Search code examples
assemblyx86-64cpu-registersinterrupt-handlingisr

How to save the registers on x86_64 for an interrupt service routine?

I am looking at some old code from a school project, and in trying to compile it on my laptop I ran into some problems. It was originally written for an old 32 bit version of gcc. Anyway I was trying to convert some of the assembly over to 64 bit compatible code and hit a few snags.

Here is the original code:

pusha
pushl   %ds
pushl   %es
pushl   %fs
pushl   %gs
pushl   %ss

pusha is not valid in 64 bit mode. So what would be the proper way to do this in x86_64 assembly while in 64 bit mode?

There has got to be a reason why pusha is not valid in 64 bit mode, so I have a feeling manually pushing all the registers may not be a good idea.

Solution

  • Learn from existing code that does this kind of thing. For example:

    In fact, "manually pushing" the regs is the only way on AMD64 since PUSHA doesn't exist there. AMD64 isn't unique in this aspect - most non-x86 CPUs do require register-by-register saves/restores as well at some point.

    But if you inspect the referenced sourcecode closely you'll find that not all interrupt handlers require to save/restore the entire register set, so there is room for optimizations.