Re: [PATCH v4 0/3] tools/accounting: refactor delay fields and share format_timespec()

[Thomas Weißschuh]

On Tue, Aug 04, 2026 at 03:19:21PM +0800, wang.yaxin@xxxxxxxxxx wrote:
> >Thanks.  Sashiko asks one question:
> >    https://sashiko.dev/#/patchset/2026072415043227725SuvoyQ3SGDOmHLp8tdn@xxxxxxxxxx
> >
> >> +/*
> >> + * Copied from include/uapi/linux/time_types.h
> >> + *
> >> + * Uses the arch-dependent __kernel_long_t rather than a hardcoded
> >> + * 'long' so that x32 (ILP32 on x86_64), where the kernel defines
> >> + * __kernel_long_t as 'long long', gets the correct struct layout.
> >> + *
> >> + * __kernel_long_t is provided by <asm/posix_types.h> - included
> >> + * below via <linux/types.h> on most systems, or directly here.
> >> + */
> >[ ... ]
> >> +struct __kernel_old_timespec {
> >> +	__kernel_long_t		tv_sec;
> >> +	long			tv_nsec;
> >Does this hardcoded long for tv_nsec cause an ABI layout mismatch on x32?
> >The header comment above explicitly mentions avoiding a hardcoded long to
> >ensure x32 gets the correct struct layout, but tv_nsec is defined as long
> >here instead of __kernel_long_t. 
> >If tools compile against this header on x32, it looks like they will get a
> >32-bit tv_nsec instead of the 64-bit value expected by the core kernel UAPI,
> >which could result in truncated timestamps or out-of-bounds structure access.
> 
> We cannot replace long with __kernel_long_t for tv_nsec.

The UAPI *is* in fact about to use __kernel_long_t for tv_nsec.
See commit 79ced850e549 ("y2038: uapi: Use 64-bit
__kernel_old_timespec::tv_nsec on x32") in -next.

> struct __kernel_old_timespec is a frozen UAPI type with a fixed layout.
> On x32, the kernel uses long for tv_nsec, producing a 12-byte struct.
> Changing the stub to __kernel_long_t would yield a 16-byte struct,
> breaking sizeof() and struct embedding for any tool that includes
> this header.  tv_nsec only needs 32 bits (range 0..999,999,999), so
> the kernel intentionally uses plain long here.

The 'struct __kernel_old_timespec' as seen by x32 userspace comes from a
x86_64 kernel. And for said kernel this is a 16-byte struct using an 8-byte
tv_nsec.

However this discussion is fairly moot, as x32 is about to be removed.

(...)


Thomas