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Message-ID: <4A6D76DB.1050902@monstr.eu>
Date: Mon, 27 Jul 2009 11:43:55 +0200
From: Michal Simek <monstr@...str.eu>
To: Arnd Bergmann <arnd@...db.de>
CC: Linux Kernel list <linux-kernel@...r.kernel.org>,
John Williams <john.williams@...alogix.com>
Subject: Re: generic uaccess.h
Arnd Bergmann wrote:
> On Friday 24 July 2009, Michal Simek wrote:
>> I have just look at asm-generic uaccess.h and there is one thing which
>> seems to me wrong.
>>
>> For put_user macro - you use __copy_to_user but you have for 64bit case
>> ifdef CONFIG_64BIT
>> but look at fs/eventfd: eventfd_read function. At least for this
>> function(syscall) is necessary "return" 64bit
>> value on 32bit machines too.
>> IMHO that ifdef CONFIG_64BIT shouldn't be there.
>>
>> What do you think?
>> If you agree with me, I'll generate proper patch with description.
>
> The code was intentional, because 32 bit architectures normally
> don't acces u64 values efficiently. I would expect the memcpy
> to produce better object code in that case.
> Did you see an actual bug in my version or are you only
> guessing that the assignment should work better than the
> memcpy?
>
> What object code do you get with
>
> int test(unsigned long long __user *out, unsigned long long in)
> {
> return put_user(in, ptr);
> }
>
> in both cases?
I found that I have problem on noMMU with replacing
put_user macro
with
#define put_user(x, ptr) \
({ \
might_sleep(); \
access_ok(VERIFY_WRITE, ptr, sizeof(*ptr)) ? \
__put_user(x, ptr) : \
-EFAULT; \
})
(The similar issue is for get_user) (__put_user function is origin - not asm-generic)
I am getting any short write error. It is caused with adding access_ok macro.
It is weird.
RPC: Registered tcp transport module.
VFS: Mounted root (romfs filesystem) readonly on device 31:0.
Freeing unused kernel memory: 100k freed
0: short write
Kernel panic - not syncing: Attempted to kill init!
I have more important work in front of me - I take a look at it later.
Michal
>
> Arnd <><
--
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
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