Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765517AbZDARkl (ORCPT ); Wed, 1 Apr 2009 13:40:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757557AbZDARkb (ORCPT ); Wed, 1 Apr 2009 13:40:31 -0400 Received: from mx2.redhat.com ([66.187.237.31]:34115 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756622AbZDARka (ORCPT ); Wed, 1 Apr 2009 13:40:30 -0400 Message-ID: <49D3A708.9080501@redhat.com> Date: Wed, 01 Apr 2009 13:40:24 -0400 From: Masami Hiramatsu User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Ingo Molnar CC: Arnaldo Carvalho de Melo , Steven Rostedt , Ananth N Mavinakayanahalli , Frederic Weisbecker , Linux Kernel Mailing List , systemtap-ml , Andrew Morton , Jim Keniston Subject: Re: [PATCH -tip 0/4 V3] tracing: kprobe-based event tracer References: <49CC08A2.5030602@redhat.com> <20090401133654.GB18677@elte.hu> <49D37584.50208@redhat.com> <20090401142711.GG18677@elte.hu> In-Reply-To: <20090401142711.GG18677@elte.hu> X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3317 Lines: 94 Ingo Molnar wrote: > * Masami Hiramatsu wrote: > >> Ingo Molnar wrote: >>> * Masami Hiramatsu wrote: >>> >>>> Hi, >>>> >>>> Here are the patches of kprobe-based event tracer for x86, version >>>> 3. Since this feature seems to attract some developers, I'd like >>>> to push these basic patches into -tip tree so that they can easily >>>> play it. >>>> >>>> This version supports only x86(-32/-64) (If someone is interested >>>> in porting this to other architectures, I'd happy to help :)), and >>>> no respawn-able probe support (this would be better to push -mm >>>> tree.) >>>> >>>> This can be applied on the linux-2.6-tip tree. >>> This bit: >>> >>>> Future items: >>>> - Check insertion point safety by using instruction decoder. >>> is i believe a must-fix-before-merge item. >> Hi Ingo, >> >> I agreed. Fortunately, Jim Keniston and I wrote an x86 instruction >> decoder :-) which has been made originally for uprobe andd kprobes >> jump-optimizer. >> >> https://www.redhat.com/archives/utrace-devel/2009-March/msg00031.html > > looks cool. Needs to be put somewhere in arch/x86/lib/, provided as > a generic facility, with a Kconfig variable that says that the > architecture supports it and then the kprobes-tracer could make > immediate use of it, right? Yeah, I'd rather add a safety checker in kprobes-x86 itself, because sometimes it has to fixup instructions modified by previous kprobes. Thanks, >>> The functionality is genuinely useful, and if used dynamically on >>> the host it can be a lot more versatile and a lot more accessible >>> than a KGDB session - but code patching safety is a must-have. >>> >>> It does not have to be a full decoder, just a simplified decoding >>> run that starts from a known function-symbol address, and works its >>> way down in the function looking at instruction boundaries, and >>> figuring out whether the code patching is safe. If it sees anything >>> it cannot deal with it bails out. >> Yeah, that is what I'll do. >> >>> I suspect you could get very good practical results by supporting >>> just a small fraction of the x86 instruction set architecture. If >>> failures to insert a probe safely are printed out in clear terms: >>> >>> Could not insert probe at address 0xc01231234 due to: >>> Unknown instruction: 48 8d 15 db ff ff ff 00 00 00 >>> >>> People will fill in the missing ISA bits quickly :-) >>> >>> And people doing: >>> >>> asm(" .byte 0x00, 0x01, 0x02, 0x03;"); /* hehe, I broke the decoder! */ >>> >>> ... in kernel .text functions will be talked to in private :) >> Aha, that function will get illegal instruction exception :-) even >> without kprobe. > > Not if it's under a never-true (not provable to the compiler) branch > condition but i digress :) > >>> Can you see any fundamental reason why this couldnt be done? >> Nope, because we've done :-) > > Cool :) > > Ingo -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division e-mail: mhiramat@redhat.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/