Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760646AbZCYLlv (ORCPT ); Wed, 25 Mar 2009 07:41:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760634AbZCYLlj (ORCPT ); Wed, 25 Mar 2009 07:41:39 -0400 Received: from mail-ew0-f165.google.com ([209.85.219.165]:34139 "EHLO mail-ew0-f165.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760622AbZCYLlh (ORCPT ); Wed, 25 Mar 2009 07:41:37 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=ckCuVjQG21KGlcdnYNl5h23zq++rPydBNmQeHfGpFMaVPEgRw9N4qd7LNjoB/QSmVN j92HCFkFJFfstq2VPIFSelIDMwZvGDr9d+9GryCxtiHglFfOczOijR/kNdsBlNiqbiv1 GzL46zy+8EBxLDjS/LUrrzn+pZ9sNF0EzXJmg= Date: Wed, 25 Mar 2009 12:41:31 +0100 From: Frederic Weisbecker To: Russell King - ARM Linux Cc: Abhishek Sagar , Tim Bird , linux-arm-kernel , linux kernel , Steven Rostedt , Ingo Molnar , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Subject: Re: Anyone working on ftrace function graph support on ARM? Message-ID: <20090325114129.GA5976@nowhere> References: <49C936CA.8070800@am.sony.com> <20090324213618.GC5975@nowhere> <49C95EAF.7030901@gmail.com> <20090324224857.GE5975@nowhere> <20090325084248.GF4697@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090325084248.GF4697@n2100.arm.linux.org.uk> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1792 Lines: 36 On Wed, Mar 25, 2009 at 08:42:48AM +0000, Russell King - ARM Linux wrote: > On Tue, Mar 24, 2009 at 11:48:58PM +0100, Frederic Weisbecker wrote: > > On Tue, Mar 24, 2009 at 06:29:03PM -0400, Abhishek Sagar wrote: > > > Instead of just restoring the old backed-up args, lr can be fixed up > > > inside the entry hook to point to the return hook. So when the traced > > > function returns, it actually returns to the return hook (where we can > > > restore the original return address). This means that > > > -finstrument-functions is not required at all. This is analogous to how > > > kretprobes work. The only difference here is that instead of planting a > > > kprobe at the function entry and redirecting the function return to the > > > profiling exit routine, we can use mcount. This is slightly more > > > complicated to implement but can be a very efficient alternative to > > > kretprobes. > > > -- > > > Abhishek > > > > > > > Indeed, you need to override lr, that even the only solution. > > I was still thinking in an x86 way with its on stack return address. > > As pointed out in my previous mail, identifying where on the stack the > return address is stored is only possible for OABI with frame pointers. > > EABI will probably be possible with the stack unwinding code, but it > probably won't be cheap. The EABI unwinder is scheduled for merging > during the present now-open merge window. Hm, if I'm not wrong, the function tracer already depends on frame pointer, this is necessary to retrieve the parent of the caller. -- 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/