On Tue, 11 Nov 2025 01:51:55 +0800 Wake Liu wakel@google.com 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/20251108161829.25105-1-ankitkhushwaha.linux@gmai...
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?