On Sun, Nov 21, 2010 at 4:45 AM, Robert P. J. Day <rpj...@crashcourse.ca>wrote:
> > continuing my journey into the depths of kernel data structures, i'm > curious about the design and usage of list "poisoning". > > first, here are the magic values used to poison list node pointers, > defined in poison.h: > > > #define LIST_POISON1 ((void *) 0x00100100 + POISON_POINTER_DELTA) > #define LIST_POISON2 ((void *) 0x00200200 + POISON_POINTER_DELTA) > > > doesn't really matter what those value are, they're just magic and > immediately identifiable values. and they're used as the new values > for the prev and next pointers of list nodes that are, among other > things, removed from a list. this is from list.h: > > > examples of why the values are always set: http://lkml.org/lkml/2003/12/3/104 http://lkml.org/lkml/2003/6/14/155 even without debugging on, its still immediately obvious when a poisoned pointer is deferenced. And it does matter what the values are, they are set to addresses that won't normally be mapped in order to trigger a fault. This catches programming errors even when full debugging isn't enabled.
