linux-kernel - Re: [PATCH] nios2: __kuser

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Message-ID: <54C0BDEB.80809@codesourcery.com>
Date:	Thu, 22 Jan 2015 17:07:55 +0800
From:	Chung-Lin Tang <cltang@...esourcery.com>
To:	Ley Foon Tan <lftan@...era.com>
CC:	Chung-Lin Tang <chunglin.tang@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tobias Klauser <tklauser@...tanz.ch>
Subject: Re: [PATCH] nios2: __kuser_sigtramp placement fix

On 2015/1/22 下午 04:43, Ley Foon Tan wrote:
> On Thu, Jan 22, 2015 at 4:15 PM, Chung-Lin Tang <cltang@...esourcery.com> wrote:
>> On 2015/1/22 03:54 PM, Ley Foon Tan wrote:
>>> On Thu, Jan 22, 2015 at 3:14 PM, Chung-Lin Tang <chunglin.tang@...il.com> wrote:
>>>> The address of __kuser_sigtramp is wrong by one word, due to padding
>>>> __kuser_cmpxchg to fully 64 bytes. The version word at the start of the
>>>> page displaces __kuser_sigtramp to 0x1044, instead of the intended 0x1040.
>>>>
>>>> Fixed by counting the 64-byte frame from the start of the page instead
>>>> of __kuser_cmpxchg. This shortens the __kuser_cmpxchg frame to 60-bytes,
>>>> but that's likely enough.
>>>>
>>>> The zero-byte padding parts of the kuser_pad macro has been removed, due
>>>> to the .if command refusing to behave properly when there are other
>>>> .word directives in between. Probably a binutils gas bug.
>>>>
>>>> Thanks,
>>>> Chung-Lin
>>>>
>>>> Cc: Ley Foon Tan <lftan@...era.com>
>>>> Cc: Tobias Klauser <tklauser@...tanz.ch>
>>>> Signed-off-by: Chung-Lin Tang <cltang@...esourcery.com>
>>>>
>>>> diff --git a/arch/nios2/kernel/entry.S b/arch/nios2/kernel/entry.S
>>>> index 0bdfd13..3224839 100644
>>>> --- a/arch/nios2/kernel/entry.S
>>>> +++ b/arch/nios2/kernel/entry.S
>>>> @@ -492,14 +492,7 @@ ENTRY(ret_from_kernel_thread)
>>>>
>>>>   /* Filling pads with undefined instructions. */
>>>>  .macro kuser_pad sym size
>>>> -       .if     ((. - \sym) & 3)
>>>> -       .rept   (4 - (. - \sym) & 3)
>>>> -       .byte   0
>>>> -       .endr
>>>> -       .endif
>>>> -       .rept   ((\size - (. - \sym)) / 4)
>>>> -       .word   0xdeadbeef
>>>> -       .endr
>>>> +       .fill   ((\size - (. - \sym)) / 4), 4, 0xdeadbeef
>>>>  .endm
>>>>
>>>>         .align  6
>>>> @@ -526,7 +519,10 @@ cmpxchg_stw:
>>>>  cmpxchg_ret:
>>>>         ret
>>>>
>>>> -       kuser_pad __kuser_cmpxchg, 64
>>>> +       /* The first 64-byte frame contains the version word, so note
>>>> +          that the first padding entry is based from the start of the kuser
>>>> +          page, instead of __kuser_cmpxchg.  */
>>>> +       kuser_pad __kuser_helper_start, 64
>>>>
>>>>         .globl  __kuser_sigtramp
>>>>  __kuser_sigtramp:
>>>> --
>>> Hi Chung-Lin
>>>
>>> I thought this is our original intention for it.
>>>
>>> First 4 bytes is the __kuser_version and each __kuser function will
>>> have 64 bytes size.
>>>
>>> 0x1000 __kuser_helper_version
>>> 0x1004 __kuser_cmpxchg
>>> 0x1044 __kuser_sigtramp
>>>
>>> Any reason you can't use __kuser_sigtramp @ 0x1044?
>>
>> Well, that's okay as well, as the main place which sets this is the
>> signal frame construction in arch/nios2/kernel/signal.c. The user space
>> is mostly oblivious to the exact location.  You'll need to update it
>> that way if you prefer 0x1044, as it's currently set at 0x1040.
>>
>> I suggested 0x1040 because 64b frames aligned at 64b seemed more
>> intuitive; __kuser_cmpxchg would be a special case.
> 
> I think I will change to 0x1044 in arch/nios2/kernel/signal.c. I can
> submit the fix.
> Do you need to update toolchain for this change?

No, the toolchain is not affected by this change.

Thanks,
Chung-Lin

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