From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f47.google.com (mail-wm1-f47.google.com [209.85.128.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 325D67E for ; Wed, 7 Sep 2022 04:27:21 +0000 (UTC) Received: by mail-wm1-f47.google.com with SMTP id d5so8018067wms.5 for ; Tue, 06 Sep 2022 21:27:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date; bh=+FvGAIQA6g0/NKJ5BUw0y3xxvyJZjvMl5VPNjIGS+gw=; b=fpFTiwJW/9HvCH0gN6PmxI2K53uPz9gBdr1uC6fWNNa+Yx2q4zXBfLBnLrLL4w3XVx SLH0tKobr810W8SeuIsF/R2PCYkbKSLv+lmLCZskEcCW/ReZBReXUqszaDzEfFcTKv5a nlDcskBpwttZ34MdXcWaUtu6tDmajbA9c41A/neaA2mh3GnOvQKKqzuB1ioTDStJQQXt xna02FYQMvtubUmq9TwhowBPyJ7e1nA1MBzfX5LWcMRawYKCTR5xizIKZeEBxzDEnR/2 uIhvFAPVIakt8m/dzFlXO7ui+42zBaUsdjRuE1ZQ5tGPkhpeNVPMTm3qieQMennUpYpz Ss5Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date; bh=+FvGAIQA6g0/NKJ5BUw0y3xxvyJZjvMl5VPNjIGS+gw=; b=INAgpbMOLu8iJ3IUoNUhoouqLtiJnSvlYFvwyTUbHxs/pYzhrQUh6SF6xJhAVO6nLN VjVnhy0lHJfeiCsSvkk3OAAKhSuCTahM+WCXAJ8v/LVE9dPCNcCWz3q7Bfb+UdzhJwSh gQu5So65pDu41pR0orOErsL/GGilKxNwnxXT0ZBFnVMIbc+PysDEnk2b4z1MMLNyiygn nz/ZNCZYFQuszuAGObMTtglCscn64fLCpalccJNYjO7JtVDipU8AkQ6Wg12bOs3Q0/RW n4YxPu5m3x9GAhi006EubKdXNo7KEirD+I9BPa6pPC5E2GNpdbe8SBvyGefcA/Z+Rcvg XWRA== X-Gm-Message-State: ACgBeo2wBeHTw28696/MkzWgm+zK0KC2whrW5PUxPFWwgdXkjDEssx5z 6+TXqEOlM1zlO4pyJrTAXXCgB5esPKRoFdohpYU56A== X-Google-Smtp-Source: AA6agR7UdGjjmLFmbENHxkNrUGWnPqjf+1gmEg2hCrJPIR4g+trGtUUyjsmLEtD6nr9EhMHcg0XC6n+JH7pk509CMSI= X-Received: by 2002:a05:600c:ad2:b0:3a5:36ca:ec38 with SMTP id c18-20020a05600c0ad200b003a536caec38mr685223wmr.21.1662524839234; Tue, 06 Sep 2022 21:27:19 -0700 (PDT) Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20220831184408.2778264-1-ndesaulniers@google.com> <20220831184408.2778264-5-ndesaulniers@google.com> In-Reply-To: From: Nick Desaulniers Date: Tue, 6 Sep 2022 21:27:07 -0700 Message-ID: Subject: Re: [PATCH v2 4/5] Makefile.debug: re-enable debug info for .S files To: Masahiro Yamada Cc: Michal Marek , Nathan Chancellor , Tom Rix , Linux Kbuild mailing list , Linux Kernel Mailing List , clang-built-linux , X86 ML , Dmitrii Bundin , Fangrui Song , Alexey Alexandrov , Bill Wendling , Greg Thelen Content-Type: text/plain; charset="UTF-8" On Mon, Sep 5, 2022 at 12:50 AM Masahiro Yamada wrote: > > On Thu, Sep 1, 2022 at 3:44 AM Nick Desaulniers wrote: > > > > Alexey reported that the fraction of unknown filename instances in > > kallsyms grew from ~0.3% to ~10% recently; Bill and Greg tracked it down > > to assembler defined symbols, which regressed as a result of: > > > > commit b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1") > > > > In that commit, I allude to restoring debug info for assembler defined > > symbols in a follow up patch, but it seems I forgot to do so in > > > > commit a66049e2cf0e ("Kbuild: make DWARF version a choice") > > > > This patch does a few things: > > 1. Add -g to KBUILD_AFLAGS. This will instruct the compiler to instruct > > the assembler to emit debug info. But this can cause an issue for > > folks using a newer compiler but older assembler, because the > > implicit default DWARF version changed from v4 to v5 in gcc-11 and > > clang-14. > > > > What kind of bad things happen for "KBUILD_AFLAGS += -g"? > > > I think 'gcc -g -c -o foo.o foo.S' will invoke 'as --gdwarf-2' as the backend > if gcc is configured to work with old binutils. That's fine for CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT I think? What other problems were you envisioning? > > > > > > diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug > > index 9f39b0130551..46e88f0ca998 100644 > > --- a/scripts/Makefile.debug > > +++ b/scripts/Makefile.debug > > @@ -4,18 +4,32 @@ ifdef CONFIG_DEBUG_INFO_SPLIT > > DEBUG_CFLAGS += -gsplit-dwarf > > else > > DEBUG_CFLAGS += -g > > +KBUILD_AFLAGS += -g > > endif > > > > -ifndef CONFIG_AS_IS_LLVM > > -KBUILD_AFLAGS += -Wa,-gdwarf-2 > > +ifdef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > > +# gcc-11+, clang-14+ > > +ifeq ($(call cc-min-version, 110000, 140000),y) > > +dwarf-version-y := 5 > > +else > > +dwarf-version-y := 4 > > > > If you explicitly specify the DWARF version > for CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT, > what is the point of CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT? > > > When CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y, > I believe the right thing to do is to pass only -g, > and let the tool do whatever it thinks is appropriate. Ok, sure, I will revise. > > > > > > > > endif > > - > > -ifndef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > > +else # !CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > > dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4 > > dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5 > > DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y) > > endif > > > > +# Binutils 2.35+ (or clang) required for -gdwarf-{4|5}. > > +# https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=31bf18645d98b4d3d7357353be840e320649a67d > > +ifneq ($(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y)),) > > > > When is this as-option supposed to fail? > > > Binutils <= 2.34 always accepts whatever -gdwarf-* option. > Surprisingly or not, it accepts -gdwarf-6, -gdwarf-7, ... > > No matter what DWARF version you specify, GAS silently downgrades > it to DWARF-2. > > > masahiro@zoe:~/tools/binutils-2.34/bin$ ./as --version | head -n 1 > GNU assembler (GNU Binutils) 2.34 > masahiro@zoe:~/tools/binutils-2.34/bin$ cat /dev/null | ./as -gdwarf-5 > -o /dev/null - > masahiro@zoe:~/tools/binutils-2.34/bin$ echo $? > 0 > masahiro@zoe:~/tools/binutils-2.34/bin$ cat /dev/null | ./as > -gdwarf-100 -o /dev/null - > masahiro@zoe:~/tools/binutils-2.34/bin$ echo $? > 0 ah, right. Maybe an explicit version check is necessary then. > > > > > Overall, I am not convinced with this patch. > > > > Please see the attached patch. > Is there any problem with writing this more simply? Thanks for the inspiration, I will use that as an inspiration/base for a new patch. -- Thanks, ~Nick Desaulniers