From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <corinna-cygwin@cygwin.com>
Received: from mout.kundenserver.de (mout.kundenserver.de [217.72.192.75])
 by sourceware.org (Postfix) with ESMTPS id 826193856DFD
 for <cygwin@cygwin.com>; Mon,  4 Jul 2022 08:19:45 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 826193856DFD
Authentication-Results: sourceware.org;
 dmarc=fail (p=none dis=none) header.from=cygwin.com
Authentication-Results: sourceware.org; spf=fail smtp.mailfrom=cygwin.com
Received: from calimero.vinschen.de ([24.134.7.25]) by
 mrelayeu.kundenserver.de (mreue109 [212.227.15.183]) with ESMTPSA (Nemesis)
 id 1M1HmG-1o9w0A0NVi-002pJG for <cygwin@cygwin.com>; Mon, 04 Jul 2022
 10:19:44 +0200
Received: by calimero.vinschen.de (Postfix, from userid 500)
 id 4F464A80BE3; Mon,  4 Jul 2022 10:19:43 +0200 (CEST)
Date: Mon, 4 Jul 2022 10:19:43 +0200
From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: mmap failing with MAP_FIXED
Message-ID: <YsKin3kIuaUsmJXE@calimero.vinschen.de>
Reply-To: cygwin@cygwin.com
Mail-Followup-To: cygwin@cygwin.com
References: <000001d88d68$4d5a7a40$e80f6ec0$@cl.cam.ac.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <000001d88d68$4d5a7a40$e80f6ec0$@cl.cam.ac.uk>
X-Provags-ID: V03:K1:PzlB+wfoU/VPi+/SvB91rlsTZNuN3XJ/glpZ0zNxUWog5qpGhdY
 72vFv9FsDs/PoFNXvS5PbLlpeaaufVrWGRyjf0vBfNsfrktUHpXGwho6Wru8DaqvmUkMyEE
 SMkjytLzjt1N2eKbL5Na378ATJV32+R8ZtoaDHDb/1qVQoBUTMojKxRD/WgeCEz5IUEPA6c
 o86+jkO8gr9Z8HP6UjfXQ==
X-UI-Out-Filterresults: notjunk:1;V03:K0:6sJsmhK2amg=:c8DabZaqf90L9g6wKAJv/1
 KCMqqWHPpBC/MtECYHKttSlcnxbLz0Qzx14tzGTo4+ziBjhv5Q0vsxvvimu9HmcwXAcFDFogR
 VD0OmG7hLII9YiaT5OdmYZaYXPW8Zca/MKNAY+D6dUYR6TK1rSrzY3ViXoWB+ohRw7CyNUFHK
 +f7BXKkBeojlcBvYj9kWjG6s8qrhZ4K2UVLWRA8tRzp0qIOBeE5dmD0ys9r2jMrqaGTCuSRa0
 90Kyjge8YQt/kUWDoAghSH0Eyg/NnEpRxIsyz5Cyv3DD4Gw9FQYlAEB3s+Xs2BLLFbPGz4c9l
 FMIw/2IhyihEM8V6wGm+Qfl+h43YgDyYA4tqsdQF2xqnqH6N5/WENJoExZkeTHP2mBkyepcsQ
 4LQOYsvksrRjDPb8HdEXYqOR5+MdrRkAgB65ADezyF2sKavH03KyIZd++ZTF12vXGLZ1DTS17
 Zb8hX7EQZsjAcQZlql1e2waIFsAIlxXtT2rTo4sJ0Z3VzOU5hDpSXtDgLh/iEQz8xrG+ZFJO2
 uf+SegciM5Hb6Z6F+QOk589QkQ3krV/yH546lbqKavW9+bJASBRpM9s25HhWb36Nk6VOQNhDN
 JQtwnYyWsofOR874bsnj0/L74H2R8gy9CYz8/ZV8iumcz7IaeQ00UNyMSMWUybPf0lZV8BK3W
 pV9JXJyO89VHez8N+2Volvqt2xtL8gK/hh7IUTrzY/W65muh9GYmb1VZMy3GxxA/Fggpg8VVj
 X1cjgE0RvY+KjCPHfWlUKRTBJ4Q8Lz01QkI3ZqUcn6N9apyF5gJLWad4RtE=
X-Spam-Status: No, score=-94.8 required=5.0 tests=BAYES_00,
 GOOD_FROM_CORINNA_CYGWIN, KAM_DMARC_NONE, KAM_DMARC_STATUS, RCVD_IN_DNSWL_NONE,
 SPF_FAIL, SPF_HELO_NONE, TXREP,
 T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
 server2.sourceware.org
X-BeenThere: cygwin@cygwin.com
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe: <https://cygwin.com/mailman/options/cygwin>,
 <mailto:cygwin-request@cygwin.com?subject=unsubscribe>
List-Archive: <https://cygwin.com/pipermail/cygwin/>
List-Post: <mailto:cygwin@cygwin.com>
List-Help: <mailto:cygwin-request@cygwin.com?subject=help>
List-Subscribe: <https://cygwin.com/mailman/listinfo/cygwin>,
 <mailto:cygwin-request@cygwin.com?subject=subscribe>
X-List-Received-Date: Mon, 04 Jul 2022 08:19:46 -0000

On Jul  1 17:33, David Allsopp wrote:
> This program fails at the second mmap call with EINVAL:
> 
>   #include <stdio.h>
>   #include <sys/mman.h>
>   #include <error.h>
> 
>   int main (void) {
>     void * mem;
>     /* Reserve 256MB address space for the minor heaps */
>     mem = mmap(0, 268439552, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>     if (mem == MAP_FAILED)
>       error(1, 0, "Reservation failed");
>     /* Commit the first 2MB heap */
>     if (mmap(mem, 2097152, PROT_READ | PROT_WRITE, MAP_PRIVATE |
> MAP_ANONYMOUS | MAP_FIXED, -1, 0) == MAP_FAILED)
>       error(1, 0, "Commit failed");
>   }
> 
> Is this something that's expected to fail for Cygwin, or a bug?

Depends on the point of view, I guess.  PROT_NONE pages are not just
reserved pages in the Windows sense.  mmap'ed pages are always commited
and PROT_NONE is just a page protection.  Using mmap to change the page
protection of already commited memory is not implemented.  To change
this, use mprotect.


Corinna