Tidied up init_heap()

src/core/heap.c

@@ -8,88 +8,75 @@ struct heap_block {
 	char data[0];
 };
 
-size_t heap_ptr, heap_top, heap_bot;
+/* Linker symbols */
+extern char _text[];
+extern char _end[];
 
-#define _virt_start 0
+static unsigned long heap_start, heap_end, heap_ptr;
+
+/*
+ * Find the largest contiguous area of memory that I can use for the
+ * heap.
+ *
+ */
+static void init_heap ( void ) {
+	unsigned int i;
+	unsigned long eb_start, eb_end;
+	unsigned long size;
 
-static void init_heap(void)
-{
-	size_t size;
-	size_t start, end;
-	unsigned i;
-	/* Find the largest contiguous area of memory that
-	 * I can use for the heap, which is organized as 
-	 * a stack that grows backwards through memory.
-	 */
-
-	/* If I have virtual address that do not equal physical addresses
-	 * there is a change I will try to use memory from both sides of
-	 * the virtual address space simultaneously, which can cause all kinds
-	 * of interesting problems.
-	 * Avoid it by logically extending etherboot.  Once I know that relocation
-	 * works I can just start the virtual address space at 0, and this problem goes
-	 * away so that is probably a better solution.
-	 */
-#if 0
-	start = virt_to_phys(_text);
-#else
-	/* segment wrap around is nasty don't chance it. */
-	start = virt_to_phys(_virt_start);
-#endif
-	end  = virt_to_phys(_end);
 	size = 0;
-	for(i = 0; i < meminfo.map_count; i++) {
-		unsigned long r_start, r_end;
-		if (meminfo.map[i].type != E820_RAM)
-			continue;
-		if (meminfo.map[i].addr > ULONG_MAX)
+	
+	/* Region occupied by Etherboot */
+	eb_start = virt_to_phys ( _text );
+	eb_end = virt_to_phys ( _end );
+
+	for ( i = 0 ; i < meminfo.map_count ; i++ ) {
+		unsigned long r_start, r_end, r_size;
+		unsigned long pre_eb, post_eb;
+
+		/* Get start and end addresses of the region */
+		if ( meminfo.map[i].type != E820_RAM )
 			continue;
-		if (meminfo.map[i].size > ULONG_MAX)
+		if ( meminfo.map[i].addr > ULONG_MAX )
 			continue;
-		
 		r_start = meminfo.map[i].addr;
-		r_end = r_start + meminfo.map[i].size;
-		if (r_end < r_start) {
+		if ( r_start + meminfo.map[i].size > ULONG_MAX ) {
 			r_end = ULONG_MAX;
+		} else {
+			r_end = r_start + meminfo.map[i].size;
 		}
-		/* Handle areas that overlap etherboot */
-		if ((end > r_start) && (start < r_end)) {
-			/* Etherboot completely covers the region */
-			if ((start <= r_start) && (end >= r_end))
-				continue;
-			/* Etherboot is completely contained in the region */
-			if ((start > r_start) && (end < r_end)) {
-				/* keep the larger piece */
-				if ((r_end - end) >= (r_start - start)) {
-					r_start = end;
-				}
-				else {
-					r_end = start;
-				}
-			}
-			/* Etherboot covers one end of the region.
-			 * Shrink the region.
-			 */
-			else if (end >= r_end) {
-				r_end = start;
-			}
-			else if (start <= r_start) {
-				r_start = end;
+		
+		/* Avoid overlap with Etherboot.  When Etherboot is
+		 * completely contained within the region, choose the
+		 * larger of the two remaining portions.
+		 */
+		if ( ( eb_start < r_end ) && ( eb_end > r_start ) ) {
+			pre_eb = ( eb_start > r_start ) ?
+				( eb_start - r_start ) : 0;
+			post_eb = ( r_end > eb_end ) ?
+				( r_end - eb_end ) : 0;
+			if ( pre_eb > post_eb ) {
+				r_end = eb_start;
+			} else {
+				r_start = eb_end;
 			}
 		}
-		/* If two areas are the size prefer the greater address */
-		if (((r_end - r_start) > size) ||
-			(((r_end - r_start) == size) && (r_start > heap_top))) {
-			size = r_end - r_start;
-			heap_top = r_start;
-			heap_bot = r_end;
+
+		/* Use the biggest region.  Where two regions are the
+		 * same size, use the later region.  (Provided that
+		 * the memory map is laid out in a sensible order,
+		 * this should give us the higher region.)
+		 */
+		r_size = r_end - r_start;
+		if ( r_size >= size ) {
+			heap_start = r_start;
+			heap_end = r_end;
+			size = r_size;
 		}
 	}
-	if (size == 0) {
-		printf("init_heap: No heap found.\n");
-		exit(1);
-	}
-	heap_ptr = heap_bot;
+
+	ASSERT ( size != 0 );
+	heap_ptr = heap_end;
 }
 
 /*
@@ -104,7 +91,7 @@ void * emalloc ( size_t size, unsigned int align ) {
 	
 	addr = ( ( ( heap_ptr - size ) & ~( align - 1 ) )
 		 - sizeof ( struct heap_block ) );
-	if ( addr < heap_top ) {
+	if ( addr < heap_start ) {
 		return NULL;
 	}
 
@@ -119,7 +106,7 @@ void * emalloc ( size_t size, unsigned int align ) {
  *
  */
 void * emalloc_all ( size_t *size ) {
-	*size = heap_ptr - heap_top - sizeof ( struct heap_block );
+	*size = heap_ptr - heap_start - sizeof ( struct heap_block );
 	return emalloc ( *size, sizeof ( void * ) );
 }
 
@@ -136,7 +123,7 @@ void efree ( void *ptr ) {
 		( ptr - offsetof ( struct heap_block, data ) );
 	heap_ptr += block->size;
 
-	ASSERT ( heap_ptr <= heap_bot );
+	ASSERT ( heap_ptr <= heap_end );
 }
 
 /*
@@ -144,7 +131,7 @@ void efree ( void *ptr ) {
  *
  */
 void efree_all ( void ) {
-	heap_ptr = heap_bot;
+	heap_ptr = heap_end;
 }
 
 INIT_FN ( INIT_HEAP, init_heap, efree_all, NULL );