From 320ee19b61260a4774759fb3dcb6e04154d53dab Mon Sep 17 00:00:00 2001
From: slava <slava@factorcode.org>
Date: Mon, 4 Dec 2006 05:20:54 +0000
Subject: [PATCH] Fix bug in code GC free list handling

---
 vm/code_gc.c | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/vm/code_gc.c b/vm/code_gc.c
index 56853faee3..b1205c0dea 100644
--- a/vm/code_gc.c
+++ b/vm/code_gc.c
@@ -28,12 +28,14 @@ INLINE void update_free_list(F_HEAP *heap, F_BLOCK *prev, F_BLOCK *next_free)
 		heap->free_list = next_free;
 }
 
-/* Called after reading the code heap from the image file. We must build the
-free list, and add a large free block from compiling.base + size to
+/* Called after reading the code heap from the image file, and after code GC.
+
+In the former case, we must add a large free block from compiling.base + size to
 compiling.limit. */
 void build_free_list(F_HEAP *heap, CELL size)
 {
 	F_BLOCK *prev = NULL;
+	F_BLOCK *prev_free = NULL;
 	F_BLOCK *scan = (F_BLOCK *)heap->base;
 	F_BLOCK *end = (F_BLOCK *)(heap->base + size);
 
@@ -42,29 +44,39 @@ void build_free_list(F_HEAP *heap, CELL size)
 	{
 		if(scan->status == B_FREE)
 		{
-			update_free_list(heap,prev,scan);
-			prev = scan;
+			update_free_list(heap,prev_free,scan);
+			prev_free = scan;
 		}
 
+		prev = scan;
 		scan = next_block(heap,scan);
 	}
 
-	/* If there is room at the end of the heap, add a free block */
+	/* If there is room at the end of the heap, add a free block. This
+	branch is only taken after loading a new image, not after code GC */
 	if((CELL)(end + 1) <= heap->limit)
 	{
 		end->status = B_FREE;
 		end->next_free = NULL;
 		end->size = heap->limit - (CELL)end;
+
+		/* add final free block */
+		update_free_list(heap,prev_free,end);
 	}
+	/* This branch is taken if the newly loaded image fits exactly, or
+	after code GC */
 	else
 	{
-		end = NULL;
-
+		/* even if there's no room at the end of the heap for a new
+		free block, we might have to jigger it up by a few bytes in
+		case prev + prev->size */
 		if(prev)
 			prev->size = heap->limit - (CELL)prev;
+
+		/* this is the last free block */
+		update_free_list(heap,prev_free,NULL);
 	}
 
-	update_free_list(heap,prev,end);
 }
 
 /* Allocate a block of memory from the mark and sweep GC heap */