On Tue, 17 Mar 2026 00:07:57 +0100 "Arnd Bergmann" <[email protected]> wrote:
> On Mon, Mar 16, 2026, at 23:51, Matt Roper wrote: > > On Mon, Mar 16, 2026 at 11:43:46PM +0100, Arnd Bergmann wrote: > >> From: Arnd Bergmann <[email protected]> > >> > >> ptrdiff_t, size_t and long are the same size on all supported > >> architectures, > >> but gcc requires the use of the %zx modifier instead of %lx. On 32-bit > > > > Nathan Chancellor just sent a fix here: > > > > https://lore.kernel.org/all/20260316-drm-xe-fix-32-bit-wformat-ptrdiff-v1-1-0108b10b2...@kernel.org/ > > > > His solution uses %tx rather than %zx, which according to > > Documentation/core-api/printk-formats.rst sounds like it's probably the > > most accurate format string for this case? > > > > Right, Nathan's version is correct. I wasn't aware that size_t > and ptrdiff_t have different modifiers. Consider: void foo(size_t len) { char *p = malloc(len); char *end = p + len; ptrdiff_t diff = p - end; printf("len %zu, diff %td\n", len, diff); free(p); } Clearly foo(5) output "5 -5". But what about foo(5u << 29) on a 32bit system with a large unlimit and a big enough hole in the address space. More likely would be something running on an x86 in real mode. There malloc(65000) might be reasonable, so size_t would be unsigned int but ptrdiff_t would need to be a signed 32bit type. Of course, in linux, they are all 'long'. David > > Arnd >
