X-Recipient:	archive-cygwin AT delorie DOT com
DKIM-Filter:	OpenDKIM Filter v2.11.0 sourceware.org EA9E1384605A
DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1609535471;
	bh=XpOj03aCUkvLPOdlTuZ7XsX0W6PqTV9J3wdYCMOMiGc=;
	h=To:Subject:Date:List-Id:List-Unsubscribe:List-Archive:List-Post:
	List-Help:List-Subscribe:From:Reply-To:From;
	b=pG212loTjrBLIBl3lgLJSB/YeJQEE3qvX0IL4x6bIL9XPI2QlLk3Wzn1VgrOZzaUS
	dLVu9rXTVb74vTKdG/dEcT+yZuX0DYl5WNgKXy+dvkm6li5+dPU/Ftr8nSPVwVqdOO
	g1kzVGvAAoBOf/6pHUvSExURoltRGEBbu3ejCI2c=
X-Original-To:	cygwin AT cygwin DOT com
Delivered-To:	cygwin AT cygwin DOT com
DMARC-Filter:	OpenDMARC Filter v1.3.2 sourceware.org 4A39638460A2
To:	"cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject:	Segfault when accessing mmaped memory on Cygwin
Message-ID:	<c26a63be-f805-7983-1893-74398ac7b60f@netcologne.de>
Date:	Fri, 1 Jan 2021 22:11:01 +0100
User-Agent:	Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
	Thunderbird/78.6.0
MIME-Version:	1.0
X-Spam-Status:	No, score=-4.7 required=5.0 tests=BAYES_00, DKIM_SIGNED,
	DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, SPF_HELO_NONE,
	SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2
X-Spam-Checker-Version:	SpamAssassin 3.4.2 (2018-09-13) on
	server2.sourceware.org
X-BeenThere:	cygwin AT cygwin DOT com
X-Mailman-Version:	2.1.29
List-Id:	General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Archive:	<https://cygwin.com/pipermail/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe:	<https://cygwin.com/mailman/listinfo/cygwin>,
	<mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From:	Thomas Koenig via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Thomas Koenig <tkoenig AT netcologne DOT de>
Sender:	"Cygwin" <cygwin-bounces AT cygwin DOT com>

Hi,

when trying out uf a certain shared memory allocator would
work on Cygwin, I tried out the sample program below (which
works on Linunx, *BSD, AIX and Solaris) and got a suprising
falure with a segmentation fault at the line

   *i1 = 42;

mmap() had succeeded.

Is this a known issue, and would it be possible to work
around that?

Best regards

	Thomas

#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>

#define NAME "/random_namexxx"

int main()
{

   int fd;
   long pagesize;
   void *p1, *p2;
   volatile int *i1, *i2;
   size_t size1, size2;
   off_t offset;

   pagesize = sysconf (_SC_PAGE_SIZE);
   if (pagesize == -1)
     {
       perror ("sysconf failed");
       exit (EXIT_FAILURE);
     }

   fd = shm_open (NAME, O_CREAT | O_EXCL | O_RDWR,  S_IRUSR | S_IWUSR);
   if (fd == -1)
     {
       perror ("shm_open failed");
       exit (EXIT_FAILURE);
     }
   shm_unlink (NAME);

   offset = 0;
   size1 = pagesize;
   p1 = mmap (NULL, size1, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset);
   if (p1 == MAP_FAILED)
     {
       perror ("mmap 1 failed");
       exit (EXIT_FAILURE);
     }
   printf ("p1 = %p\n", p1);
   ftruncate (fd, size1);
   i1 = p1;
   *i1 = 42;
   size2 = 2 * size1;
   p2 = mmap (NULL, size2, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset);
   if (p2 == MAP_FAILED)
     {
       perror ("mmap 1 failed");
       exit (EXIT_FAILURE);
     }
   printf ("p2 = %p\n", p2);
   i2 = p2;
   ftruncate (fd, size2);
   printf ("%d\n", *i2);
   return 0;
}
--
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple

- Raw text -