On Mon, 2021-05-03 at 18:07 +0200, Arnd Bergmann wrote:
> On Fri, Apr 30, 2021 at 1:16 PM Niklas Schnelle <schnelle@xxxxxxxxxxxxx> wrote:
> > From: Niklas Schnelle <niklas@xxxxxxxxx>
> >
> > This is version 4 of my attempt to get rid of a clang
> > -Wnull-pointer-arithmetic warning for the use of PCI_IOBASE in
> > asm-generic/io.h. This was originally found on s390 but should apply to
> > all platforms leaving PCI_IOBASE undefined while making use of the inb()
> > and friends helpers from asm-generic/io.h.
> >
> > This applies cleanly and was compile tested on top of v5.12 for the
> > previously broken ARC, nds32, h8300 and risc-v architecture
> >
> > I did boot test this only on x86_64 and s390x the former implements
> > inb() itself while the latter would emit a WARN_ONCE() but no drivers
> > use inb().
>
> This looks all fine to me, but with the merge window open right now, I
> can't add it into linux-next yet, and it wouldn't qualify as a bugfix for 5.13.
>
> Please resend them to me after -rc1 is out so I can merge it for
> 5.14 through the asm-generic tree.
Thanks for the great feedback I appreciate it. Will do the resend of
course.
>
> Please add two small changes to the changelog texts:
>
> - for patch 3, please include a 'Link: tag' to the lore archive of the
> previous discussion, that should cover any questions that people
> may have
Done
>
> - for the risc-v patch, I would suggest explaining that this fixes
> an existing runtime bug, not just a compiler error:
> | This is already broken, as accessing a fixed I/O port number of
> | an ISA device on NOMMU RISC-V would turn into a NULL pointer
> | dereference.
> Feel free to either copy this, or use your own explanation.
I mixed the above in with the current commit message:
Without MMU support PCI_IOBASE is left undefined because PCI_IO_END is
VMEMMAP_START. Nevertheless the in*()/out*() helper macros are left
defined with uses of PCI_IOBASE. At the moment this only compiles
because asm-generic/io.h defines PCI_IOBASE as 0 if it is undefined and
so at macro expansion PCI_IOBASE is defined. This leads to compilation
errors when asm-generic/io.h is changed to leave PCI_IOBASE undefined.
More importantly it is currently broken at runtime, as accessing a fixed
I/O port number of an ISA device on NOMMU RISC-V would turn into a NULL
pointer dereference. Instead only define the in*()/out*() helper macros
with MMU support and fall back to the asm-generic/io.h helper stubs
otherwise.
>
> Arnd
