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Re: [klibc] kernel/libc uapi changes for y2038
- From: "H. Peter Anvin" <hpa at zytor dot com>
- To: Arnd Bergmann <arnd at arndb dot de>, linux-api at vger dot kernel dot org
- Cc: klibc at zytor dot com, libc-alpha at sourceware dot org, y2038 at lists dot linaro dot org, musl at lists dot openwall dot com, linux-kernel at vger dot kernel dot org, Rich Felker <dalias at libc dot org>, cferris at google dot com, enh at google dot com, "Joseph S. Myers" <joseph at codesourcery dot com>
- Date: Wed, 27 May 2015 08:28:44 -0700
- Subject: Re: [klibc] kernel/libc uapi changes for y2038
- Authentication-results: sourceware.org; auth=none
- References: <2664016 dot bYZKg6FQqR at wuerfel>
On 05/18/2015 02:53 AM, Arnd Bergmann wrote:
> In the patch series I posted recently [1], I introduce new system calls to deal
> with modified data structures, but left the question open on how these should
> be best accessed from libc. The patches introduce a new __kernel_time64_t type
> and based on that five new data structured: struct __kernel_timespec,
> struct __kernel_itimerspec, struct __kernel_stat, struct __kernel_rusage,
> and struct __kernel_timex. This works fine for the case when all libc
> implementations provide their own definitions to user space, but not for
> the simplest case (e.g. klibc) where the user-visible structures come directly
> from the kernel uapi headers.
>
> I still don't know what model the various libc developers prefer, so here is
> an alternative approach, as a patch on top of the previous series:
>
> Now, we rename the original structures to struct __old_kernel_*, and use a
> macro to define either the __old_kernel_* or the __kernel_* structure name
> to the name we actually want in user space, based on a __KERNEL_TIME_BITS
> macro that can be set to either 32 or 64 for 32-bit architectures by
> the libc. Depending on that macro, the compiler will either see one
> of these combinations (for each of the five structures):
>
> a) __BITS_PER_LONG == 32 && __KERNEL_TIME_BITS == 32:
>
> struct timespec based on 32-bit __kernel_time_t
> struct __kernel_timespec based on 64-bit __kernel_time64_t
>
> b) __BITS_PER_LONG == 64 && __KERNEL_TIME_BITS == 64:
>
> struct timespec based on 64-bit __kernel_time_t
> struct __kernel_timespec based on 64-bit __kernel_time64_t
>
> c) __BITS_PER_LONG == 32 && __KERNEL_TIME_BITS == 64:
>
> struct __old_kernel_timespec based on 32-bit __kernel_time_t
> struct timespec based on 64-bit __kernel_time64_t
>
> Would this work for everyone? Any alternative suggestions?
>
It seems to work, except I don't really understand why there is a
difference between (b) and (c).
I also have no problem just having klibc contain its own definitions of
these structures, as long as one can prevent the kernel from defining them.
-hpa