linux-kernel - Re: [PATCH 3/5] parisc: use new macros for .data.init

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Message-ID: <49FDF282.7010207@gmx.de>
Date:	Sun, 03 May 2009 21:37:38 +0200
From:	Helge Deller <deller@....de>
To:	Sam Ravnborg <sam@...nborg.org>
CC:	Tim Abbott <tabbott@....EDU>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Anders Kaseorg <andersk@....edu>,
	Waseem Daher <wdaher@....edu>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Jeff Arnold <jbarnold@....edu>,
	Kyle McMartin <kyle@...artin.ca>, linux-parisc@...r.kernel.org
Subject: Re: [PATCH 3/5] parisc: use new macros for .data.init_task.

Sam Ravnborg wrote:
> On Sat, May 02, 2009 at 07:13:37AM +0200, Helge Deller wrote:
>> Tim Abbott wrote:
>>> .data.init_task should not need a separate output section; this change
>>> moves it into the .data section.
>>>
>>> Signed-off-by: Tim Abbott <tabbott@....edu>
>>> Cc: Kyle McMartin <kyle@...artin.ca>
>>> Cc: Helge Deller <deller@....de>
>>> Cc: linux-parisc@...r.kernel.org
>>
>> I think this patch is wrong, although it is theoretically correct.
>>
>> IIRC, gcc on hppa is not able to provide an alignment >= 8k, which is
>> why we have done the 16k alignment inside the linker script.
>> So, I think this change will prevent the parisc kernel to boot up.
>> Needs testing.
> 
> The patch does not do much...
> 
>> Helge
>>
>>> ---
>>>  arch/parisc/kernel/init_task.c   |    2 +-
>>>  arch/parisc/kernel/vmlinux.lds.S |   10 ++--------
>>>  2 files changed, 3 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/arch/parisc/kernel/init_task.c b/arch/parisc/kernel/init_task.c
>>> index 1e25a45..8ee17ea 100644
>>> --- a/arch/parisc/kernel/init_task.c
>>> +++ b/arch/parisc/kernel/init_task.c
>>> @@ -48,7 +48,7 @@ EXPORT_SYMBOL(init_mm);
>>>   * "init_task" linker map entry..
>>>   */
>>>  union thread_union init_thread_union
>>> -	__attribute__((aligned(128))) __attribute__((__section__(".data.init_task"))) =
>>> +	__attribute__((aligned(128))) __init_task_data =
>>>  		{ INIT_THREAD_INFO(init_task) };
> This is a simple replacement with a nicer way to say "this belongs to
> the .data.init_task section - no functional difference.
> 
> 
>>>  
>>>  #if PT_NLEVELS == 3
>>> diff --git a/arch/parisc/kernel/vmlinux.lds.S b/arch/parisc/kernel/vmlinux.lds.S
>>> index b5936c9..c8a528d 100644
>>> --- a/arch/parisc/kernel/vmlinux.lds.S
>>> +++ b/arch/parisc/kernel/vmlinux.lds.S
>>> @@ -103,6 +103,8 @@ SECTIONS
>>>  	. = ALIGN(L1_CACHE_BYTES);
>>>  	/* Data */
>>>  	.data : {
>>> +		/* assembler code expects init_task to be 16k aligned */
>>> +		INIT_TASK_DATA(16384)
>>>  		NOSAVE_DATA
>>>  		CACHELINE_ALIGNED_DATA(L1_CACHE_BYTES)
>>>  		DATA_DATA
>>> @@ -133,14 +135,6 @@ SECTIONS
>>>  	}
>>>  	__bss_stop = .;
>>>  
>>> -
>>> -	/* assembler code expects init_task to be 16k aligned */
>>> -	. = ALIGN(16384);
>>> -	/* init_task */
>>> -	.data.init_task : {
>>> -		*(.data.init_task)
>>> -	}
>>> -
> This part moves away from a specific output section to including this in the
> .data output section - with the _same_ alignmnet.
> So the only issue here is that we move init_task before NOSAVE_DATA etc.
> 
> I do not see why you think this changes alignmnet?

Ugh. Of course you are correct. It doesn't change anything.
Patch is OK for me.
I missed the 16384 in INIT_TASK_DATA(16384).

Thanks,
Helge
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