From e8f5fa88b59afe9be99a2b03e65293e0bcbb924b Mon Sep 17 00:00:00 2001
From: Andrew Scott <git@andyscott.me>
Date: Wed, 18 Sep 2024 17:22:21 -0400
Subject: [PATCH] malloc: added `destroy_heap` function

---
 include/gc_malloc.h | 11 +++++++----
 src/gc_malloc.c     | 34 ++++++++++++++++++++++++++++++++--
 2 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/include/gc_malloc.h b/include/gc_malloc.h
index b3c97b0..d6660f4 100644
--- a/include/gc_malloc.h
+++ b/include/gc_malloc.h
@@ -45,13 +45,13 @@ struct gc_chunk *find_prev_chunk(struct gc_chunk *curr);
 void set_footer(struct gc_chunk *curr);
 
 // Gets footer information for the current chunk - useful for debugging
-int get_footer(struct gc_chunk *curr);
+uint64_t get_footer(struct gc_chunk *curr);
 
 // Creates a new chunk with sentinel
 struct gc_chunk *init_gc_chunk(void);
 
-// Gets a pointer to a suitable chunk from the free list, otherwise creates a
-// new chunk and returns it's pointer
+// Gets a pointer to a suitable chunk (first fit) from the free list, otherwise
+// creates a new chunk and returns it's pointer
 struct gc_chunk *find_free_chunk(size_t size);
 
 // Coalesces chunks when merge flag is set
@@ -60,7 +60,10 @@ void merge_chunk(struct gc_chunk *curr);
 // Performs allocations of SIZE bytes
 void *gc_malloc(size_t size);
 
-// Frees blocks of memory allocated by 'gc_alloc'
+// Frees allocations for re-use
 void gc_free(void *ptr);
 
+// Completely de-allocates the heap (break glass in case of emergency)
+void destroy_heap(struct gc_chunk *freelist);
+
 #endif /* GC_MALLOC_H */
diff --git a/src/gc_malloc.c b/src/gc_malloc.c
index 1f27382..8efb5b2 100644
--- a/src/gc_malloc.c
+++ b/src/gc_malloc.c
@@ -1,12 +1,18 @@
 #include <assert.h>
 #include <stdint.h>
+#include <stdio.h>
 #include <sys/mman.h>
 #include <unistd.h>
 
 #include "gc_malloc.h"
 
+/* Static Variables */
+
+// Doubly linked list to keep track of free chunks
 static struct gc_chunk *freelist = NULL;
 
+/* Static Inline Functions */
+
 // Hides chunk header
 static inline void *hide(struct gc_chunk *curr)
 {
@@ -43,6 +49,8 @@ static inline uint32_t align(uint32_t size)
 		return size;
 }
 
+/* Debug Functions */
+
 // Useful for debugging after find or merge are called
 static void chk_freelist(void)
 {
@@ -63,6 +71,8 @@ static void chk_freelist(void)
 	}
 }
 
+/* gc_malloc Functions */
+
 struct gc_chunk *find_next_chunk(struct gc_chunk *curr)
 {
 	unsigned size = curr->size;
@@ -82,7 +92,7 @@ void set_footer(struct gc_chunk *curr)
 	next->footer = curr->size;
 }
 
-int get_footer(struct gc_chunk *curr)
+uint64_t get_footer(struct gc_chunk *curr)
 {
 	struct gc_chunk *next = find_next_chunk(curr);
 	return next->footer;
@@ -119,8 +129,12 @@ struct gc_chunk *init_gc_chunk(void)
 struct gc_chunk *find_free_chunk(size_t size)
 {
 	// HACK: The first loop will run forever if we can never get a big enough chunk
-	if (size > getpagesize())
+	const size_t page = getpagesize();
+	if (size > page) {
+		fprintf(stderr,
+			"ERROR: find_free_chunk: Requested size is larger than a page!");
 		return NULL;
+	}
 
 	struct gc_chunk *found;
 
@@ -151,6 +165,7 @@ struct gc_chunk *find_free_chunk(size_t size)
 	return found;
 }
 
+// FIXME: need to clean up todos before this will work
 void merge_chunk(struct gc_chunk *curr)
 {
 	if (curr->merge) {
@@ -201,3 +216,18 @@ void gc_free(void *ptr)
 		chk_freelist(); // TODO: Remove this line after debugging
 	}
 }
+
+void destroy_heap(struct gc_chunk *freelist)
+{
+	if (freelist == NULL) {
+		fprintf(stderr, "WARN: destroy_heap: Free list is empty?");
+		return;
+	}
+
+	struct gc_chunk *curr = freelist;
+	while (curr->size != 0) {
+		struct gc_chunk *next = curr->next;
+		munmap(curr, curr->size);
+		curr = curr->next;
+	}
+}