> On Feb 20, 2015, at 12:01 PM, Jeff Law <l...@redhat.com> wrote: > > ... > Regardless, the right thing to do is to disable elimination of NULL pointer > checks on targets where page 0 is mapped and thus a reference to *0 may not > fault. In my mind this is an attribute of both the processor (see H8 above) > and/or the target OS. > > On those targets the C-runtime had better also ensure that its headers aren't > decorated with non-null attributes, particularly for the mem* and str* > functions.
pdp11 is an example of such a target, independent of OS (with only 8 pages, clearly no one is going to unmap page 0). Fortunately there one is unlikely to find C program data structures at 0 (instead, vectors if kernel, stack limit if user mode). So no fault is correct there, but no null (0 bits) pointer is also — for practical purposes — a valid assumption.
