VGA Z-buffer is now dynamically allocated and freed

memory management can reuse the last pointer malloced if freed again

3 files changed, 21 insertions, 8 deletions

diff --git a/src/kernel/kernel.c b/src/kernel/kernel.c
index f2210d6..c0bc285 100644
--- a/src/kernel/kernel.c
+++ b/src/kernel/kernel.c
@@ -91,13 +91,14 @@ void kernel_main( void )
 	// TODO: get memupper from multiboot header (but this needs
 	// a multiboot compliant entry function first) or use BIOS
 	// functions to determine size of memory, for now assume we
-	// have at least, for now use the memory above 1 MB, 64 MB
-	// heap is enough for what we are doing in the kernel
-	memory_manager_init( &global_context.memory_manager, 0x100000, 0xFFFF );
+	// have at least, for now use the memory above 1 MB, 128 KB
+	// heap is enough for what we are doing in the kernel plus
+	// eventual z buffering the VGA graphic mode
+	uint32_t heap_offset = 0x01000000;
+	size_t heap_size = 128 * 1024;
+	memory_manager_init( &global_context.memory_manager, heap_offset, heap_size );
 	__stdlib_set_memory_manager( &global_context.memory_manager );
-	printf( "Kernel heap at 0x%X, size 0x%X\n", 0x100000, 0xFFFF );
-	void *test = malloc( 2048 );
-	free( test );
+	printf( "Kernel heap at 0x%X, size 0x%X\n", heap_offset, heap_size );
 
 	// exit point in case of kernel panic, do this as soon as
 	// possible, as soon we have an early console we can croak on
diff --git a/src/kernel/memorymanagement.c b/src/kernel/memorymanagement.c
index dc2d160..b8a84b2 100644
--- a/src/kernel/memorymanagement.c
+++ b/src/kernel/memorymanagement.c
@@ -11,6 +11,7 @@ void memory_manager_init( memory_manager_t *memory_manager, size_t offset, size_
 	memory_manager->offset = offset;
 	memory_manager->size = size;
 	memory_manager->free_ptr = offset;
+	memory_manager->prev_ptr = 0xFFFFFFFF;
 }
 
 void *memory_manager_allocate( memory_manager_t *memory_manager, size_t size )
@@ -19,10 +20,11 @@ void *memory_manager_allocate( memory_manager_t *memory_manager, size_t size )
 
 	if( memory_manager->free_ptr - memory_manager->offset + size > memory_manager->size ) {
 		kernel_panic( "Heap allocation out of memory (requested %d bytes, available %d)",
-			size, size - ( memory_manager->free_ptr - memory_manager->offset ) - 1 );
+			size, size - ( memory_manager->free_ptr - memory_manager->offset ) );
 	}
 
 	p = (void *)memory_manager->free_ptr;
+	memory_manager->prev_ptr = memory_manager->free_ptr;
 	memory_manager->free_ptr += size;
 
 	return p;
@@ -34,7 +36,16 @@ void memory_manager_deallocate( memory_manager_t *memory_manager, void **p )
 		kernel_panic( "Double free of pointer 0x%X in heap", *p );
 	}
 
-	*p = NULL;
+	// This actually doesn't work and we do it outside after free, when
+	// a buffer has an optional semantic
+	//*p = NULL;
+	
+	// are we freeing the previously allocated block, if yes, we can
+	// adjust the free pointer
+	if( (uint32_t)*p == memory_manager->prev_ptr ) {
+		memory_manager->free_ptr = memory_manager->prev_ptr;
+		memory_manager->prev_ptr = 0xFFFFFFFF;
+	}
 }
 
 
diff --git a/src/kernel/memorymanagement.h b/src/kernel/memorymanagement.h
index 16f0b29..647c05d 100644
--- a/src/kernel/memorymanagement.h
+++ b/src/kernel/memorymanagement.h
@@ -6,6 +6,7 @@
 typedef struct {
 	size_t offset;
 	size_t size;
+	uint32_t prev_ptr;
 	uint32_t free_ptr;
 } memory_manager_t;