From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=44688 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Ocneg-0003dt-C4 for qemu-devel@nongnu.org; Sat, 24 Jul 2010 18:57:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1Ocnef-0002HG-6O for qemu-devel@nongnu.org; Sat, 24 Jul 2010 18:57:18 -0400 Received: from hall.aurel32.net ([88.191.82.174]:44328) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1Ocnee-0002HA-UO for qemu-devel@nongnu.org; Sat, 24 Jul 2010 18:57:17 -0400 Date: Sun, 25 Jul 2010 00:57:15 +0200 From: Aurelien Jarno Subject: Re: [Qemu-devel] Question on save_globals() in TCG Message-ID: <20100724225715.GE7190@ohm.aurel32.net> References: <20100723175353.GB22478@hall.aurel32.net> <20100724024957.GC22478@hall.aurel32.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jun Koi Cc: qemu-devel@nongnu.org On Sun, Jul 25, 2010 at 01:58:51AM +0900, Jun Koi wrote: > On Sat, Jul 24, 2010 at 11:49 AM, Aurelien Jarno wrote: > > On Sat, Jul 24, 2010 at 09:35:44AM +0900, Jun Koi wrote: > >> On Sat, Jul 24, 2010 at 2:53 AM, Aurelien Jarno wrote: > >> > On Fri, Jul 23, 2010 at 08:59:54PM +0900, Jun Koi wrote: > >> >> Hi, > >> >> > >> >> I am looking at the save_globals() of TCG code, and it seems this > >> >> function saves regular registers like EAX, ..., EDI back to CPU state. > >> >> > >> >> But I am not sure if it also saves value of other registers, like > >> >> EFlags, Segments, CR*, DR*, ... (?) > >> >> From what I saw, it doesnt seem to do so. Is it correct? > >> >> > >> > > >> > save_globals() is run before calling a function that can trigger a CPU > >> > exception, to make sure that in that case all TCG variables are synced > >> > with the CPU state. > >> > >> Is it correct? I always assume that save_globals() is also called at > >> end of each block. > > > > Correct also here. > > > >> > > >> > Given the CPU state only uses "normal" registers, there is no need to > >> > save the other registers. > >> > >> Why do you say that CPU state includes only normal registers, given > >> that, like on x86, CPUState has also segs[], cr[] and dr[]? > >> > >> > >> > >> Another question: if save_globals() only saves regular registers, > >> where Qemu saves other registers  like segs[], cr[]? Or do they always > >> sync, all the time? > > > > It's actually the same question. You are mixing host and target > > registers. save_globals() only saves "normal" host registers. Host > > registers can then contain whatever registers from the target, and > > more precisely the one declared as globals. > > > > > >> Finally, how about Eflags? I remember that Eflags is "lazy sync", but > >> does it sync at end of each block? > >> > > > > It's the same. Eflags are actually stored in a lazy way in cc_* > > globals. They are therefore synced with save_globals(). > > This is very helpful, thanks! > > Another question: as far as I can see in the code, most context is > always synced, all the time. One exception is Eflags, which is only > synced at the end of block. > Is there other lazy synced context, besides EFLAGS? It depends on the target, some of ones are also syncing the program counter lazily. -- Aurelien Jarno GPG: 1024D/F1BCDB73 aurelien@aurel32.net http://www.aurel32.net