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? -- Josh
