> On Sep 20, 2017, at 2:07 PM, Josh Poimboeuf <[email protected]> wrote: > >> On Wed, Sep 20, 2017 at 08:01:02PM +0200, Dmitry Vyukov wrote: >>> On Wed, Sep 20, 2017 at 7:46 PM, H. Peter Anvin <[email protected]> wrote: >>>> On 09/20/17 10:38, Dmitry Vyukov wrote: >>>> >>>> I think we need just the frame itself and RSP pointing below this >>>> frame. If we don't have a frame, CALL instruction will smash whatever >>>> RSP happens to point to. Compiler doesn't have to setup RSP to point >>>> below used part of stack in leaf functions. >>>> >>> >>> In the kernel it does. Redzoning is not allowed in the kernel, because >>> interrupts or exceptions would also smash the redzone. >> >> I see... But it's the same for user-space signals, the first thing a >> signal should do is to skip the redzone. I guess interrupt handlers >> should switch to interrupt stack which avoids smashing redzone >> altogether. Do you mean nested interrupts/exceptions in interrupts? >> In my experience frames in leaf functions can have pretty large >> performance penalty. Wonder if we have we considered changing >> interrupt/exception handlers to avoid smashing redzones and disable >> leaf frames? > > Currently, on x86-64, I believe all exceptions have their own dedicated > stacks in the kernel, but IRQs still come in on the task's kernel stack. > > Andy, do you know if there's a reason why IRQs don't use a dedicated IST > stack? >
Because IST is awful due to recursion issues. We immediately switch to an IRQ stack, though. If the kernel wanted a redzone, it would have to use IST for everything, which would entail a bunch of unpleasant hackery. > -- > Josh
