qom: Allow objects to be allocated with increased alignment

It turns out that some hosts have a default malloc alignment less
than that required for vectors.

We assume that, with compiler annotation on CPUArchState, that we
can properly align the vector portion of the guest state.  Fix the
alignment of the allocation by using qemu_memalloc when required.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200916004638.2444147-3-richard.henderson@linaro.org>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

2 files changed, 38 insertions, 3 deletions

diff --git a/include/qom/object.h b/include/qom/object.h
index 32524d72cc..405a2c67b0 100644
--- a/include/qom/object.h
+++ b/include/qom/object.h
@@ -691,6 +691,7 @@ struct Object
         .parent = TYPE_##PARENT_MODULE_OBJ_NAME, \
         .name = TYPE_##MODULE_OBJ_NAME, \
         .instance_size = sizeof(ModuleObjName), \
+        .instance_align = __alignof__(ModuleObjName), \
         .instance_init = module_obj_name##_init, \
         .instance_finalize = module_obj_name##_finalize, \
         .class_size = sizeof(ModuleObjName##Class), \
@@ -770,6 +771,9 @@ struct Object
  * @instance_size: The size of the object (derivative of #Object).  If
  *   @instance_size is 0, then the size of the object will be the size of the
  *   parent object.
+ * @instance_align: The required alignment of the object.  If @instance_align
+ *   is 0, then normal malloc alignment is sufficient; if non-zero, then we
+ *   must use qemu_memalign for allocation.
  * @instance_init: This function is called to initialize an object.  The parent
  *   class will have already been initialized so the type is only responsible
  *   for initializing its own members.
@@ -807,6 +811,7 @@ struct TypeInfo
     const char *parent;
 
     size_t instance_size;
+    size_t instance_align;
     void (*instance_init)(Object *obj);
     void (*instance_post_init)(Object *obj);
     void (*instance_finalize)(Object *obj);
diff --git a/qom/object.c b/qom/object.c
index cecad35b99..a91a6a515a 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -50,6 +50,7 @@ struct TypeImpl
     size_t class_size;
 
     size_t instance_size;
+    size_t instance_align;
 
     void (*class_init)(ObjectClass *klass, void *data);
     void (*class_base_init)(ObjectClass *klass, void *data);
@@ -114,6 +115,7 @@ static TypeImpl *type_new(const TypeInfo *info)
 
     ti->class_size = info->class_size;
     ti->instance_size = info->instance_size;
+    ti->instance_align = info->instance_align;
 
     ti->class_init = info->class_init;
     ti->class_base_init = info->class_base_init;
@@ -688,16 +690,44 @@ static void object_finalize(void *data)
     }
 }
 
+/* Find the minimum alignment guaranteed by the system malloc. */
+#if __STDC_VERSION__ >= 201112L
+typddef max_align_t qemu_max_align_t;
+#else
+typedef union {
+    long l;
+    void *p;
+    double d;
+    long double ld;
+} qemu_max_align_t;
+#endif
+
 static Object *object_new_with_type(Type type)
 {
     Object *obj;
+    size_t size, align;
+    void (*obj_free)(void *);
 
     g_assert(type != NULL);
     type_initialize(type);
 
-    obj = g_malloc(type->instance_size);
-    object_initialize_with_type(obj, type->instance_size, type);
-    obj->free = g_free;
+    size = type->instance_size;
+    align = type->instance_align;
+
+    /*
+     * Do not use qemu_memalign unless required.  Depending on the
+     * implementation, extra alignment implies extra overhead.
+     */
+    if (likely(align <= __alignof__(qemu_max_align_t))) {
+        obj = g_malloc(size);
+        obj_free = g_free;
+    } else {
+        obj = qemu_memalign(align, size);
+        obj_free = qemu_vfree;
+    }
+
+    object_initialize_with_type(obj, size, type);
+    obj->free = obj_free;
 
     return obj;
 }