ref <= 0) {
+#ifdef DEBUG_HEAP
+		heap[slot].free_addr = instr_ptr;
+#endif
 		switch (heap[slot].type) {
 		case VM_PAGE:
 			if (heap[slot].page) {
@@ -447,9 +454,9 @@ static void hll_call(int libno, int fno)
 
 static void function_return(void)
 {
+	heap_unref(call_stack[call_stack_ptr-1].page_slot);
+	instr_ptr = call_stack[call_stack_ptr-1].return_address;
 	call_stack_ptr--;
-	heap_unref(call_stack[call_stack_ptr].page_slot);
-	instr_ptr = call_stack[call_stack_ptr].return_address;
 }
 
 static void system_call(int32_t code)
diff --git a/vm.h b/vm.h
index 6436f3e..59e1469 100644
--- a/vm.h
+++ b/vm.h
@@ -54,6 +54,7 @@ struct vm_pointer {
 #ifdef DEBUG_HEAP
 	size_t alloc_addr;
 	size_t ref_addr;
+	size_t free_addr;
 #endif
 };