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Date: Fri, 27 Oct 2000 00:57:01 +0200
From: "J . A . Magallon" <jamagallon@able.es>
To: Marc_Schneider@ers.com
Cc: lkml@dm.ultramaster.com, linux-kernel@vger.kernel.org
Subject: Re: Problem with msgsnd
Message-ID: <20001027005701.A788@werewolf.cps.unizar.es>
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In-Reply-To: <39F84A92.BDCB869C@ers.com>; from Marc_Schneider@ers.com on Thu, Oct 26, 2000 at 17:15:30 +0200
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On Thu, 26 Oct 2000 17:15:30 Marc Schneider wrote:
> lkml@dm.ultramaster.com wrote:
> > 
> > Marc Schneider wrote:
> > >
> > > msgsnd seems to be corrupting memory around the msgbuf pointer.
> > >
> > > for example I have the following code:
> > >
> > > pMsgBuf = malloc(iPacketLen + 4 + 8);
> > > bzero(pMsgBuf, iPacketLen + 4 + 8);
> > > pMsgBuf += 4; /* Build a guard band */
> > >
> > > printf("PMQ:pMsgBuf: %p\n",pMsgBuf);
> > > printf("PMQ:-4: %p\n", *(pMsgBuf-4));
> > >

Silly question: why do you :

printf("PMQ:-4: %p\n", *(pMsgBuf-4));

instead of:
                !!!
printf("PMQ:-4: %d\n", *(pMsgBuf-4));, or whatever applies...(typeof pMsgBuf?)

If you use %p, printf expects a pointer in stack, and depending on type of
pMsgBuf (is a char * ?), *pMsgBuf can be passed as a char (I don't think so,
C passes chars as ints, and I dont remenber any kind of option to modify this)
or a short or an int...

So, perhaps you dont put enough data on stack for a pointer and printf gets
incorrect data (the zero in pMsgBuf plus the return value that stored in rc...).

-- 
Juan Antonio Magallon Lacarta                          mailto:jamagallon@able.es

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