From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1O72O4-0001iK-AW
	for qemu-devel@nongnu.org; Wed, 28 Apr 2010 04:12:52 -0400
Received: from [140.186.70.92] (port=57672 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1O72O0-0001hJ-Qd
	for qemu-devel@nongnu.org; Wed, 28 Apr 2010 04:12:50 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69)
	(envelope-from <jan.kiszka@siemens.com>) id 1O72Nz-0003Ot-Ds
	for qemu-devel@nongnu.org; Wed, 28 Apr 2010 04:12:48 -0400
Received: from goliath.siemens.de ([192.35.17.28]:23810)
	by eggs.gnu.org with esmtp (Exim 4.69)
	(envelope-from <jan.kiszka@siemens.com>) id 1O72Nz-0003OU-1D
	for qemu-devel@nongnu.org; Wed, 28 Apr 2010 04:12:47 -0400
Message-ID: <4BD7EDFA.9010102@siemens.com>
Date: Wed, 28 Apr 2010 10:12:42 +0200
From: Jan Kiszka <jan.kiszka@siemens.com>
MIME-Version: 1.0
References: <t2pfdaac4d51004272151x36aae777wc4f95d1d9ec0de3a@mail.gmail.com>
In-Reply-To: <t2pfdaac4d51004272151x36aae777wc4f95d1d9ec0de3a@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
Subject: [Qemu-devel] Re: Question on implementatio of GETPC()
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: Jun Koi <junkoi2004@gmail.com>
Cc: qemu-devel@nongnu.org

Jun Koi wrote:
> Hi,
> 
> In x86, GETPC() is implemented as below:
> 
> # define GETPC() ((void *)((unsigned long)__builtin_return_address(0) - 1))
> 
> As I understand, it gets the returned address on the stack, then
> subtract 1 to get back to the above address.
> 
> Imagine we have code like this (pseudo asm code):
> 
> ....
> CALL <relative address>
> <next-insn>
> ....
> 
> When we call GETPC, we get the address of <next-insn>, and subtract 1.
> But the problem is that the CALL insn is more than 1 byte, so how can
> GETPC() gives us the address of the CALL insn above?
> 
> I guess I must misunderstood something here ....

IIRC, the result of GETPC is used for a range check. So you just have to
ensure that it points somewhere into the translated code sequence of the
current target instruction.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux