assembly - 为什么 "Procedure Call Standard for the ARM Architecture"(AAPCS) 要求 SP 8 字节对齐？

Question

由于这是一个反复出现的主题，因此我提出了一个相关问题。

根据AAPCS :

5.2.1.1 Universal stack constraints

• SP mod 4 = 0. The stack must at all times be aligned to a word boundary

5.2.1.2 Stack constraints at a public interface

• SP mod 8 = 0. The stack must be double-word aligned.

8字节对齐背后的原理是什么？

Answer 1

主要原因是STRD和LDRD只能工作在8字节对齐的地址上。因此，要在堆栈变量上使用它们，堆栈指针需要始终保持 8 字节对齐。

引用ARM Website :

Eight-byte stack alignment is of particular benefit to processors supporting LDRD and STRD instructions, for example, processors based on ARM architecture v5TE and later. If the stack is not eight-byte aligned the use of LDRD and STRD might cause an alignment fault, depending on the target and configuration used.

ARM在这个ABI Advisory Note中也详细解释了它.