linux-kernel - Re: [PATCH v3 11/12] x86, boot: add fields to support load bzImage and ramdisk high

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Date:	Thu, 22 Nov 2012 13:02:53 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, Rob Landley <rob@...dley.net>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v3 11/12] x86, boot: add fields to support load bzImage
 and ramdisk high

On 11/22/2012 12:50 PM, H. Peter Anvin wrote:
> On 11/22/2012 12:18 PM, Yinghai Lu wrote:
>>>
>>> If we can get the sentinel hack to work that would probably be
>>> useful, but
>>> we need to understand the exact pathology.
>>
>> for kexec bzImage --real-mode-entry, code after setup_header will be
>> executed.
>>
>> so we could clear value before setup_header after copy 16bit section
>> from bzImage...
>>
>> Index: kexec-tools/kexec/arch/i386/kexec-bzImage.c
>> ===================================================================
>> --- kexec-tools.orig/kexec/arch/i386/kexec-bzImage.c
>> +++ kexec-tools/kexec/arch/i386/kexec-bzImage.c
>> @@ -212,6 +212,16 @@ int do_bzImage_load(struct kexec_info *i
>>       setup_size = kern16_size + command_line_len +
>> PURGATORY_CMDLINE_SIZE;
>>       real_mode = xmalloc(setup_size);
>>       memcpy(real_mode, kernel, kern16_size);
>> +    /*
>> +     * clear value before header
>> +     * not not clear value after header, --real-mode-entry
>> +     * need code after header.
>> +     */
>> +    memset(real_mode, 0, 0x1f1);
>> +    if (!real_mode_entry) {
>> +        /* clear value after setup_header  */
>> +        memset((unsigned char *)real_mode + 0x290, 0, kern16_size -
>> 0x290);
>> +    }
>>
>
> You really should move the memset() into the if() clause as well...
> doesn't matter at the moment, but that is the protocol.
>
> The limit is 0x280, not 0x290, or -- better -- you can use the byte at
> 0x201 to get the size.
>

Not doing so would be wrong, in fact.


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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