From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EAB9AC64E8A for ; Tue, 1 Dec 2020 04:19:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5C04D206C1 for ; Tue, 1 Dec 2020 04:19:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nifty.com header.i=@nifty.com header.b="TG81yAjY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728291AbgLAETV (ORCPT ); Mon, 30 Nov 2020 23:19:21 -0500 Received: from conssluserg-01.nifty.com ([210.131.2.80]:35489 "EHLO conssluserg-01.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728211AbgLAETU (ORCPT ); Mon, 30 Nov 2020 23:19:20 -0500 Received: from mail-pj1-f52.google.com (mail-pj1-f52.google.com [209.85.216.52]) (authenticated) by conssluserg-01.nifty.com with ESMTP id 0B14IKKj021660; Tue, 1 Dec 2020 13:18:20 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-01.nifty.com 0B14IKKj021660 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1606796300; bh=GMCnYM+voihvO7OPv2mqIVM7rj+QDDQzTVQXG07MvGI=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=TG81yAjY1idEUthd84zQkpIZ3TMytSylasR1ZjbVj2sGLPJizj9QFfC0lncrt1wb2 nyg9FFzi+e7uczvGqm7v2QyC0xbjsdMS/U5/1Q8XwP9a4X8eQi7JjGsqzCFo0whp58 AVz4FtYoFrN6yRT1zgefB9POp6ZHRrRxfGEkhFkl4HMpk7nUGy41PbiEEgQx0L3dt+ nLGBFH5KL2CJePXg2p47vtHqkJISEp9ErmJSUxddSMlPZC7ZPeqscNz1IsgVzL1zhx OAJdU/rFvcb6mWOBmFfoI5b+RwXhC1NKZPCFFUk9RXHwpJ46yoXBEiaIvlrvEU9VIB CUNVpm7gc/+lg== X-Nifty-SrcIP: [209.85.216.52] Received: by mail-pj1-f52.google.com with SMTP id j13so434939pjz.3; Mon, 30 Nov 2020 20:18:20 -0800 (PST) X-Gm-Message-State: AOAM530EcbnmI+ypUVn5nk5fdBFXOrBmlnerc/8D92LDnmSu6Zsn4+XG 0yZrpk4d0YDbnuEZBwVfZ4E8imFF0mksPb6DUNQ= X-Google-Smtp-Source: ABdhPJzJYk+YCcfYVbfJ2uBjcUqgstH4E28KmqXmlb16hsg5sT1z+ueAiUcjeCgR3pq73cDye9tk1+GC0wtFJxzBHdg= X-Received: by 2002:a17:90a:5905:: with SMTP id k5mr792484pji.198.1606796299598; Mon, 30 Nov 2020 20:18:19 -0800 (PST) MIME-Version: 1.0 References: <20201104005343.4192504-1-ndesaulniers@google.com> <20201104005343.4192504-4-ndesaulniers@google.com> In-Reply-To: From: Masahiro Yamada Date: Tue, 1 Dec 2020 13:17:42 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 3/4] Kbuild: make DWARF version a choice To: Nick Desaulniers Cc: Jakub Jelinek , Linux Kbuild mailing list , Linux Kernel Mailing List , linux-toolchains@vger.kernel.org, clang-built-linux , Fangrui Song , Nathan Chancellor , Sedat Dilek , Dmitry Golovin , Alistair Delva Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 1, 2020 at 5:45 AM 'Nick Desaulniers' via Clang Built Linux wrote: > > On Mon, Nov 30, 2020 at 10:05 AM Masahiro Yamada wrote: > > > > On Wed, Nov 4, 2020 at 9:53 AM 'Nick Desaulniers' via Clang Built > > Linux wrote: > > > > > > Modifies CONFIG_DEBUG_INFO_DWARF4 to be a member of a choice. Adds an > > > explicit CONFIG_DEBUG_INFO_DWARF2, which is the default. Does so in a > > > way that's forward compatible with existing configs, and makes adding > > > future versions more straightforward. > > > > > > Suggested-by: Fangrui Song > > > Suggested-by: Masahiro Yamada > > > Signed-off-by: Nick Desaulniers > > > --- > > > Makefile | 14 ++++++++------ > > > lib/Kconfig.debug | 19 +++++++++++++++---- > > > 2 files changed, 23 insertions(+), 10 deletions(-) > > > > > > diff --git a/Makefile b/Makefile > > > index 75b1a3dcbf30..e23786a4c1c7 100644 > > > --- a/Makefile > > > +++ b/Makefile > > > @@ -826,12 +826,14 @@ else > > > DEBUG_CFLAGS += -g > > > endif > > > > > > -ifndef LLVM_IAS > > > -KBUILD_AFLAGS += -Wa,-gdwarf-2 > > > -endif > > > - > > > -ifdef CONFIG_DEBUG_INFO_DWARF4 > > > -DEBUG_CFLAGS += -gdwarf-4 > > > +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2 > > > +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4 > > > +DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y) > > > +ifneq ($(dwarf-version-y)$(LLVM_IAS),21) > > > +# Binutils 2.35+ required for -gdwarf-4+ support. > > > +dwarf-aflag := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y)) > > > +DEBUG_CFLAGS += $(dwarf-aflag) > > > > This changes the behavior. > > > > For the Dwarf-2 case, > > > > Previously, -gdwarf-2 was passed to $(CC), > > so the debug info was generated by gcc. > > > > Now, -Wa,-gdwarf-2 is passed to $(CC). > > -gdwarf-2 is handled by GNU as. > > So, the source info points to /tmp/.s > > instead of the original .c file. > > > > > > > > Handling the Dwarf capability is very complicated. > > > > Are you still working for v3? > > Yes, I plan to revisit the series based on all of the feedback thus > far. Lately I'm focused on enabling LLVM_IAS=1 for Android; but I > would like to see this land so that the Linux kernel may provide > coverage and feedback to the toolchain developers for DWARF v5 (as > well as reduced binary image sizes). Maybe later this week I'll have > time to revisit. > -- > Thanks, > ~Nick Desaulniers > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/CAKwvOdmPeOEA4dfODCKLE4A_M-SF5RBVFEf-NuiTkUTXAbh-5w%40mail.gmail.com. In my understanding, the complexity comes from the fact we are mixing up the $(CC) capability and $(AS) capability. They are orthogonal if I understand correctly. When building *.c files, the .debug* sections are generated by gcc (or clang), and embedded into the intermediate *.s files. The assembler (GAS or clang's IAS) simply transforms it into byte stream in *.o. So we do not care about the assembler capability. When building *.S files, the .debug* sections are generated by the assembler. Here, the assembler capability is important. Unless we use binutils 2.35+ or clang IAS, DWARF v2 is the only possible choice. So, we need two separate choices to handle this properly, I think. The following is the rough sketch. # The value is 2, 3, 4, or 5 depending on the assembler in use. # Unfortunately, we cannot check this by $(cc-option, -Wa,-gdwarf-4) # because GAS <= 2.34 accepts any -gdwarf-. # readelf --debug-dump=info and grep or something? config AS_SUPPORTS_DWARF_VERSION int $(shell scripts/as_dwarf_support.sh) choice "DWARF version for C code debugging" config CC_DEBUG_INFO_DWARF2 bool "..." config CC_DEBUG_INFO_DWARF4 bool "..." config CC_DEBUG_INFO_DWARF5 bool "..." depends on GCC_VERSION >= 700000 || CC_IS_CLANG depends on AS_SUPPORTS_DWARF_VERSION >= 5 help gcc7+ or clang supports this. Unfortunately, we also need to check assembler capability because GAS <= 2.34 do not understand ".file 0" endchoice choice "DWARF version for assembly code debugging" config AS_DEBUG_INFO_DWARF2 bool "..." config AS_DEBUG_INFO_DWARF4 bool "..." depends on AS_SUPPORTS_DWARF_VERSION >= 4 config AS_DEBUG_INFO_DWARF5 bool "..." depends on AS_SUPPORTS_DWARF_VERSION >= 5 endchoice -- Best Regards Masahiro Yamada