On Tue, 11 Nov 2025 01:51:55 +0800 Wake Liu <[email protected]> wrote:
> The compiler warns about a tautological comparison in mremap_test.c: > "pointer comparison always evaluates to false [-Wtautological-compare]" > > This occurs when checking for unsigned overflow: > if (addr + c.dest_alignment < addr) > > Cast 'addr' to 'unsigned long long' to ensure the comparison is performed > with a wider type, correctly detecting potential overflow and resolving > the warning. > Thanks. I recently merged https://lore.kernel.org/all/[email protected]/T/#u there has been some discussion... > --- a/tools/testing/selftests/mm/mremap_test.c > +++ b/tools/testing/selftests/mm/mremap_test.c > @@ -1032,7 +1032,7 @@ static long long remap_region(struct config c, unsigned > int threshold_mb, > /* Don't destroy existing mappings unless expected to overlap */ > while (!is_remap_region_valid(addr, c.region_size) && !c.overlapping) { > /* Check for unsigned overflow */ > - if (addr + c.dest_alignment < addr) { > + if ((unsigned long long)addr + c.dest_alignment < (unsigned > long long)addr) { > ksft_print_msg("Couldn't find a valid region to remap > to\n"); > ret = -1; > goto clean_up_src; I wonder if we'd be better off borrowing ideas from include/linux/overflow.h:check_add_overflow(). Did anyone try __builtin_add_overflow() here?
