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Re: [PATCH v3 01/17] y2038: asm-generic: Extend sysvipc data structures
- From: Arnd Bergmann <arnd at arndb dot de>
- To: "Eric W. Biederman" <ebiederm at xmission dot com>
- Cc: y2038 Mailman List <y2038 at lists dot linaro dot org>, Linux Kernel Mailing List <linux-kernel at vger dot kernel dot org>, Linux API <linux-api at vger dot kernel dot org>, linux-arch <linux-arch at vger dot kernel dot org>, GNU C Library <libc-alpha at sourceware dot org>, Thomas Gleixner <tglx at linutronix dot de>, Deepa Dinamani <deepa dot kernel at gmail dot com>, Al Viro <viro at zeniv dot linux dot org dot uk>, Albert ARIBAUD <albert dot aribaud at 3adev dot fr>, linux-s390 <linux-s390 at vger dot kernel dot org>, Martin Schwidefsky <schwidefsky at de dot ibm dot com>, "the arch/x86 maintainers" <x86 at kernel dot org>, Catalin Marinas <catalin dot marinas at arm dot com>, Will Deacon <will dot deacon at arm dot com>, "open list:RALINK MIPS ARCHITECTURE" <linux-mips at linux-mips dot org>, James Hogan <jhogan at kernel dot org>, Ralf Baechle <ralf at linux-mips dot org>, linuxppc-dev <linuxppc-dev at lists dot ozlabs dot org>, sparclinux <sparclinux at vger dot kernel dot org>
- Date: Thu, 19 Apr 2018 23:24:36 +0200
- Subject: Re: [PATCH v3 01/17] y2038: asm-generic: Extend sysvipc data structures
- References: <20180419143737.606138-1-arnd@arndb.de> <20180419143737.606138-2-arnd@arndb.de> <87efjbnswr.fsf@xmission.com> <CAK8P3a196QYoM1egagMuZw4WhiwRiO83Qpj0CxoCeVQBEaj-gw@mail.gmail.com>
On Thu, Apr 19, 2018 at 5:20 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Thu, Apr 19, 2018 at 4:59 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
>> I suspect you want to use __kernel_ulong_t here instead of a raw
>> unsigned long. If nothing else it seems inconsistent to use typedefs
>> in one half of the structure and no typedefs in the other half.
>
> Good catch, there is definitely something wrong here, but I think using
> __kernel_ulong_t for all members would also be wrong, as that
> still changes the layout on x32, which effectively is
>
> struct msqid64_ds {
> ipc64_perm msg_perm;
> u64 msg_stime;
> u32 __unused1;
> /* 32 bit implict padding */
> u64 msg_rtime;
> u32 __unused2;
> /* 32 bit implict padding */
> u64 msg_ctime;
> u32 __unused3;
> /* 32 bit implict padding */
> __kernel_pid_t shm_cpid; /* pid of creator */
> __kernel_pid_t shm_lpid; /* pid of last operator */
> ....
> };
>
> The choices here would be to either use a mix of
> __kernel_ulong_t and unsigned long, or taking the x32
> version back into arch/x86/include/uapi/asm/ so the
> generic version at least makes some sense.
>
> I can't use __kernel_time_t for the lower half on 32-bit
> since it really should be unsigned.
After thinking about it some more, I conclude that the structure is simply
incorrect on x32: The __kernel_ulong_t usage was introduced in 2013
in commit b9cd5ca22d67 ("uapi: Use __kernel_ulong_t in struct
msqid64_ds") and apparently was correct initially as __BITS_PER_LONG
evaluated to 64, but it broke with commit f4b4aae18288 ("x86/headers/uapi:
Fix __BITS_PER_LONG value for x32 builds") that changed the value
of __BITS_PER_LONG and introduced the extra padding in 2015.
The same change apparently also broke a lot of other definitions, e.g.
$ echo "#include <linux/types.h>" | gcc -mx32 -E -xc - | grep -A3
__kernel_size_t
typedef unsigned int __kernel_size_t;
typedef int __kernel_ssize_t;
typedef int __kernel_ptrdiff_t;
Those used to be defined as 'unsigned long long' and 'long long'
respectively, so now all kernel interfaces using those on x32
became incompatible!
Arnd