On Mon, Nov 20, 2017 at 12:46:13PM -0800, Andy Lutomirski wrote: > On Mon, Nov 20, 2017 at 12:42 PM, Josh Poimboeuf <jpoim...@redhat.com> wrote: > > On Mon, Nov 20, 2017 at 09:07:33AM -0800, Andy Lutomirski wrote: > >> +bool in_SYSENTER_stack(unsigned long *stack, struct stack_info *info) > > > > Can you make it lowercase for consistency with the other in_*_stack() > > functions? For example, in_irq_stack() is all lowercase even though > > "IRQ" is normally written in uppercase. > > > > But also, I'm wondering whether this get_stack_info() support is even > > really needed. > > > > As currently written, the trampoline code doesn't have any ORC data > > associated with it. So the unwinder would never have the need to > > actually read the SYSENTER stack. > > > > You _could_ add an UNWIND_HINT_IRET_REGS annotation after the simulated > > iret frame is written, which would allow the unwinder to dump those regs > > when unwinding from an NMI. > > There's some ORC data in the non-trampoline SYSENTER path
But that's *after* the stack switch to the real kernel stack, right? > but, more importantly, the OOPS unwinder will just bail without this > patch. With the patch, we get a valid unwind, except that everything > has a ? in front. Hm. I can't even fathom how that's possible. Are you talking about the "unwind from NMI to SYSENTER stack" path? Or any unwind to a syscall? Either way I'm baffled... If the unwinder only encounters the SYSENTER stack at the end, how could that cause everything beforehand to have a question mark? > > But there's only a tiny window where that would be possible: only a few > > instructions. I'm not sure that would be worth the effort, unless we > > got to the point where we expect to have 100% unwinder coverage. But > > that's currently unrealistic anyway because of generated code and > > runtime patching. > > I tripped it myself several times when debugging this code. Again I don't see how this patch would help if there's no ORC data for the code which uses the SYSENTER stack. I must be missing something. -- Josh
