On Fri, Dec 01, 2023 at 10:12:48AM +0100, Ard Biesheuvel wrote: > It appears the sub instruction at 0x6dd0 correctly accounts for the > extra 8 bytes, so the frame pointer is valid. So it is our assumption > that there are no gaps between the stack frames is invalid. > > Could you try the following change please? > > --- a/arch/arm/kernel/ftrace.c > +++ b/arch/arm/kernel/ftrace.c > @@ -235,8 +235,12 @@ > return; > > if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER)) { > - /* FP points one word below parent's top of stack */ > - frame_pointer += 4; > + /* > + * The top of stack of the parent is recorded in the stack > + * frame at offset [fp, #-8]. > + */ > + get_kernel_nofault(frame_pointer, > + (unsigned long *)(frame_pointer - 8));
Yes, this will get the value of the stack pointer when the function was entered - which may be the bottom of the parent function's stack _or_ the start of non-register arguments to this function. So your replacement has always been more correct. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!