如果我有一个C函数并且我用gdb调试它，我如何找到函数的返回值？

Question

我有一个作业，要求我找到主要的寄存器检查的返回值（我们正在学习gdb），我将如何去做呢？

Answer 1

In general, look at the calling convention.

In x86, all calling conventions return small integer results on EAX, and large (64-bit) results on EDX:EAX (EDX holding the higher bits), and floating point results in FP0.

In x64, small integer results are returned on RAX, and floating point results in FP0.

In ARM (including thumb-mode), integer results are returned in R0.

If you're trying to work out where to put your breakpoint, my suggestion is to put a breakpoint at the start of the main function. If you do that, the return address (ie where main will return to once it is finished executing) will be the value on the top of the stack. If you put a breakpoint there, you'll break just after the main function has finished executing.

Since main has the return type of int , you can look at EAX (or RAX or R0) to see what value main returned.