On Thu, Dec 17, 2009 at 07:38:26PM +0000, Jamie Lokier wrote: > 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 was going to say the following in a different reply but discarded it because it wasn't relevant to the GCC list. I regard ARM nommu as highly experimental, especially as the maintainer vanished half way through merging it into mainline. I know that there are some parts of ARM nommu that are highly buggy - such as ARM940 support invalidating the entire data cache on any DMA transaction... say goodbye stacked return addresses. As such, I would not be surprised if the ARM nommu kernel has _lots_ of weird and wonderful bugs. I am not surprised that NULL pointer dereferences don't work - its actually something I'd expect given that they have a protection unit which the kernel doesn't apparently touch. Maybe the protection unit code never got merged? I've no idea. As I say, uclinux support got as far as being half merged and that's roughly the state it's remained in ever since. We don't even have any no-MMU configurations which the kernel builder automatically tests for us. Given the lack of progress/bug reporting on ARM uclinux, the lack of platform support and the lack of configurations, my view is that there is no one actually using it. I know that I don't particularly take any care with respect to uclinux when making changes to the MMU based kernels. Why bother if apparantly no one's using it?
