From owner-freebsd-gecko@freebsd.org Mon Apr 17 21:30:25 2017 Return-Path: Delivered-To: freebsd-gecko@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 9EED6D42E1A; Mon, 17 Apr 2017 21:30:25 +0000 (UTC) (envelope-from gnn@neville-neil.com) Received: from relay4-d.mail.gandi.net (relay4-d.mail.gandi.net [217.70.183.196]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 6052916AF; Mon, 17 Apr 2017 21:30:25 +0000 (UTC) (envelope-from gnn@neville-neil.com) Received: from [172.20.10.2] (unknown [IPv6:2607:fb90:543f:94a3:6989:c931:5891:e05f]) (Authenticated sender: gnn@neville-neil.com) by relay4-d.mail.gandi.net (Postfix) with ESMTPSA id 5DA8C172094; Mon, 17 Apr 2017 23:30:22 +0200 (CEST) From: "George Neville-Neil" To: "Mark Johnston" Cc: "Sevan / Venture37" , "Jan Beich" , freebsd-gecko@freebsd.org, "freebsd-dtrace@freebsd.org" Subject: Re: DTrace issues? Date: Mon, 17 Apr 2017 17:30:20 -0400 Message-ID: In-Reply-To: <20170417212610.GE18960@wkstn-mjohnston.west.isilon.com> References: <3CEE1970-719B-42D1-A95A-FEAD3F375A30@neville-neil.com> <20170212191826.5599A45EA@freefall.freebsd.org> <77416dea-1e9d-4911-b5d0-2ebac227af7e@Spark> <76897620-E958-4AE2-9B6C-062C59526614@neville-neil.com> <20170417212610.GE18960@wkstn-mjohnston.west.isilon.com> MIME-Version: 1.0 Content-Type: text/plain; format=flowed X-Mailer: MailMate (1.9.6r5347) X-BeenThere: freebsd-gecko@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Gecko Rendering Engine issues List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 17 Apr 2017 21:30:25 -0000 On 17 Apr 2017, at 17:26, Mark Johnston wrote: > On Mon, Apr 17, 2017 at 09:28:07PM +0100, Sevan / Venture37 wrote: >> On 17 April 2017 at 20:54, Ryan Stone wrote: >>> On Sat, Apr 15, 2017 at 10:50 AM, George Neville-Neil >>> >>> wrote: >>> >>>> >>>> Can you explain this grief? What is the problem? >>>> >>>> Best, >>>> George >>>> >>> >>> dtrace -G requires the ability to modify the object files in-place >>> before >>> linking. This causes havoc if the objects are in .a archives >>> (dtrace can't >>> read those) or if the objects need to be linked into multiple >>> binaries. It >>> also destroys the ability to do an incremental build, as dtrace -G >>> can't be >>> run on the same object twice. >>> >>> The whole process is really a hack. The build actions done by >>> dtrace >>> should be done by the compiler and linker instead. Getting the >>> linker to >>> support the process would go a long way, as then dtrace -G could be >>> run on >>> individual objects and most of my complaints go away. >> >> Not to detract from the issue with the -G flag, I just wanted to >> highlight that it's used for ELF binaries, until Apple switches away >> from Mach-o, this wont be an issue there (dtrace on OS X does not >> feature the -G flag). > > I think the more significant difference is that Apple has more control > over their toolchain and have modified it to directly implement the > functionality that's overwise implemented by dtrace -G. > > As Ryan pointed out, this functionality really belongs in the static > linker; one more piece of evidence for this is the number of > non-trivial > modifications we've needed to make to dtrace -G to avoid relying on > undocumented behaviour in the Sun link editor, and later, GNU ld 2.17. > Now that FreeBSD is transitioning to lld, we have some opportunity to > implement USDT support in the static linker, and at least one of the > lld > developers seems amenable to proposals along those lines. However, I > don't know of any concrete plans or designs. Seems like something we could discuss in an RFD: https://github.com/opendtrace/rfd Best, George