如何在信号处理程序中获取执行上下文？

Question

I am getting illegal operand error when I run a program. The program where the crash happens is written in assembly and linked as an object file, so I'm not sure how to use gdb with it. I noticed the fault by trapping the SIGILL signal.I want to get the address of the offending instruction. One method that comes to my mind is to get the last execution context in the signal handler and note down the value of rip register from it. I know that context is passed to signal handlers, but don't know how.

Answer 1

If you do want to follow the signal handler route it is not hard to get the address of the instruction that causes the signal handler to run. When you create your signal handler set the SA_SIGINFO bit in the flags setting. Then when you write your handler it will have access to a siginfo_t structure that includes the field si_addr which is the address of the memory location that triggered the exception.

Answer 2

written in assembly and linked as an object file, so I'm not sure how to use gdb with it

GDB is perfectly fine for debugging assembly code. You'll want info registers , x/i $pc .

One method that comes to my mind is to get the last execution context in the signal handler and note down the value of rip register from it.

That's fine (see Gabriel's answer on how to get the context).

Please note that this will not give you any additional info compared to what you get inside GDB at crash point. If you didn't know how to use GDB in the first place, then I don't see what you'll gain by getting the context in a signal handler.