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Reply-To: <sbardwell AT lbmsys DOT com>
From: "Steven Bardwell" <SBardwell AT lbmsys DOT com>
To: <cygwin AT cygwin DOT com>
References: <01a801cf1cfa$77957900$66c06b00$@lbmsys.com> <20140129181250 DOT GW2821 AT calimero DOT vinschen DOT de> <52E95786 DOT 8050606 AT gmail DOT com> <20140130095822 DOT GY2821 AT calimero DOT vinschen DOT de>
In-Reply-To: <20140130095822.GY2821@calimero.vinschen.de>
Subject: RE: second call to mmap() results in error
Date: Thu, 30 Jan 2014 07:25:37 -0500
Message-ID: <001801cf1db6$66c47c40$344d74c0$@lbmsys.com>
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> > On 29/01/2014 19:12, Corinna Vinschen wrote:
> > >On Jan 29 09:00, Steven Bardwell wrote:
> > >>My application needs several areas of shared memory, and I am getting
> an
> > >>error ("No such device") on the second call to mmap(). The first call
> works
> > >>fine.
> 
> Sorry guys, but it still works fine for me.  I tried your testcase on W7
> 32, W7 64 in 32 and 64 bit, and on Windows 8.1 64 in 32 and 64 bit.  I
> tried it with Cygwin 1.7.27 and with the latest snapshot.  I'm always
> getting the output "Shared memory initialized" and no error at all.
> 
> 
> Any chance one of you guys could debug this further, by stepping through
> the Cygwin mmap64 function, preferredly using the latest snapshot or,
> a self-built Cygwin DLL from?
> 
> 
> Corinna

I reinstalled Cygwin, rebooted and the error persisted. Running 'gdb' and
stepping through the program showed that the call to mmap() fails for /block1
also -- it is returning an invalid address. This simplification of the program
shows that error on my machine ('Bus error (core dumped)' ) occurs
when it tries to do the memcpy() to the mapped address.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/errno.h>
#include <fcntl.h>
#include <sys/mman.h>

int main()
{
  int shm_fd1;
  char *mmap1;
  shm_fd1 = shm_open("/block1", O_CREAT | O_RDWR, 0666);
  if (shm_fd1 == -1) {
    fprintf(stderr, "Couldn't get fd for block1 (%s)\n", strerror(errno));
    exit(1);
  }
  ftruncate(shm_fd1, 524304);
  mmap1 = mmap(NULL, 524304, PROT_WRITE | PROT_READ, MAP_SHARED, shm_fd1, 0);
  if (mmap1 == (char *)-1) {
    fprintf(stderr, "Couldn't map memory for /block1 (%s)\n", strerror(errno));
    exit(1);
  }
  memcpy(mmap1, "ABCDEF\0", 7);
  fprintf(stdout, mmap1);

  fprintf(stdout, "Shared memory initialized\n");
  exit(0);
}
Steve


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