From owner-freebsd-dtrace@freebsd.org Tue Nov 28 00:34:04 2017 Return-Path: Delivered-To: freebsd-dtrace@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 D30DDDEE782; Tue, 28 Nov 2017 00:34:04 +0000 (UTC) (envelope-from jbeich@freebsd.org) Received: from freefall.freebsd.org (freefall.freebsd.org [96.47.72.132]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "freefall.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id B697B6C489; Tue, 28 Nov 2017 00:34:04 +0000 (UTC) (envelope-from jbeich@freebsd.org) Received: by freefall.freebsd.org (Postfix, from userid 1354) id 0AF2F1107D; Tue, 28 Nov 2017 00:34:04 +0000 (UTC) From: Jan Beich To: freebsd-dtrace@freebsd.org, freebsd-toolchain@freebsd.org Subject: dtrace -G vs. -flto Date: Tue, 28 Nov 2017 01:34:00 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: freebsd-dtrace@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: "A discussion list for developers working on DTrace in FreeBSD." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 28 Nov 2017 00:34:04 -0000 I'd like to build www/firefox with both DTrace and LTO support. Both Clang and GCC emit code that dtrace(1) doesn't understand. $ cat main.c #include #include int main() { DTRACE_PROBE(test, foo); sleep(300); return 0; } $ cat test.d provider test { probe foo(); }; $ clang50 -flto -c main.c $ dtrace -G -s test.d main.o dtrace: failed to link script test: invalid file type: main.o $ file main.o main.o: LLVM IR bitcode $ gcc7 -flto -c main.c $ dtrace -G -s test.d main.o dtrace: failed to link script test: No probe sites found for declared provider $ file main.o main.o: ELF 64-bit LSB relocatable, x86-64, version 1 (FreeBSD), not stripped -- $ uname -a FreeBSD ... 12.0-CURRENT #0 r325899M ... amd64 From owner-freebsd-dtrace@freebsd.org Tue Nov 28 01:50:23 2017 Return-Path: Delivered-To: freebsd-dtrace@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 C238DDF1B9B; Tue, 28 Nov 2017 01:50:23 +0000 (UTC) (envelope-from markjdb@gmail.com) Received: from mail-pl0-x22c.google.com (mail-pl0-x22c.google.com [IPv6:2607:f8b0:400e:c01::22c]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 914C76F893; Tue, 28 Nov 2017 01:50:23 +0000 (UTC) (envelope-from markjdb@gmail.com) Received: by mail-pl0-x22c.google.com with SMTP id f6so9662861pln.12; Mon, 27 Nov 2017 17:50:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=YOMGtPuIwWJO6pWlpZIe/byIjfZUNUtjAZETvEPwq9w=; b=aKdm4N0xlbc9Bz/IMsg9AVxrnTTsCrV0iCB6+vmki/fPBGvoJwRJrZ8OLSXyYCsjKG /1Edsg2ToD6o5jRmw/r1iroCT5dSworzLdBWKObiDRLUgWnhz65oAP5gaOGZjJjC1kmC vldhFiZ9xjWLBKw3jRWwDQYLpkuOwWrk0EccVf3bbEpRNHZVN3CBkpGqWqPaSo3F2YMg Ooz6KsdxtclGKMPA9pku+m9iQqScicBgMwj66D6XyJe9ugdYX7d472WtAl7UZu69y1km jYtTiBsSg11a/P1fYne1r53K4ej3nosjy61NqMPHnMS8+d3XrrFjuNlwsvwn4YQVTlDK +pmw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=YOMGtPuIwWJO6pWlpZIe/byIjfZUNUtjAZETvEPwq9w=; b=N6GO8udYSnfc1WIGhLT8f+IXtUVrqz+E+3YeA1FIElAPZRhuEkcAqYD98/xW7E9x+S /8vq3yYxgiVueGqIZ8tbBpAbRoU6kuRCbBhlMVN/PPGrsS+B+tW2X1PYkWj8tKQXb7qa COK7P4sfT7MXJwsbjlsMwZEt7XWm5aA7sZXGjMCHJVPSGmocbohrEjXGk2J7lNB6L7/A qKvlSZW/L/IAbHz0+aCLIrkdai4OenW1zQ7+k5mNp+Sj98TcThXcarC1A/8+sS0QU7T0 5RYujbN7meKQfn1e52Fx0UxXB/x6viPEJajueB/xQ6N3vh9O6Jw2WMk2+/ilv8hzoJzd 8CUQ== X-Gm-Message-State: AJaThX5f1hL1DTU2akk43HnkkgHYXeQp02f0vRU2+W52smcFVEuZDE20 yeFTOqp0mV718g043pA4gkIXsQ== X-Google-Smtp-Source: AGs4zMZqjxxj9/y9MKwsR5p/nVG1cpRq7qSSZjTk0rojsMur1m1XXg9a084MoyCuOLbI2IjvQBflGg== X-Received: by 10.159.240.134 with SMTP id p6mr20690364plr.344.1511833822362; Mon, 27 Nov 2017 17:50:22 -0800 (PST) Received: from raichu (toroon0560w-lp140-01-69-159-38-22.dsl.bell.ca. [69.159.38.22]) by smtp.gmail.com with ESMTPSA id v1sm17367214pgt.87.2017.11.27.17.50.20 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 27 Nov 2017 17:50:21 -0800 (PST) Sender: Mark Johnston Date: Mon, 27 Nov 2017 20:50:16 -0500 From: Mark Johnston To: Jan Beich Cc: freebsd-dtrace@freebsd.org, freebsd-toolchain@freebsd.org Subject: Re: dtrace -G vs. -flto Message-ID: <20171128015016.GA89416@raichu> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) X-BeenThere: freebsd-dtrace@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: "A discussion list for developers working on DTrace in FreeBSD." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 28 Nov 2017 01:50:23 -0000 On Tue, Nov 28, 2017 at 01:34:00AM +0100, Jan Beich wrote: > I'd like to build www/firefox with both DTrace and LTO support. Both > Clang and GCC emit code that dtrace(1) doesn't understand. Unfortunately, both gcc and clang's LTO implementations are completely incompatible with the way that dtrace -G works. clang -flto produces LLVM bitcode files, and gcc -flto produces ELF files with custom sections. dtrace -G works by looking for relocations against symbols named __dtrace_probe_*, and recording and overwriting the relocation address, but the object files generated when using -flto are really only meant for consumption by the static linker. I think it might be possible to implement USDT for clang using LLVM's patchpoint instrinsic, but this would still require some support in the compiler. Anyway, I don't think it'll be possible to reconcile -flto and dtrace -G without substantial work.