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Re: grub2 comments bug report


From: Vladimir 'φ-coder/phcoder' Serbinenko
Subject: Re: grub2 comments bug report
Date: Fri, 22 Jan 2016 10:24:19 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.5.0

On 13.01.2016 08:46, Andrei Borzenkov wrote:
> 13.01.2016 10:26, Minyoung Go пишет:
>> *Dear GNU Grub Members.*
>> I found weired comments at <Grub>/grub-core/boot/i386/pc/boot.S. Comments
>> in Line 221, 222 is "ljmp to the next instruction because some bogus BIOSes
>> jump to 07C0:0000 instead of 0000:7C00.". However, "ljmp    $0,
>> $real_start" is no longer pointing to adsolute address. This comments were
>> written at version 1.98, when "$real_start" point to adsolute address with
>> ABS macro. Therefore I think this comments should be changed. Below is my
>> idea to change that comments.
>>
> 
> You patch removes the most important information in this comment - why
> this instruction is needed at all.
> 
ljmp is still pointing to absolute address and ABS just wasn't necessary.

disassembly shows:
    7c74:       ea 79 7c 00 00          ljmp   $0x0,$0x7c79
You can see 0000:7c79 baked in
>>
>> diff --git a/grub-core/boot/i386/pc/boot.S
>> b/grub-core/boot/i386/pc/boot.S
>>
>> index 2bd0b2d..378f960
>> 100644
>> ---
>> a/grub-core/boot/i386/pc/boot.S
>> +++
>> b/grub-core/boot/i386/pc/boot.S
>> @@ -221,8 +221,7 @@
>> boot_drive_check:
>>          movb    $0x80,
>> %dl
>>  1:
>>
>>
>> /*
>> -        * ljmp to the next instruction because some bogus
>> BIOSes
>> -        * jump to 07C0:0000 instead of
>> 0000:7C00.
>> +        * ljmp to the next
>> instruction
>>
>> */
>>         ljmp    $0, $real_start
>>
>>
>> I will be looking forward to your reply. Thank you.
>>
>> *Best Regard, Minyoung Go.*
>> Email : address@hidden
>>
> 
> 
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