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 BA8211CFECF; Wed, 2 Oct 2024 13:56:24 +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=1727877384; cv=none; b=a69xDe3/6csKGuJzQmUcbljlMAAAMCba9ckBtu9u27i+EEDo5EWgL0qhPkihby8u/0Hf3brbO58l/AZfiSuniwVn94wOQCFJ/CWkPfRNgVj9oSl5ObQb1Qu99SHy6oj4ZjTUomSSUYTsNkOStKYG8m4a+QINMWs28qB9KEnstoU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727877384; c=relaxed/simple; bh=W+h08NQtIKZPp3xXGXyrl4tcVwG5Fobo36b2ZNchd8c=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=IUNDF8KbIynIlYP0iW852FFr6PBhJ0U0jPo3gNzvJhPB5SFL8p+t+wRtSPr18/fIcKbaJwMgrmcmYDTK0VhTfJ8KDGtVySjOS1DC4uy7MjqU2HOfl+OhurT3HNMCQGPQc2yyJg1nIImpX+PZKRL7PqaBjL0Vlqm9haBYbUA0Ew0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=C/TbjPcE; 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="C/TbjPcE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 48293C4CECD; Wed, 2 Oct 2024 13:56:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1727877384; bh=W+h08NQtIKZPp3xXGXyrl4tcVwG5Fobo36b2ZNchd8c=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=C/TbjPcEPnNF6HzVlzY0C+kDKwCDKVn4BT+oVEkC9wS5g9vC3f4EF6Qgzk3Dtg2Kl uUfcDUwNviF37dmK+Z09ekMSHAGce0R7khJF+JjMb8f0uQoXSiLxbK2B0FxDIe0JGs wrOIU6M4PusKMJ/CJN1sov80Ob4LrwsRBlTXjBany6UsxvB9dEWjW20jJf63oo0nwZ +nkvCguOnQeMZKeO/4CVyptHlGzu58mykRJ/i0s6zq3yi949tvM4R/GtEFY8dM/vkF ptkjlGvLr3S/lOz0DSJX1F5yo0e+4JngIHzdS1gb64LxS7McpkXC2c/fdXXK9tSH+3 d3nEwCbmRz9gg== Date: Wed, 2 Oct 2024 22:56:14 +0900 From: Masami Hiramatsu (Google) To: Ian Rogers Cc: Namhyung Kim , 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: <20241002225614.774bdd0742a826557f142d0e@kernel.org> In-Reply-To: References: <20240924160418.1391100-1-irogers@google.com> <20240924160418.1391100-12-irogers@google.com> <20240929113521.9b7e8fd67af154520e2c9d8e@kernel.org> <20241002082859.8821e441024fe873a4301afc@kernel.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Tue, 1 Oct 2024 18:31:43 -0700 Ian Rogers wrote: > On Tue, Oct 1, 2024 at 4:29 PM Masami Hiramatsu wrote: > > > > On Tue, 1 Oct 2024 16:17:34 -0700 > > Ian Rogers wrote: > > > > > On Tue, Oct 1, 2024 at 4:10 PM Namhyung Kim wrote: > > > > > > > > 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. :) > > > > > > The define is called PERF_HAVE_DWARF_REGS, notice the HAVE, but we're > > > not setting it while supporting call-graph dwarf with libunwind. It is > > > actively confusing. > > > > Does libunwind requires the dwarf regs? I think the dwarf regs information > > is only needed for analyzing dwarf register assignment, not stack unwinding. > > So you are saying the #define is guarding a libdw feature? > perf record/report --call-graph=dwarf is supported with either libdw > or libunwind. The dwarf support in the tool may come from more sources > hence wanting in this patch set to be clear what variable is guarding > what. PERF_HAVE_DWARF_REGS is set to 1 for a specific set of > architectures and only when libdw is present. The variable is saying > that libdw supports the notion of registers needed for the #define > HAVE_DWARF_SUPPORT that patch 9 in the series renamed to > HAVE_LIBDW_SUPPORT. So I want the makefile variable > PERF_HAVE_LIBDW_REGS to guard the #define HAVE_LIBDW_SUPPORT, rather > than what is being argued by yourself and Namhyung that the #define > HAVE_LIBDW_SUPPORT be guarded by a variable called > PERF_HAVE_DWARF_REGS and that is only set when NO_LIBDW isn't set. It will be only used with the libdw, but I don't care. "HAVE_DWARF_REG" (internal config, just indicates the arch implemented feature) simply means there is `arch/XXX/util/dwarf-regs.c`. Also the APIs provided by the dwarf-regs.c are still based on DWARF standard, which defines registers by number like DW_OP_reg[0-31]. So the mapping of these suffix number and actual register must be defined for each architecture. That is why I had introduced dwarf-regs.c and call it "dwarf"-regs. Even if the implementation depends on libdw, this dwarf-regs.c is still based on DWARF standard. > We've made a digression into the name dwarf for a reason I can't > fathom, at best it is inconsistent. Having dwarf registers is like > having a bright sun or numeric numbers, it is a truism (playing devils > advocate maybe if there were an ELF file format for postscript we > could have a dwarf specification without registers). Anyway, I'm > trying to connect the dots that libdw support controls the libdw type > variables and defines hence not wanting 10 out of 11 patches applied. Oh, wait, I think we can apply other patches. I just don't like this patch. I think the other patches are good. But this is Thank you, > > Thanks, > Ian > > > Thank you, > > > > > > > > Thanks, > > > Ian > > > > > > > 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) > > > > > > > > > -- > > Masami Hiramatsu (Google) > -- Masami Hiramatsu (Google)