On Fri, May 10, 2019 at 01:58:31PM +0900, Masami Hiramatsu wrote: > On Thu, 9 May 2019 19:14:16 +0200 > Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > Ideally also the optimized kprobe trampoline, but I've not managed to > > fully comprehend that one. > > As you pointed in other reply, save/restore can be a macro, but > each trampoline code is slightly different. Optprobe template has > below parts > > (jumped from probed address) > [store regs] > [setup function arguments (pt_regs and probed address)] > [handler call] > [restore regs] > [execute copied instruction] instruction_s_ ? The JMP to this trampoline is likely 5 bytes and could have clobbered multiple instructions, we'd then have to place them all here, and > [jump back to probed address] jump to after whatever instructions were clobbered by the JMP. > Note that there is a limitation that if it is optiomized probe, user > handler can not change regs->ip. (we can not use "ret" after executed > a copied instruction, which must run on same stack) Changing regs->ip in this case is going to be massively dodgy indeed :-) But so would changing much else; changing stack layout would also be somewhat tricky.
