linux-kernel - Re: [PATCH 1/1] ARM: compressed/head.S: fix _

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Date:   Fri, 19 May 2017 13:41:29 +0000
From:   Patrice CHOTARD <patrice.chotard@...com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
CC:     "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Christophe PRIOUZEAU <christophe.priouzeau@...com>,
        Christophe KERELLO <christophe.kerello@...com>,
        Vikas MANOCHA <vikas.manocha@...com>,
        "Patrick DELAUNAY" <patrick.delaunay@...com>
Subject: Re: [PATCH 1/1] ARM: compressed/head.S: fix __nop macro rept number
 for ARMv7M

Hi Ard

On 05/18/2017 01:16 PM, Ard Biesheuvel wrote:
> On 12 May 2017 at 08:22, Patrice CHOTARD <patrice.chotard@...com> wrote:
>> Hi all
>>
>> It's a gentle reminder to not forgot this patch.
>>
>> Thanks
>>
>> Patrice
>>
>> On 04/25/2017 11:01 AM, patrice.chotard@...com wrote:
>>> From: Patrice Chotard <patrice.chotard@...com>
>>>
>>> In zImage, _magic_sig is located at offset 0x24.
>>> But for ARMv7M architecture which enable CPU_THUMBONLY
>>> and !EFI_STUB kernel flag, _magic_sig is located at offset 0x14
>>>
>>> 00000000  00 46 00 46 00 46 00 46  00 46 00 46 00 46 0f f2  |.F.F.F.F.F.F.F.ò|
>>> 00000010  15 0c 60 47 18 28 6f 01  00 00 00 00 28 5c 0e 00  |..`G.(o.....(\..|
>>> 00000020  01 02 03 04 0f 46 90 46  00 00 00 00 00 00 00 00  |.....F.F........|
>>>
>>> Reproduced with stm32_defconfig with XIP_KERNEL flag disabled.
>>>
>>> To restore correct _magic_sig offset at 0x24, we add 8 additional
>>> "mov r0, r0" instruction.
>>>
>>> Signed-off-by: Patrice Chotard <patrice.chotard@...com>
>>> ---
>>>   arch/arm/boot/compressed/head.S | 3 ++-
>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
>>> index 9150f97..5d9cda3 100644
>>> --- a/arch/arm/boot/compressed/head.S
>>> +++ b/arch/arm/boot/compressed/head.S
>>> @@ -127,7 +127,8 @@
>>>    AR_CLASS(   .arm    )
>>>   start:
>>>                .type   start,#function
>>> -             .rept   7
>>> +   ARM(              .rept   7)
>>> + THUMB(              .rept   15)
>>>
> 
> Could you try using W(mov) instead of mov in the definition of __nop ?

If i use W(mov) instead of mov in __nop macro, i need to add one 
additional "mov r0,r0" in THUMB case as following :


  start:
  		.type	start,#function
  		.rept	7
  		__nop
  		.endr
     ARM(		mov	r0, r0		)
     ARM(		b	1f		)
+ THUMB(		mov	r0, r0		)
   THUMB(		badr	r12, 1f		)
   THUMB(		bx	r12		)

  		.word	_magic_sig	@ Magic numbers to help the loader
  		.word	_magic_start	@ absolute load/run zImage address
  		.word	_magic_end	@ zImage end address
  		.word	0x04030201	@ endianness flag


Which implementation do you prefer ?

Thanks

Patrice