linux-kernel - Re: [PATCH] x86: Remove excess calculations for heap_end

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Date:	Fri, 26 Dec 2014 09:04:51 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alexander Kuleshov <kuleshovmail@...il.com>,
	Jeremiah Mahler <jmmahler@...il.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Remove excess calculations for heap_end_ptr

Yes, the -512 is not related to STACK_SIZE, so this patch is wrong.  NAK.

On December 26, 2014 9:03:38 AM PST, Alexander Kuleshov <kuleshovmail@...il.com> wrote:
>Yes, you're right,
>
>At first i thought that it is just typo, and right after that i
>thought about this case when somebody will change STACK_SIZE
>
>2014-12-26 20:35 GMT+06:00 Jeremiah Mahler <jmmahler@...il.com>:
>> Alexander,
>>
>> On Fri, Dec 26, 2014 at 06:22:42PM +0600, Alexander Kuleshov wrote:
>>> heap_end_ptr default value defined as _end+STACK_SZE-512, but
>>                                             STACK_SIZE
>>
>>> STACK_SIZE is already 512.
>>>
>>> Signed-off-by: Alexander Kuleshov <kuleshovmail@...il.com>
>>> ---
>>>  arch/x86/boot/header.S | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
>>> index 16ef025..c69b870 100644
>>> --- a/arch/x86/boot/header.S
>>> +++ b/arch/x86/boot/header.S
>>> @@ -342,7 +342,7 @@ ramdisk_size:     .long   0               # its
>size in bytes
>>>  bootsect_kludge:
>>>               .long   0               # obsolete
>>>
>>> -heap_end_ptr:        .word   _end+STACK_SIZE-512
>>> +heap_end_ptr:        .word   _end
>>>                                       # (Header version 0x0201 or
>later)
>>>                                       # space from here (exclusive)
>down to
>>>                                       # end of setup code can be
>used by setup
>>
>> So right now STACK_SIZE happens to be 512 so STACK_SIZE-512 is zero.
>> What happens if someone changes the size of STACK_SIZE?
>>
>> This change doesn't fix any problem right now and creates potential
>> problems in the future.
>>
>>> --
>>> 2.2.1.201.gbbcefff
>>>
>>> --
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>>
>> --
>> - Jeremiah Mahler

-- 
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