On Apr 12 13:23, Corinna Vinschen wrote: > On Apr 11 20:25, Christoph Weise wrote: > > Please see below, I provide minimal C code for three separate > > executables, one creates the shm section, another finds it, the third > > removes it. I include also a bash test script that executes the > > routines in order. > > Thanks, > > > Please beware as I removed some checks to reduce > > the length of the code, but it should run ok. The PAGESIZE parameter > > is hardcoded (here 512 bytes). The desired shared mem section size is > > set interactively as input to makeshm, or automatically with the bash > > script. > > Ok, but there are bugs in the code which result in GCC warnings. I > don't know which of them are part of your original code, but they are > really a problem. > > if ((int) -1 == p) > > Don't check a pointer against an int value. It won't work on a 64 bit > platform. Make that > > if ((void *) -1 == p) > > For the same reason, don't use %x to printf a pointer. Use %tx. > > > I can write to the shm section with the second routine when the requested > > section <= 4096 bytes. Otherwise it's not happy. > > The problem is the call to shmget: > > #undef PAGESIZE > #define PAGESIZE 512 > shmid = shmget(key, PAGESIZE, IPC_ALLOC); > > Since you're requesting only 512 bytes, the shared memory segment the > following shmat call returns is only 4K. The shmget call should request > as much memory as it needs so that the OS call is called with the right > view size. > > I re-read the POSIX man page for shmget, and it doesn't mention anything > which would point out that Cygwin's behaviour here is wrong. If anybody > has more information on this, please share them.
On second thought, adjusting Cygwin's behaviour to Linux here is rather trivial. I applied a patch to the git repo and uploaded new developer snapshots (2015-04-12) to https://cygwin.com/snapshots/ You only have to replace the DLL itself, cygserver is not affected by this patch. Please give it a try. Thanks, Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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