X-Recipient: archive-cygwin AT delorie DOT com
X-SWARE-Spam-Status: No, hits=-0.9 required=5.0 	tests=AWL,BAYES_00,RCVD_IN_DNSWL_LOW,RCVD_NUMERIC_HELO,SPF_HELO_PASS,SPF_PASS
X-Spam-Check-By: sourceware.org
To: cygwin AT cygwin DOT com
From: Lenik <lenik AT bodz DOT net>
Subject:  Re: Question of the necessity of rebaseall
Date:  Thu, 14 May 2009 09:49:57 +0800
Lines: 34
Message-ID: <guftc9$de2$1@ger.gmane.org>
References:  <gufoof$4ov$1 AT ger DOT gmane DOT org> <4A0B6BE4 DOT 1020905 AT cygwin DOT com> <gufqp0$8jv$1 AT ger DOT gmane DOT org> <4A0B751A DOT 30007 AT cygwin DOT com>
Mime-Version:  1.0
Content-Type:  text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding:  7bit
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1b3pre) Gecko/20090223 Thunderbird/3.0b2
In-Reply-To: <4A0B751A.30007@cygwin.com>
X-IsSubscribed: yes
Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
Precedence: bulk
List-Id: <cygwin.cygwin.com>
List-Unsubscribe: <mailto:cygwin-unsubscribe-archive-cygwin=delorie DOT com AT cygwin DOT com>
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sourceware.org/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com

On 2009-5-14 9:34, Larry Hall (Cygwin) wrote:
> Lenik wrote:
>> On 2009-5-14 8:55, Larry Hall (Cygwin) wrote:
>>> Lenik wrote:
>>>> Imagebase in PE header is something a bit of optional, that means if
>>>> two dlls with same imagebase, the OS kernel will automaticly relocate
>>>> one of them, to put them in different virtual spaces. So, rebase
>>>> should be a utility for optimizing the overall start-up speed, to
>>>> reduce avoidable relocations, rather then fix start-up errors.
>>>>
>>>> Any idea?
>>>
>>> cygwin1.dll cannot be relocated if the fork semantics are to work. So
>>> while what you say above is true for apps in general, it's not true for
>>> Cygwin apps.
>>>
>>
>> I can't figure out how fork will break the relocation, for libraries
>> have been loaded, they're already relocated before invoke into fork,
>> and for libraries haven't been loaded, they don't need to share memory
>> after new processes created by fork.
>
> You have it backwards. Forking doesn't break the relocation. Relocation
> breaks forking. cygwin1.dll needs to have a very special memory layout to
> implement the fork semantics in Win32. If this memory layout is disrupted,
> fork breaks. Relocating cygwin1.dll disrupts the required memory layout.
> 'rebaseall' does its best to locate all Cygwin DLLs that it knows of
> into a layout that avoids collisions. This maintains the required
> memory layout so fork can do its job.
>
Could you explain in more detail? I can't find any document about this 
special memory layout.

Thanks


--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/