linux-kernel - Re: [PATCH]x86_64: build and use GDT on copied compressed kernel

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Message-ID: <m1abw9qkve.fsf@ebiederm.dsl.xmission.com>
Date:	Sun, 13 May 2007 00:48:53 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
Cc:	"Andi Kleen" <ak@...e.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Vivek Goyal" <vgoyal@...ibm.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]x86_64: build and use GDT on copied compressed kernel

"Yinghai Lu" <yhlu.kernel@...il.com> writes:

> On 5/12/07, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>> Overwriting the GDT should be fine because we don't reload the segments,
>> after we overwrite it.  GDT entries are only read when we load segments.
>> Interrupts are disabled so that should not cause a problem.
>>
>> Why do you think the current behaviour is a problem?
>
> just think if GDT should not be overwriten when we are still under
> that GDT setting.
> didn't have chance to test that in HDT or other debug device, when
> setting breaking point after that GDT is overwriten.

It would be interesting to see if you could produce a failure using
that gdt, I don't think you will be able to, even with a debugger.

For data segments we never use that GDT, it is only for the code
segment we use the GDT and that only to get us into 64bit mode.

Eric
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