在AArch64 Virtual Memory System Architecture中，有以下几种机制会导致PE在访问memory失败时产生exceptions。
- Debug exception: An exception caused by the debug configuration.
- Alignment fault: An Alignment fault is generated if the address used for a memory access does not have the required alignment for the operation.
- MMU fault: An MMU fault is a fault generated by the fault checking sequence for the current translation regime.
- External abort: Any memory system fault other than a Debug exception, an Alignment fault, or an MMU fault.
这些机制统称为aborts。
当1笔access产生abort时，会使用Fault Address Registers (FARs)和Exception Syndrome Registers (ESRs)去记录context information，方便software debug。
以下列出了这些aborts的特点。
对于exception有synchronous和asynchronous两种，它们的区分如下：
Synchronous exception types有：
Instruction alignment fault应该报PC alignment fault exception。Data access alignment fault应该报Data Abort exception。SP misaligned fault报SP alignment fault exception。instruction fetch的aborts报instruction abort exceptions。
Asynchronous exception types有：
其中physical SError interrupt经常用于memory system里external aborts的asynchronous错误。
