[arm64] Remove the limitation on the number of nullable arguments for…

… dyncalls.

Fixes xamarin/xamarin-macios#4984.

mono/mini/mini-arm64.c

@@ -1581,7 +1581,7 @@ typedef struct {
 	CallInfo *cinfo;
 	MonoType *rtype;
 	MonoType **param_types;
-	int n_fpargs, n_fpret;
+	int n_fpargs, n_fpret, nullable_area;
 } ArchDynCallInfo;
 
 static gboolean
@@ -1634,7 +1634,7 @@ mono_arch_dyn_call_prepare (MonoMethodSignature *sig)
 {
 	ArchDynCallInfo *info;
 	CallInfo *cinfo;
-	int i;
+	int i, aindex;
 
 	cinfo = get_call_info (NULL, sig);
 
@@ -1663,6 +1663,28 @@ mono_arch_dyn_call_prepare (MonoMethodSignature *sig)
 	default:
 		break;
 	}
+
+	for (aindex = 0; aindex < sig->param_count; aindex++) {
+		MonoType *t = info->param_types [aindex];
+
+		if (t->byref)
+			continue;
+
+		switch (t->type) {
+		case MONO_TYPE_GENERICINST:
+			if (t->type == MONO_TYPE_GENERICINST && mono_class_is_nullable (mono_class_from_mono_type_internal (t))) {
+				MonoClass *klass = mono_class_from_mono_type_internal (t);
+				int size;
+
+				/* Nullables need a temporary buffer, its stored at the end of DynCallArgs.regs after the stack args */
+				size = mono_class_value_size (klass, NULL);
+				info->nullable_area += size;
+			}
+			break;
+		default:
+			break;
+		}
+	}
 
 	return (MonoDynCallInfo*)info;
 }
@@ -1683,7 +1705,7 @@ mono_arch_dyn_call_get_buf_size (MonoDynCallInfo *info)
 	ArchDynCallInfo *ainfo = (ArchDynCallInfo*)info;
 
 	g_assert (ainfo->cinfo->stack_usage % MONO_ARCH_FRAME_ALIGNMENT == 0);
-	return sizeof (DynCallArgs) + ainfo->cinfo->stack_usage;
+	return sizeof (DynCallArgs) + ainfo->cinfo->stack_usage + ainfo->nullable_area;
 }
 
 static double
@@ -1711,6 +1733,7 @@ mono_arch_start_dyn_call (MonoDynCallInfo *info, gpointer **args, guint8 *ret, g
 	MonoMethodSignature *sig = dinfo->sig;
 	CallInfo *cinfo = dinfo->cinfo;
 	int buffer_offset = 0;
+	guint8 *nullable_buffer;
 
 	p->res = 0;
 	p->ret = ret;
@@ -1722,6 +1745,9 @@ mono_arch_start_dyn_call (MonoDynCallInfo *info, gpointer **args, guint8 *ret, g
 	greg = 0;
 	pindex = 0;
 
+	/* Stored after the stack arguments */
+	nullable_buffer = (guint8*)&(p->regs [PARAM_REGS + 1 + (cinfo->stack_usage / sizeof (mgreg_t))]);
+
 	if (sig->hasthis)
 		p->regs [greg ++] = (mgreg_t)*(args [arg_index ++]);
 
@@ -1827,9 +1853,9 @@ mono_arch_start_dyn_call (MonoDynCallInfo *info, gpointer **args, guint8 *ret, g
 					 * if the nullable param is passed by ref.
 					 */
 					size = mono_class_value_size (klass, NULL);
-					nullable_buf = p->buffer + buffer_offset;
+					nullable_buf = nullable_buffer + buffer_offset;
 					buffer_offset += size;
-					g_assert (buffer_offset <= 256);
+					g_assert (buffer_offset <= dinfo->nullable_area);
 
 					/* The argument pointed to by arg is either a boxed vtype or null */
 					mono_nullable_init (nullable_buf, (MonoObject*)arg, klass);

mono/mini/mini-arm64.h

@@ -93,7 +93,6 @@ typedef struct {
 	guint8 *ret;
 	double fpregs [FP_PARAM_REGS];
 	int n_fpargs, n_fpret, n_stackargs;
-	guint8 buffer [256];
 	/* This should come last as the structure is dynamically extended */
 	/* The +1 is for r8 */
 	mgreg_t regs [PARAM_REGS + 1];