Hi! > > This is quite clever, but now I???m wondering just how much kernel help > > is really needed. In your series, the trampoline is an non-executable > > page. I can think of at least two alternative approaches, and I'd > > like to know the pros and cons. > > > > 1. Entirely userspace: a return trampoline would be something like: > > > > 1: > > pushq %rax > > pushq %rbc > > pushq %rcx > > ... > > pushq %r15 > > movq %rsp, %rdi # pointer to saved regs > > leaq 1b(%rip), %rsi # pointer to the trampoline itself > > callq trampoline_handler # see below > > For nested calls (where the trampoline needs to pass the > original stack frame to the nested function) I think you > just need a page full of: > mov $0, scratch_reg; jmp trampoline_handler I believe you could do with mov %pc, scratch_reg; jmp ... That has advantage of being able to share single physical page across multiple virtual pages... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
