Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757726AbYLPWWt (ORCPT ); Tue, 16 Dec 2008 17:22:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752540AbYLPWWg (ORCPT ); Tue, 16 Dec 2008 17:22:36 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:56944 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751671AbYLPWWf (ORCPT ); Tue, 16 Dec 2008 17:22:35 -0500 Date: Tue, 16 Dec 2008 23:22:03 +0100 From: Ingo Molnar To: =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker Cc: Vladislav Bolkhovitin , Steven Rostedt , Sam Ravnborg , linux-scsi@vger.kernel.org, James Bottomley , Andrew Morton , FUJITA Tomonori , Mike Christie , Jeff Garzik , Boaz Harrosh , Linus Torvalds , linux-kernel@vger.kernel.org, scst-devel@lists.sourceforge.net, Bart Van Assche , "Nicholas A. Bellinger" Subject: Re: [PATCH][RFC 2/23]: SCST core Message-ID: <20081216222203.GI14787@elte.hu> References: <49400ACD.3070502@vlnb.net> <20081210191213.GA15273@uranus.ravnborg.org> <49414DBE.6070801@vlnb.net> <20081211210917.GB27010@uranus.ravnborg.org> <4942BA85.3070408@vlnb.net> <1229118607.24995.18.camel@localhost.localdomain> <4943CAAB.4050008@vlnb.net> <20081216214926.GU14787@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Fr?d?ric Weisbecker wrote: > 2008/12/16 Ingo Molnar : > > > > * Fr?d?ric Weisbecker wrote: > > > >> > All the above functionality is almost what we need. The only thing > >> > left, which I forgot to mention, is possibility to log also functions > >> > return value on exit. This is what TRACE_EXIT_RES() in SCST does. Is > >> > it possible to add those? > >> > >> I want to add that on the function graph tracer. That can be done pretty > >> easily. The only problem comes with the type of the return value. Would > >> this tracer be supposed to always return a 64 bits value regardless of > >> the real typ of the value? There would be some pointless bytes on most > >> return values. I don't know how to proceed for this problem. > > > > Things like mov ...,%eax are zero-extend so they'll zap the high 32 bits. > > > That's right, but the problem occurs under 32 bits. The return values > for 64 bits are in eax and edx. And most of the time, the high part > (edx) will be junk. for wider types i'd suggest to just print the low bits. Most of the interesting return types fit into machine word. > > The real problem are byte return values generated via things like: > > > > movb $1, %al > > > > those wont zero-extend, so you could get garbage in the output. One > > approach would be to try a quick hack just to see how common a problem > > this is. > > > Yes, I will try something. > > > We could extract the return type from the debuginfo, hash it in a > > read-mostly table and then look it up, but that seems complex both in > > terms of build overhead and in terms of runtime overhead. > > I thought about it too and as you say it's rather complex. And thinking > about non primitive types (like pid_t....) that would require a second > pass of analysis to retrieve the corresponding primitive... structure returns would be rather evil to handle, agreed. Unrelated: it would be really nice if we could extend ftrace to trace system calls and their parameters and return values. We used to have that in the latency-tracer in -rt, and it was rather useful. Controlled by a trace_option i guess - and blendable into any of the tracer outputs (function tracer most notably). Explicit calls in the entry.S files would be OK for this - but maybe we can get this via the tricky use of a TIF_ flags as well, to force the code into the ptrace callbacks and then divert it for ftrace's pleasure? Ingo -- 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/