Hi Michael, On Wed, May 01, 2024 at 12:04:40AM +1000, Michael Ellerman wrote: > With -Wextra clang warns about pointer arithmetic using a null pointer. > When building with CONFIG_PCI=n, that triggers a warning in the IO > accessors, eg: > > In file included from linux/arch/powerpc/include/asm/io.h:672: > linux/arch/powerpc/include/asm/io-defs.h:23:1: warning: performing pointer > arithmetic on a null pointer has undefined behavior > [-Wnull-pointer-arithmetic] > 23 | DEF_PCI_AC_RET(inb, u8, (unsigned long port), (port), pio, port) > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > ... > linux/arch/powerpc/include/asm/io.h:591:53: note: expanded from macro > '__do_inb' > 591 | #define __do_inb(port) readb((PCI_IO_ADDR)_IO_BASE + port); > | ~~~~~~~~~~~~~~~~~~~~~ ^ > > That is because when CONFIG_PCI=n, _IO_BASE is defined as 0. > > There is code that builds with calls to IO accessors even when > CONFIG_PCI=n, but the actual calls are guarded by runtime checks. > If not those calls would be faulting, because the page at virtual > address zero is (usually) not mapped into the kernel. As Arnd pointed > out, it is possible a large port value could cause the address to be > above mmap_min_addr which would then access userspace, which would be > a bug. > > To avoid any such issues, and also fix the compiler warning, set the > _IO_BASE to POISON_POINTER_DELTA. That is a value chosen to point into > unmapped space between the kernel and userspace, so any access will > always fault. > > Reported-by: Naresh Kamboju <naresh.kamb...@linaro.org> > Closes: > https://lore.kernel.org/all/CA+G9fYtEh8zmq8k8wE-8RZwW-Qr927RLTn+KqGnq1F=ptaa...@mail.gmail.com > Signed-off-by: Michael Ellerman <m...@ellerman.id.au> > --- > arch/powerpc/include/asm/io.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/io.h b/arch/powerpc/include/asm/io.h > index 08c550ed49be..1cd6eb6c8101 100644 > --- a/arch/powerpc/include/asm/io.h > +++ b/arch/powerpc/include/asm/io.h > @@ -37,7 +37,7 @@ extern struct pci_dev *isa_bridge_pcidev; > * define properly based on the platform > */ > #ifndef CONFIG_PCI > -#define _IO_BASE 0 > +#define _IO_BASE POISON_POINTER_DELTA
This works for CONFIG_PPC64 but not CONFIG_PPC32 (so tinyconfig and allnoconfig like Naresh reported) because CONFIG_ILLEGAL_POINTER_VALUE is defined as 0 in that case. $ grep -P 'CONFIG_(ILLEGAL_POINTER_VALUE|PCI|PPC32)' .config CONFIG_PPC32=y CONFIG_ILLEGAL_POINTER_VALUE=0 > #define _ISA_MEM_BASE 0 > #define PCI_DRAM_OFFSET 0 > #elif defined(CONFIG_PPC32) > -- > 2.44.0 >
