malloc_debug: Add default alignment option.

This allows for something similar as was implemented in 217f090 but
makes it optional and configurable.

The MALLOC_DEBUG environment variable now can take "a<size>" to set
the default alignment to the specified size. Note that not all
alignments may be supported depending on the heap implementation.

headers/posix/malloc_debug.h

@@ -18,6 +18,7 @@ status_t heap_debug_stop_wall_checking();
 void heap_debug_set_memory_reuse(bool enabled);
 void heap_debug_set_paranoid_validation(bool enabled);
 void heap_debug_set_debugger_calls(bool enabled);
+void heap_debug_set_default_alignment(size_t defaultAlignment);
 void heap_debug_validate_heaps();
 void heap_debug_validate_walls();
 

src/system/libroot/posix/malloc_debug/guarded_heap.cpp

@@ -19,6 +19,7 @@
 
 
 static bool sDebuggerCalls = true;
+static size_t sDefaultAlignment = 0;
 
 
 static void
@@ -833,6 +834,13 @@ heap_debug_set_debugger_calls(bool enabled)
 }
 
 
+extern "C" void
+heap_debug_set_default_alignment(size_t defaultAlignment)
+{
+	sDefaultAlignment = defaultAlignment;
+}
+
+
 extern "C" void
 heap_debug_validate_heaps()
 {
@@ -937,6 +945,14 @@ __init_heap_post_env(void)
 	if (mode != NULL) {
 		if (strchr(mode, 'r'))
 			heap_debug_set_memory_reuse(false);
+
+		size_t defaultAlignment = 0;
+		const char *argument = strchr(mode, 'a');
+		if (argument != NULL
+			&& sscanf(argument, "a%" B_SCNuSIZE, &defaultAlignment) == 1
+			&& defaultAlignment > 0) {
+			heap_debug_set_default_alignment(defaultAlignment);
+		}
 	}
 }
 
@@ -966,7 +982,7 @@ memalign(size_t alignment, size_t size)
 extern "C" void*
 malloc(size_t size)
 {
-	return memalign(0, size);
+	return memalign(sDefaultAlignment, size);
 }
 
 
@@ -987,7 +1003,7 @@ realloc(void* address, size_t newSize)
 	}
 
 	if (address == NULL)
-		return memalign(0, newSize);
+		return memalign(sDefaultAlignment, newSize);
 
 	return guarded_heap_realloc(address, newSize);
 }

src/system/libroot/posix/malloc_debug/heap.cpp

@@ -44,6 +44,7 @@ static bool sParanoidValidation = false;
 static thread_id sWallCheckThread = -1;
 static bool sStopWallChecking = false;
 static bool sUseGuardPage = false;
+static bool sDefaultAlignment = 0;
 
 
 void
@@ -1465,7 +1466,7 @@ heap_realloc(heap_allocator *heap, void *address, void **newAddress,
 	newSize -= sizeof(addr_t) + sizeof(heap_leak_check_info);
 
 	// if not, allocate a new chunk of memory
-	*newAddress = memalign(0, newSize);
+	*newAddress = memalign(sDefaultAlignment, newSize);
 	if (*newAddress == NULL) {
 		// we tried but it didn't work out, but still the operation is done
 		return B_OK;
@@ -1681,6 +1682,13 @@ heap_debug_set_debugger_calls(bool enabled)
 }
 
 
+extern "C" void
+heap_debug_set_default_alignment(size_t defaultAlignment)
+{
+	sDefaultAlignment = defaultAlignment;
+}
+
+
 extern "C" void
 heap_debug_validate_heaps()
 {
@@ -1839,6 +1847,14 @@ __init_heap_post_env(void)
 			sUseGuardPage = true;
 		if (strchr(mode, 'r'))
 			heap_debug_set_memory_reuse(false);
+
+		size_t defaultAlignment = 0;
+		const char *argument = strchr(mode, 'a');
+		if (argument != NULL
+			&& sscanf(argument, "a%" B_SCNuSIZE, &defaultAlignment) == 1
+			&& defaultAlignment > 0) {
+			heap_debug_set_default_alignment(defaultAlignment);
+		}
 	}
 }
 
@@ -1937,7 +1953,7 @@ malloc(size_t size)
 	if (sUseGuardPage)
 		return heap_debug_malloc_with_guard_page(size);
 
-	return memalign(0, size);
+	return memalign(sDefaultAlignment, size);
 }
 
 
@@ -1978,7 +1994,7 @@ void *
 realloc(void *address, size_t newSize)
 {
 	if (address == NULL)
-		return memalign(0, newSize);
+		return memalign(sDefaultAlignment, newSize);
 
 	if (newSize == 0) {
 		free(address);