Subject: [PATCH 3/3] ARM: tegra: make sure the pointer on 4 byte align when THUMB2_KERNEL enabled

From: [email-masked] (Stephen Warren)
Date: Tue, 16 Apr 2013 10:20:11 -0600

On 04/16/2013 08:13 AM, Dave Martin wrote:
> On Mon, Apr 15, 2013 at 04:50:55PM -0600, Stephen Warren wrote:
>> From: Joseph Lo <[email-masked]>
>>
>> When building kernel with CONFIG_THUMB2_KERNEL, the data pointer in the
>> assembly may not on the 4 byte alignment. Then causing a data abort when
>> accessing the pointer. This patch add a ".align" flag in the head of the
>> pointer. And always using 32-bit ADR Thumb instruction to make sure it
>> won't build failure.
>>
>> Signed-off-by: Joseph Lo <[email-masked]>
>> Signed-off-by: Stephen Warren <[email-masked]>
>> ---
>>  arch/arm/mach-tegra/reset-handler.S |    1 +
>>  arch/arm/mach-tegra/sleep.h         |    3 ++-
>>  2 files changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/mach-tegra/reset-handler.S b/arch/arm/mach-tegra/reset-handler.S
>> index e6de88a..519a8c5 100644
>> --- a/arch/arm/mach-tegra/reset-handler.S
>> +++ b/arch/arm/mach-tegra/reset-handler.S
>> @@ -83,6 +83,7 @@ ENDPROC(tegra_resume)
>>  
>>  #ifdef CONFIG_CACHE_L2X0
>>  	.globl	l2x0_saved_regs_addr
>> +	.align
>>  l2x0_saved_regs_addr:
>>  	.long	0
>>  #endif
>> diff --git a/arch/arm/mach-tegra/sleep.h b/arch/arm/mach-tegra/sleep.h
>> index 4ffae54..8e9b6af 100644
>> --- a/arch/arm/mach-tegra/sleep.h
>> +++ b/arch/arm/mach-tegra/sleep.h
>> @@ -92,7 +92,8 @@
>>  
>>  #ifdef CONFIG_CACHE_L2X0
>>  .macro l2_cache_resume, tmp1, tmp2, tmp3, phys_l2x0_saved_regs
>> -	adr	\tmp1, \phys_l2x0_saved_regs
>> + ARM(	adr	\tmp1, \phys_l2x0_saved_regs )
>> + THUMB(	adr.w	\tmp1, \phys_l2x0_saved_regs )
> 
> Can you give an example of the assembler error you get without this?

arch/arm/mach-tegra/reset-handler.S: Assembler messages:
arch/arm/mach-tegra/reset-handler.S:78: Error: invalid immediate for
address calculation (value = 0x00000004)

This is with gcc-4.5.3, as:
GNU assembler (crosstool-NG hg_unknown at 20110628.165246) 2.20.1.20100303

> The target symbol is local and the assembler can see where it is,
> so it should choose the correct variant for the adr instruction
> with no need for the ".w" suffix.
> 
> If not, it could mean that there is a bug in the version of the
> assembler you're using.

True. Switching to the Ubuntu-packaged ARM cross-compiler that ships
with Ubuntu 12.10, I do not see this problem.

Still, many people probably still use older compilers.

> If it's definitely needed, you can append a Thumb-only .w suffix with
> 
> 	W(adr)	\tmp1, \phys_l2x0_saved_regs
> 
> ...which is slightly neater.

Yes, that certainly works too, even without the .align change in
reset-handler.S.

Arnd, Olof, I guess let's drop this once patch from this series, but
apply the other two, and I'll send an updated version of this one patch.
Thanks.