From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E1B4E1CF2A4; Tue, 1 Oct 2024 23:09:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727824199; cv=none; b=PmaDQnOx5oJlzIjVTejk5D5t7KbhB1po+vRn1xe53fVZbmsu1EjXOC65MAHOM+fiyS8q9iz6KKZAY7NA/10ZlVm6lpA76CsxWNRscYqMEePe1Fc09A4OPSIQMYIJDMJsn3PjhEejzmUuOuWXPuac1vvOtPVatWCfF+kebAPIh98= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727824199; c=relaxed/simple; bh=pF10SgafKHT8nhP6OVtYlWEK4BQ14Dt6JDhg5N/Pv88=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jlKWGJpalJqNxENHEaP8JfkEKLdMHMNcqBPW/NiUWhSQ21Yi5tUehFL2K6IUJqrI9EinauzfJsaJRhmq5Z9D3Bq1+zRZyOGhy/+/hSclTayxFlBgJJwwA5fBa/n110zWpw6ytwg1ihVw8p5AaksDa6rG2cnFbJ6PCzKJxZ1Bmg8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=L+ttDD8O; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="L+ttDD8O" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1AE14C4CEC6; Tue, 1 Oct 2024 23:09:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1727824198; bh=pF10SgafKHT8nhP6OVtYlWEK4BQ14Dt6JDhg5N/Pv88=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=L+ttDD8O5uI1aAMqhas9wkfV5KUf4Wge0RUaw1QoeV6GZVd5joQMAzvEb9/jnYgxL dXBMl5RckVtmfg1WGCT6GAx5FMrSmxhZuWQE4+l3ea1OHiJySobCWd6/SuP+u68qOl YEEOArrPCW+Z32FwJ+tOu8l1n2X95CJCLhMuKi7iGXWXS1OZdKXQW532xBLcReu1WH xdkGwhEeJ9sodsfmRFORKLv3cnLWnNS1Pm6NAMhtLrLcUIiJGicPQ6u7ZBj4IG0UGo P7apJqUyaltgVcsK9F2gxOWFmTFT6q1E4vnxcaE0v/7Bhmylgn7pSX2jKu1ivuF8w1 zZrHvGZAZFPBw== Date: Tue, 1 Oct 2024 16:09:55 -0700 From: Namhyung Kim To: Ian Rogers Cc: Masami Hiramatsu , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Adrian Hunter , Kan Liang , John Garry , Will Deacon , James Clark , Mike Leach , Leo Yan , Guo Ren , Paul Walmsley , Palmer Dabbelt , Albert Ou , Nick Terrell , Guilherme Amadio , Changbin Du , "Steinar H. Gunderson" , Aditya Gupta , Athira Rajeev , Masahiro Yamada , Huacai Chen , Bibo Mao , Kajol Jain , Anup Patel , Shenlin Liang , Atish Patra , Oliver Upton , Chen Pei , Dima Kogan , Alexander Lobakin , "David S. Miller" , Przemek Kitszel , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Yang Jihong Subject: Re: [PATCH v1 11/11] perf build: Rename PERF_HAVE_DWARF_REGS to PERF_HAVE_LIBDW_REGS Message-ID: References: <20240924160418.1391100-1-irogers@google.com> <20240924160418.1391100-12-irogers@google.com> <20240929113521.9b7e8fd67af154520e2c9d8e@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Sep 30, 2024 at 09:02:36PM -0700, Ian Rogers wrote: > On Sat, Sep 28, 2024 at 7:35 PM Masami Hiramatsu wrote: > > > > On Fri, 27 Sep 2024 11:15:21 -0700 > > Ian Rogers wrote: > > > > > On Fri, Sep 27, 2024 at 10:16 AM Namhyung Kim wrote: > > > > > > > > On Thu, Sep 26, 2024 at 12:55:18PM -0700, Ian Rogers wrote: > > > > > On Thu, Sep 26, 2024 at 12:40 PM Namhyung Kim wrote: > > > > > > > > > > > > On Thu, Sep 26, 2024 at 05:47:16AM -0700, Ian Rogers wrote: > > > > > > > On Wed, Sep 25, 2024 at 8:27 PM Namhyung Kim wrote: > > > > > > > > > > > > > > > > On Tue, Sep 24, 2024 at 09:04:18AM -0700, Ian Rogers wrote: > > > > > > > > > The name dwarf can imply libunwind support, whereas > > > > > > > > > PERF_HAVE_DWARF_REGS is only enabled with libdw support. Rename to > > > > > > > > > make it clearer there is a libdw connection. > > > > > > > > > > > > > > > > While it only covers libdw, I think the idea of this macro is whether > > > > > > > > the arch has register mappings defined in DWARF standard. So I think > > > > > > > > it's better to keep the name for this case. > > > > > > > > > > > > > > How can the dwarf standard exist for an arch but not define registers? > > > > > > > > > > > > I meant it's about the arch code in the perf tools to have the mapping, > > > > > > not the DWARF standard itself. > > > > > > > > > > But we guard those definitions