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

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Message-ID: <CAMe9rOrKWTFPdFzdN5d6_zR9bPs8Td-oFgs4ObypbB_sd3GovA@mail.gmail.com>
Date:	Sat, 19 May 2012 18:32:49 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...nel.org>, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, mingo@...nel.org, tglx@...utronix.de,
	Paul Mundt <lethal@...ux-sh.org>,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 08/10] Use __kernel_ulong_t in struct msqid64_ds

On Sat, May 19, 2012 at 4:47 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 05/18/2012 02:21 PM, Arnd Bergmann wrote:
>> On Friday 18 May 2012, H.J. Lu wrote:
>>> Since x32 uses the same kernel interface as x86-64 with a few
>>> exceptions.  The current kernel header files with
>>>
>>> #ifdef __x86_64__
>>> # define __BITS_PER_LONG 64
>>> #else
>>> # define __BITS_PER_LONG 32
>>> #endif
>>>
>>> #if __BITS_PER_LONG == 64
>>> Define x86-64 types
>>> #endif
>>>
>>> work fine for x32 even if long for x32 is 32 bits.  If __BITS_PER_LONG
>>> is changed to 32 for x32, many types in kernel header files will be
>>> wrong for x32.
>>>
>>
>> A lot of things are broken if __BITS_PER_LONG is set to 64 in x32 user
>> space. It was specifically introduced to get around places in exported
>> headers that incorrectly used '#ifdef CONFIG_64BIT' to define a user
>> space structure, so that we can depend on whatever the user sees
>> in bitmasks and other data structures.
>>
>
> I'm not entirely sure I follow the above statement, as it seems
> contradict itself.  Either way, I would agree, __BITS_PER_LONG should be
> 32 in x32 space and if there are places where that is wrong then we need
> to fix them.
>
> Fortunately x32 is littleendian, so no "littleendian bitmask on a
> bigendian architecture" drain bamage...
>

If __BITS_PER_LONG is set to 32 for x32, we need to audit all
exported kernel headers where __BITS_PER_LONG is checked.
If long is used in those places, it has to be updated for x32.

-- 
H.J.
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