From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 49A70C433F5 for ; Wed, 15 Dec 2021 09:48:17 +0000 (UTC) Received: from localhost ([::1]:49636 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mxQtU-0003iO-4A for qemu-devel@archiver.kernel.org; Wed, 15 Dec 2021 04:48:16 -0500 Received: from eggs.gnu.org ([209.51.188.92]:54788) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mxQrV-00025w-Jp for qemu-devel@nongnu.org; Wed, 15 Dec 2021 04:46:16 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:24703) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mxQrS-0002IF-La for qemu-devel@nongnu.org; Wed, 15 Dec 2021 04:46:12 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639561569; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=7tOVKf/DYoq21pLhevp6W96nq9k4VJbxbjUYZtlNih4=; b=hz2JF8aWCmtsO3NDXmNKDUJ0iYrycqTbyL+W9Q8xuaMESRLq5Z2wjmBMKgGeG/JP07E1nQ ok6u0q3FQGypiiHX418C6y8iuk5tmJzzr4+hQitIYxmVGWunDxHuteCS21GeBEGu/rmoht Hj+0UACpXu88C990dU4jAQLeg0S/aw0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-510-tVPcU7R6O0q_mIRua1z5Og-1; Wed, 15 Dec 2021 04:45:58 -0500 X-MC-Unique: tVPcU7R6O0q_mIRua1z5Og-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BF2AA1006AA8; Wed, 15 Dec 2021 09:45:57 +0000 (UTC) Received: from localhost (unknown [10.39.195.21]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5E13862713; Wed, 15 Dec 2021 09:45:57 +0000 (UTC) Date: Wed, 15 Dec 2021 09:45:56 +0000 From: Stefan Hajnoczi To: Amir Gonnen Subject: Re: Building QEMU as a shared library Message-ID: References: MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="oAY86D2dV/STlk76" Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.719, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "peter.maydell@linaro.org" , "qemu-devel@nongnu.org" , f4bug@amsat.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --oAY86D2dV/STlk76 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Dec 15, 2021 at 08:18:53AM +0000, Amir Gonnen wrote: > Before sending a patch, I would like to check if it's of interest to the = community. >=20 > My goal is to simulate a mixed architecture system. > Today QEMU strongly assumes that the simulated system is a *single archit= ecture*. > Changing this assumption and supporting mixed architecture in QEMU proved= to be > non-trivial and may require significant development effort. Common code s= uch as > TCG and others explicitly include architecture specific header files, for= example. Hi Amir, Simulating heterogenous machines comes up from periodically. So far no one has upstreamed a solution but there is definitely interest. I suggest going ahead and posting the code even if it's not cleaned up. > A possible solution, discussed on https://stackoverflow.com/q/63229262/61= 9493 is to > separate the simulation to multiple processes (as done by Xilinx) and to = use some form > of Interprocess Communication channel between them. > Such solution has several disadvantages: >=20 > - Harder to synchronize simulation between processes > - Performance impact of Interprocess Communication > - Harder to debug, profile and maintain >=20 > Instead, I would like to suggest a new approach we use at Neuroblade to a= chieve this: > Build QEMU as a shared library that can be loaded and used directly in a = larger simulation. > Today we build qemu-system-nios2 shared library and load it from qemu-sys= tem-x86_64 in order > to simulate an x86_64 system that also consists of multiple nios2 cores. > In our simulation, two independent "main" functions are running on differ= ent threads, and > simulation synchronization is reduced to synchronizing threads. >=20 > To achieve this, I needed to do the following changes in QEMU: >=20 > 1. Avoid Glib global context. Use a different context (g_main_context_new= ) for each QEMU instance. > 2. Change meson.build to build QEMU as a shared library (with PIC enabled= for static libraries) > 3. Define a C API for the library and export it (with a -Wl,--version-scr= ipt) >=20 > These changes seem enough for simulating mixed architecture system on a s= ingle process. >=20 > If this approach sounds useful, I'll be happy to send patches. > I'd appreciate if you could provide your feedback! I'm curious how much synchronization and IPC there is between the QEMU shared libraries? I would have guessed that the pain of making communication work efficiently between processes would be less than the pain of solving global state bugs related to shared libraries within a single process. Were there issues with POSIX signal handlers? 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