linux-kernel - Re: [PATCH v3 01/17] y2038: asm-generic: Extend sysvipc data structures

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Message-ID: <CAK8P3a196QYoM1egagMuZw4WhiwRiO83Qpj0CxoCeVQBEaj-gw@mail.gmail.com>
Date:   Thu, 19 Apr 2018 17:20:26 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        GNU C Library <libc-alpha@...rceware.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Albert ARIBAUD <albert.aribaud@...ev.fr>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        "open list:RALINK MIPS ARCHITECTURE" <linux-mips@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        sparclinux <sparclinux@...r.kernel.org>
Subject: Re: [PATCH v3 01/17] y2038: asm-generic: Extend sysvipc data structures

On Thu, Apr 19, 2018 at 4:59 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Arnd Bergmann <arnd@...db.de> writes:
>>
>>  struct msqid64_ds {
>>       struct ipc64_perm msg_perm;
>> +#if __BITS_PER_LONG == 64
>>       __kernel_time_t msg_stime;      /* last msgsnd time */
>> -#if __BITS_PER_LONG != 64
>> -     unsigned long   __unused1;
>> -#endif
>>       __kernel_time_t msg_rtime;      /* last msgrcv time */
>> -#if __BITS_PER_LONG != 64
>> -     unsigned long   __unused2;
>> -#endif
>>       __kernel_time_t msg_ctime;      /* last change time */
>> -#if __BITS_PER_LONG != 64
>> -     unsigned long   __unused3;
>> +#else
>> +     unsigned long   msg_stime;      /* last msgsnd time */
>> +     unsigned long   msg_stime_high;
>> +     unsigned long   msg_rtime;      /* last msgrcv time */
>> +     unsigned long   msg_rtime_high;
>> +     unsigned long   msg_ctime;      /* last change time */
>> +     unsigned long   msg_ctime_high;
>>  #endif
>
> 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.

        Arnd