使用格式获取属性ToString(Get property ToString with formatting)

 在装配级别没有“未定义的内存”这样的东西。 只要行为符合预期，gcc就可以自由发出以其认为合适的方式访问堆栈的代码。 
 
 我猜测为什么会发生这种情况，这是一个叶子函数，调整堆栈指针是徒劳的。 您可以尝试通过检查程序集中的任何call指令来验证这一点。 （您也可以检查C源，但内联可能会使其不那么可靠。） 
 
 某些平台的ABI明确允许这种欺骗，包括x86-64。 从AMD64 ABI文档 ： 
 
 
 
 超出％rsp指向的位置的128字节区域被认为是保留的，不应被信号或中断处理程序修改。 因此，函数可以将此区域用于函数调用不需要的临时数据。 特别是，叶子函数可以将这个区域用于它们的整个堆栈帧，而不是调整序言和尾声中的堆栈指针。 这个区域被称为红区。 
 
 
 这篇博文可能会对这个主题进行有趣的阅读。 

There's no such thing as "undefined memory" at the assembly level. gcc is free to emit code that accesses the stack in whatever way it sees fit, so long as the behaviour is as expected.
 
My guess as to why this is happening is that this is a leaf function for which adjusting the stack pointer is fruitless. You could try to verify that by inspecting the assembly for any call instructions. (You could also inspect the C source, but inlining may make that a bit less reliable.)
 
This kind of trickery is explicitly allowed by the ABI of certain platforms, including x86-64. From the AMD64 ABI documentation:
 
 
 
The 128-byte area beyond the location pointed to by %rsp is considered to be reserved and shall not be modified by signal or interrupt handlers. Therefore, functions may use this area for temporary data that is not needed across function calls. In particular, leaf functions may use this area for their entire stack frame, rather than adjusting the stack pointer in the prologue and epilogue. This area is known as the red zone.
 
 
This blog post might make for interesting reading on the subject.