From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:58781)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <andreas.faerber@web.de>) id 1RA2rc-0002aP-1U
	for qemu-devel@nongnu.org; Sat, 01 Oct 2011 12:56:36 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <andreas.faerber@web.de>) id 1RA2ra-0003Zu-RV
	for qemu-devel@nongnu.org; Sat, 01 Oct 2011 12:56:35 -0400
Received: from fmmailgate02.web.de ([217.72.192.227]:44444)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <andreas.faerber@web.de>) id 1RA2ra-0003Zo-Fd
	for qemu-devel@nongnu.org; Sat, 01 Oct 2011 12:56:34 -0400
Message-ID: <4E8745DE.5030007@web.de>
Date: Sat, 01 Oct 2011 18:54:54 +0200
From: =?ISO-8859-15?Q?Andreas_F=E4rber?= <andreas.faerber@web.de>
MIME-Version: 1.0
References: <4E74FC29.1050003@mail.berlios.de>
	<1316289634-18786-6-git-send-email-weil@mail.berlios.de>
In-Reply-To: <1316289634-18786-6-git-send-email-weil@mail.berlios.de>
Content-Type: text/plain; charset=ISO-8859-15
Content-Transfer-Encoding: 7bit
Sender: andreas.faerber@web.de
Subject: Re: [Qemu-devel] [PATCH 6/8] tcg: Add bytecode generator for tcg
 interpreter
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Stefan Weil <weil@mail.berlios.de>
Cc: QEMU Developers <qemu-devel@nongnu.org>

Am 17.09.2011 22:00, schrieb Stefan Weil:
> Unlike other tcg target code generators, this one does not generate
> machine code for some cpu. It generates machine independent bytecode
> which is interpreted later.
>
> This allows running QEMU on any host.
>
> Interpreted bytecode is slower than direct execution of generated
> machine code.
>
> Signed-off-by: Stefan Weil <weil@mail.berlios.de>
[...]
> diff --git a/tcg/bytecode/README b/tcg/bytecode/README
> new file mode 100644
> index 0000000..6fe9755
> --- /dev/null
> +++ b/tcg/bytecode/README
> @@ -0,0 +1,129 @@
> +TCG Interpreter (TCI) - Copyright (c) 2011 Stefan Weil.
> +
> +This file is released under GPL 2 or later.
> +
> +1) Introduction
> +
> +TCG (Tiny Code Generator) is a code generator which translates
> +code fragments ("basic blocks") from target code (any of the
> +targets supported by QEMU) to a code representation which
> +can be run on a host.
> +
> +QEMU can create native code for some hosts (arm, hppa, i386, ia64, ppc, ppc64,
> +s390, sparc, x86_64). For others, unofficial host support was written.
> +
> +By adding a code generator for a virtual machine and using an
> +interpreter for the generated bytecode, it is possible to
> +support (almost) any host.
> +
> +This is what TCI (Tiny Code Interpreter) does.
> +
> +2) Implementation
> +
> +Like each TCG host frontend, TCI implements the code generator in
> +tcg-target.c, tcg-target.h. Both files are in directory tcg/bytecode.
> +
> +The additional file tcg/tci.c adds the interpreter.
> +
> +The bytecode consists of opcodes (same numeric values as those used by
> +TCG), command length and arguments of variable size and number.

While reusing TCG opcode values certainly makes things easy to
implement, have you evaluated using LLVM bitcode as alternative to a
fully custom intermediate code format?

Andreas