Re: [Xen-devel] [xen-devel] [Patch v2 2/4] x86/stack: Adjust boundary conditions for printed stacks.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.08.13 at 14:15, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> +/*
> + * Get the bottom-of-stack, as useful for printing stack traces.  This is
> + * similar position as is returned by get_cpu_info(), but works on arbitrary
> + * stack pointer, rather than just the current.
> + *
> + * In the non-frame pointer case, the boundary is exactly at the cpu_info
> + * structure, which prevents the stack trace walker from mis-interpreting
> + * guest register as Xen return addresses.
> + *
> + * For the frame pointer case, the boundary is further adjusted by two words,
> + * as the call out of assembly does not contain a traditional C stack with
> + * frame pointers.
> + */
> +#ifdef CONFIG_FRAME_POINTER
> +#define get_printable_stack_bottom(sp)          \
> +    ((sp & (~(STACK_SIZE-1))) +                 \
> +     (STACK_SIZE - sizeof(struct cpu_info) - 2*sizeof(unsigned long)))
> +#else
> +#define get_printable_stack_bottom(sp)          \
> +    ((sp & (~(STACK_SIZE-1))) + (STACK_SIZE - sizeof(struct cpu_info)))
> +#endif

Hmm, the delta being 2 slots makes no sense to me: The only
difference ought to be the saved frame pointer, i.e. one slot.
With what you propose here I'd suspect that the return address
pointing into assembly code might be lost now with frame pointers.

Jan


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