linux-kernel - Re: [PATCH 08/10] Use __kernel_ulong_t in struct msqid64

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Date:	Thu, 17 May 2012 20:39:07 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <hpa@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	torvalds@...ux-foundation.org, mingo@...nel.org,
	tglx@...utronix.de, Paul Mundt <lethal@...ux-sh.org>
Subject: Re: [PATCH 08/10] Use __kernel_ulong_t in struct msqid64_ds

On Thu, May 17, 2012 at 8:21 PM, H. Peter Anvin <hpa@...nel.org> wrote:
> On 05/17/2012 04:51 PM, H. Peter Anvin wrote:
>>
>> This patch and the one before it seems to have another problem: we
>> currently define __BITS_PER_LONG as:
>>
>> #ifdef __x86_64__
>> # define __BITS_PER_LONG 64
>> #else
>> # define __BITS_PER_LONG 32
>> #endif
>>
>
> H.J., do you see any problem *other* than this wretched struct
> msqid64_ds with changing the above from __x86_64__ to
>
> #if defined(__x86_64__) && !defined(__ILP32__)
>
> ... in the above?
>
> As far as struct msqid64_ds,  I think we can fix it simply because x86
> is the only compat-aware architecture which has to deal with it.
>
> (Incidentally, if sh is ever expanded to 64 bits, it will have a problem
> in the bigendian configuration...)

That will be wrong.   __BITS_PER_LONG defines # bits of long
as seen by kernel.  We don't use it in user space.  Remember
x32 uses the identical interface as x86-64.  So

#ifdef __x86_64__
# define __BITS_PER_LONG 64
#else
# define __BITS_PER_LONG 32
#endif

struct msqid64_ds {
        struct ipc64_perm msg_perm;
        __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;
#endif

are absolutely correct for x32.  You can think

#if __BITS_PER_LONG != 64

as

#ifndef __x86_64__

which is used in glibc.


-- 
H.J.
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