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

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Message-ID: <CANCZXo4LbSrUU_=LuXmrJ3=aC6cvtDD77JVa6Hhe1y5GTNuK5g@mail.gmail.com>
Date:	Fri, 26 Dec 2014 23:03:38 +0600
From:	Alexander Kuleshov <kuleshovmail@...il.com>
To:	Jeremiah Mahler <jmmahler@...il.com>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Remove excess calculations for heap_end_ptr

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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