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

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Date:	Thu, 22 Jan 2015 17:12:36 +0800
From:	Ley Foon Tan <lftan@...era.com>
To:	Chung-Lin Tang <cltang@...esourcery.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 Thu, Jan 22, 2015 at 5:07 PM, Chung-Lin Tang <cltang@...esourcery.com> wrote:
> 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.
Okay, will fix this.
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