behind having libdw: > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/arch/x86/Makefile?h=perf-tools-next#n3 > > > > > So we only have the regs if libdw is present, not if dwarf is in use > > > > > for libunwind/libdw. Hence wanting to be specific that they are just a > > > > > libdw and not a dwarf thing. Trying to use the regs in libunwind code > > > > > would be broken. That could change but I wanted to make the code clear > > > > > for the way things are at the moment. > > > > > > > > I understand your point but calling it LIBDW_REGS looks unnatural to me. > > > > > > I don't follow. Wouldn't it be unnatural to see PERF_HAVE_DWARF_REGS > > > in libunwind code but you are to some how know that the code only had > > > meaning if libdw was present? I don't like the implication that DWARF > > > means LIBDW as throughout the code it doesn't. I think the name > > > PERF_HAVE_LIBDW_REGS better captures how the code is, makes the code > > > more intention revealing and so readable, etc. > > > > I agree with Namhyung this point. dwarf-regs is defined only by the > > DWARF standard, not libdw only. The standard encode registers by a digit > > number and the dwarf-regs decode the number to actual register name. > > The code is not making a statement about the DWARF standard, take arch/csky: > https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/arch/csky/Makefile?h=perf-tools-next > ``` > # SPDX-License-Identifier: GPL-2.0-only > ifndef NO_DWARF > PERF_HAVE_DWARF_REGS := 1 > endif > ``` > in the patch series NO_DWARF becomes NO_LIBDW, so it is now: > ``` > # SPDX-License-Identifier: GPL-2.0-only > ifndef NO_LIBDW > PERF_HAVE_DWARF_REGS := 1 > endif > ``` > So the Makefile says that PERF_HAVE_DWARF_REGS is dependent on having > NO_LIBDW, that is having libdw implies PERF_HAVE_DWARF_REGS is defined > for csky. I think this is totally fine and we can change the condition later if needed. After all, I don't think it's a big deal. Let's just call DWARF registers DWARF_REGS. :) Thanks, Namhyung > > Dwarf in the code base implies libdw, libunwind and potentially other > dwarf capable things like llvm. If we don't have libdw then NO_LIBDW > will be set and PERF_HAVE_DWARF_REGS won't be set. That is the more > general dwarf thing will not be set because of missing libdw. This > goes contrary to wanting this to be true whenever a dwarf thing is > present - something that reflecting what the standard says would > achieve. > > In the code base right now PERF_HAVE_DWARF_REGS isn't a dwarf > dependent thing, it is a libdw dependent thing, this is why > PERF_HAVE_LIBDW_REGS is a more intention revealing name as it makes > the connection explicit. > > We could change the code so that in Makefile.config we set something like: > ``` > ... > ifndef NO_LIBDW > PERF_HAVE_DWARF := 1 > ... > ``` > and in the arch/.../Makefiles change them to be: > ``` > if PERF_HAVE_DWARF > PERF_HAVE_DWARF_REGS := 1 > endif > ``` > but this is going beyond the clean up this patch series was trying to > achieve. I also don't know of an architecture where dwarf is present > but registers are not, so having a definition for this case feels > redundant. > > Thanks, > Ian > > > Actually, there is a histrical reason I had called it is DWARF. I used to > > use "libdwarf", and switched to "libdw" for required features. So I know > > there are more than 1 implementation of DWARF library, and the libdwarf > > also uses the same operation number because it depends on the same standard. > > > > https://github.com/davea42/libdwarf-code/blob/main/src/lib/libdwarf/dwarf.h#L809 > > > > So I think we'd better keep it call as DWARF_REGS. > > > > Thank you, > > > > > > > > Thanks, > > > Ian > > > > > > > > > -- > > Masami Hiramatsu (Google)