From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sc8-sf-mx1-b.sourceforge.net ([10.3.1.11] helo=sc8-sf-mx1.sourceforge.net) by sc8-sf-list1.sourceforge.net with esmtp (Exim 4.30) id 1CXVyn-0001Zs-1P for user-mode-linux-devel@lists.sourceforge.net; Thu, 25 Nov 2004 18:37:01 -0800 Received: from smtp001.mail.ukl.yahoo.com ([217.12.11.32]) by sc8-sf-mx1.sourceforge.net with smtp (Exim 4.41) id 1CXVym-000098-9J for user-mode-linux-devel@lists.sourceforge.net; Thu, 25 Nov 2004 18:37:00 -0800 From: Blaisorblade Subject: Re: [uml-devel] [Patch 1/1] uml: fix uml-use-sysemu-for-tt.patch References: <4194C43D.6030107@fujitsu-siemens.com> <200411130854.51896.blaisorblade_spam@yahoo.it> <4198FDD7.4090804@fujitsu-siemens.com> In-Reply-To: <4198FDD7.4090804@fujitsu-siemens.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200411260339.41831.blaisorblade_spam@yahoo.it> Sender: user-mode-linux-devel-admin@lists.sourceforge.net Errors-To: user-mode-linux-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Id: The user-mode Linux development list List-Post: List-Help: List-Subscribe: , List-Archive: Date: Fri, 26 Nov 2004 03:39:41 +0100 To: user-mode-linux-devel@lists.sourceforge.net Cc: Bodo Stroesser , Jeff Dike OK, now finally I went studying the patch. On Monday 15 November 2004 20:04, Bodo Stroesser wrote: > Blaisorblade wrote: > > On Friday 12 November 2004 15:10, Bodo Stroesser wrote: > >>From: Bodo Stroesser > >> > >>The patch needs some small corrections: > >>1) local_using_sysemu must be sampled *before* the next > >> ptrace(PTRACE_SYSEMU/SYSCALL) and must stay the same until > >> do_syscall() has been done. Currently it is sampled before do_syscall() > >> and is used after this for ptrace(PTRACE_SYSEMU/SYSCALL). Ok, now I went analizing the code and what you say is correct. In fact, when merging this I just threw in Jeff Dike's incremental. However, to be correct, I must say that in his tree /proc/sysemu was never introduced, so his tree was correct. > >> Even if no > >> problem is visible to the UML user, a single syscall could be executed > >> on the host when switching on sysemu. The result of this then is > >> overwritten by the syscall execution in UML. > >> Since the first event the tracer has to handle is not a syscall, it's > >> enough to initialize local_using_sysemu to 0; > > > > Sorry, what happens if the first signal it gets is a SIGTRAP, and so > > local_using_sysemu is not yet set? If this is impossible, please add a > > comment in the code for this. However, it seems that it can get to the > > SIGTRAP case with tracing == 1. When beginning the procedure, it is 0, > > but it can be changed with the value from is_tracing(task). I've not > > checked if that is zeroed on process creation (i.e. by do_fork() calling > > copy_thread()), but just note that in the code. > OK: Let's summarize: > 1) tracer() is started exactly once. > 2) The first this it does, is starting the first ptraced-process via > clone(). 3) Then it waits until the new process stops. > 4) Since the process will run start_kernel() in kernel space, it is resumed > with PTRACE_CONT. And it has its is_tracing() set to 0 when it is in kernel mode. > Thus, (I've filled in the actual reasoning below). > before having any syscall interception, it needs to get is_tracing() set to 1, so > the process has to stop > itself with a SIGUSR1, giving the tracer an OP_TRACE_OP request. Ok. > After this > local_using_sysemu will be set and the process will be resumed with > PTRACE_SYSCALL or PTRACE_SYSEMU. So, agreed. Yet, for now I'm still disabling TT SYSEMU in the -bb tree, just in case anything else comes up (it does not give a big advantage anyway). I'm also going to merge this in 2.4-bs -- Paolo Giarrusso, aka Blaisorblade Linux registered user n. 292729 http://www.user-mode-linux.org/~blaisorblade ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/ _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel