Joe Buck wrote: > On Thu, Dec 17, 2009 at 11:06:13AM -0800, Russell King - ARM Linux wrote: > > On Thu, Dec 17, 2009 at 10:35:17AM -0800, Joe Buck wrote: > > > Besides, didn't I see a whole bunch of kernel security patches related > > > to null pointer dereferences lately? If page 0 can be mapped, you > > > suddenly won't get your trap. > > > > Page 0 can not be mapped on ARM kernels since the late 1990s, and this > > protection is independent of the generic kernel. > > > > Milage may vary on other architectures, but that's not a concern here.
It does not trap on at least one ARM-nommu kernel... > I don't understand, though, why you would want to implement a generally > useful facility (make the kernel trap so you can do a post-mortem > analysis) in a way that's only safe for the ARM port. The patch under discussion, which led to these questions and Cc gcc@gcc.gnu.org, is specific to the ARM architecture and that is Russell's focus, as ARM kernel maintainer. But yes, the whole principle of how to trap and whether it's safe to follow a null pointer dereference with __builtin_unreachable() applies to all the other architectures too. -- Jamie
