From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1Kix1I-0003Dx-Lg
	for qemu-devel@nongnu.org; Thu, 25 Sep 2008 16:01:00 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1Kix1F-0003Dl-92
	for qemu-devel@nongnu.org; Thu, 25 Sep 2008 16:00:59 -0400
Received: from [199.232.76.173] (port=32960 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1Kix1F-0003Di-1y
	for qemu-devel@nongnu.org; Thu, 25 Sep 2008 16:00:57 -0400
Received: from mail-gx0-f19.google.com ([209.85.217.19]:49208)
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <anthony@codemonkey.ws>) id 1Kix1E-0001Cy-Kr
	for qemu-devel@nongnu.org; Thu, 25 Sep 2008 16:00:56 -0400
Received: by gxk12 with SMTP id 12so8015662gxk.10
	for <qemu-devel@nongnu.org>; Thu, 25 Sep 2008 13:00:56 -0700 (PDT)
Message-ID: <48DBEDBC.80400@codemonkey.ws>
Date: Thu, 25 Sep 2008 14:59:56 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [5274] Add signed versions of save/load functions
References: <E1KgxRs-0002UK-Ch@cvs.savannah.gnu.org>
In-Reply-To: <E1KgxRs-0002UK-Ch@cvs.savannah.gnu.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org, Blue Swirl <blauwirbel@gmail.com>

Blue Swirl wrote:
> -int qemu_get_byte(QEMUFile *f)
> +int8_t qemu_get_byte(QEMUFile *f)
>  {
>      if (f->buf_index >= f->buf_size) {
>          qemu_fill_buffer(f);
> @@ -6329,13 +6329,13 @@
>      return pos;
>  }
>   

So this is the problem.  While qemu_get_byte() returns an int, it 
returns f->buf[pos] and buf is a uint8_t *.  This means that it will 
always return a positive number whereas the new qemu_get_byte() may 
return a negative number.

When dealing with something like qemu_get_be32(), where you're shifting 
qemu_get_byte(), the int8_t is going to get promoted to an int and when 
the int8_t is negative, the result is that the combination is an OR of 
0xFFFFFFFX instead of 0x000000FX.

Which leads me to wonder, how much did you test this changeset?  Because 
I don't think any save/restore could possibly have worked.  Perhaps we 
should revert the whole patchset until it's a bit more flushed out?  I'm 
concerned that integer promotion isn't taken into account in a number of 
places.

Regards,

Anthony Liguori