(added Nathan for clang advice) On Fri, Nov 07, 2025 at 04:08:55PM -0800, Andrew Morton wrote: > On Fri, 7 Nov 2025 10:27:27 +0100 "David Hildenbrand (Red Hat)" > <[email protected]> wrote: > > > On 06.11.25 13:02, Ankit Khushwaha wrote: > > > On Thu, Nov 06, 2025 at 12:18:57PM +0100, David Hildenbrand (Red Hat) > > > wrote: > > >> On 06.11.25 11:49, Ankit Khushwaha wrote: > > >>> Pointer arthemitic with 'void * addr' and 'unsigned long long > > >>> dest_alignment' > > >>> triggers following warning: > > >>> > > >>> mremap_test.c:1035:31: warning: pointer comparison always evaluates to > > >>> false [-Wtautological-compare] > > >>> 1035 | if (addr + c.dest_alignment < addr) { > > >>> | ^ > > >>> > > >>> typecasting 'addr' to 'unsigned long long' to fix pointer comparison. > > >> > > >> With which compiler are you seeing this? > > > > > > Hi David, > > > > > > clang version 20.1.8 (Fedora 20.1.8-4.fc42) raised this warning. > > > > > > To reproduce: > > > make -C tools/testing/selftests/mm CC=clang > > > > Thanks, and thanks to Lorenzo for the details. > > > > Acked-by: David Hildenbrand (Red Hat) <[email protected]> > > I must say, applying this would be an unhappy life event. > > if (void* + ulong < void*) > > makes perfect sense in a world which permits void* arithmetic (ie, > ours). So what the heck is clang doing?? > > If we do > > void *addr2 = addr + c.dest_alignment; > if (addr2 < addr) > ... > > then which statement warns, and why?
-- Sincerely yours, Mike.
