On Fri, 2022-05-06 at 19:12 +1000, Finn Thain wrote: > > On Thu, 5 May 2022, Bjorn Helgaas wrote: > > > On Thu, May 05, 2022 at 07:39:42PM +0200, Arnd Bergmann wrote: > > > On Thu, May 5, 2022 at 6:10 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > > On Wed, May 04, 2022 at 11:31:28PM +0200, Arnd Bergmann wrote: > > > > > The main goal is to avoid c), which is what happens on s390, but > > > > > can also happen elsewhere. Catching b) would be nice as well, > > > > > but is much harder to do from generic code as you'd need an > > > > > architecture specific inline asm statement to insert a ex_table > > > > > fixup, or a runtime conditional on each access. > > > > > > > > Or s390 could implement its own inb(). > > > > > > > > I'm hearing that generic powerpc kernels have to run both on machines > > > > that have I/O port space and those that don't. That makes me think > > > > s390 could do something similar. > > > > > > No, this is actually the current situation, and it makes absolutely no > > > sense. s390 has no way of implementing inb()/outb() because there > > > are no instructions for it and it cannot tunnel them through a virtual > > > address mapping like on most of the other architectures. (it has special > > > instructions for accessing memory space, which is not the same as > > > a pointer dereference here). > > > > > > The existing implementation gets flagged as a NULL pointer dereference > > > by a compiler warning because it effectively is. > > > > I think s390 currently uses the inb() in asm-generic/io.h, i.e., > > "__raw_readb(PCI_IOBASE + addr)". I understand that's a NULL pointer > > dereference because the default PCI_IOBASE is 0. > > > > I mooted a s390 inb() implementation like "return ~0" because that's > > what happens on most arches when there's no device to respond to the > > inb(). > > > > The HAS_IOPORT dependencies are fairly ugly IMHO, and they clutter > > drivers that use I/O ports in some cases but not others. But maybe > > it's the most practical way. > > > > Do you mean, "the most practical way to avoid a compiler warning on s390"? > What about "#pragma GCC diagnostic ignored"? This actually happens with clang. Apart from that, I think this would also fall under the same argument as the original patch Linus unpulled. We would just paint over someting that we know at compile time won't work: https://lore.kernel.org/lkml/CAHk-=wg80je=K7madF4e7WrRNp37e3qh6y10Svhdc7O8SZ_-8g@xxxxxxxxxxxxxx/
