On Sat, Jul 31, 2021 at 9:34 PM Segher Boessenkool <seg...@kernel.crashing.org> wrote: > > On Thu, Jul 29, 2021 at 04:08:36PM +0000, Joseph Myers wrote: > > On Thu, 29 Jul 2021, Florian Weimer via Gcc wrote: > > > On GNU/Linux, SEGFS is used to implement the thread pointer, to avoid > > > dedicating a general-purpose register to it. At address zero with the > > > SEGFS prefix, the offset itself is stored so that userspace can read it > > > without having to call into the kernel. So the SEGFS null pointer is a > > > valid address, and so are some bytes after it (depending on TCB layout, > > > some of which is specified by the ABI or is part of the de-facto ABI > > > used by GCC). > > > > That suggests that we need a target hook to describe null pointer > > properties for a given address space. In an address space where null > > pointers are valid to dereference, there should be no diagnostics for > > arithmetic on / dereferencing them - and more generally, > > -fno-delete-null-pointer-checks should be in effect for pointers to such > > an address space (so I don't think this is just a warning issue, you can > > probably get wrong code from null pointer check deletion in such an > > address space). > > There already is TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID? So this just > isn't used everywhere it should?
Yeah, looks like so. Richard. > > Segher
