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=-19.2 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=ham 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 2B13EC10F29 for ; Tue, 17 Mar 2020 05:21:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E4E3F20719 for ; Tue, 17 Mar 2020 05:21:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="VTzELuAK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725871AbgCQFV0 (ORCPT ); Tue, 17 Mar 2020 01:21:26 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:46393 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725794AbgCQFV0 (ORCPT ); Tue, 17 Mar 2020 01:21:26 -0400 Received: by mail-pf1-f196.google.com with SMTP id c19so11269126pfo.13 for ; Mon, 16 Mar 2020 22:21:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=Gct5Div9yO3xZ7uj+wMJ5J+JaU8FAOUzHSAPaDD/q3A=; b=VTzELuAKDRdhLYXZTeD6naICUU0PwcEisv0CUwH07hsgCDgTbAtpVqWKV0qVfjTAmM h77cznbW1Ye3Xvjab1cgE2z4+orY/pBhUOUrSywBm1geg+cdB6va27ONoD479vOr3rbk Jyhd7103Ppbo+lTH8L7Z9g4tE0X5cPew7Al4mBrwTJYmdL9YaWxCuI5t5GPXpxbvTRDO qZ0h2VpfbEpP9zd3RtKygyTzMBu/iGs6XKrFDxdxoj4Pkdzws4nl6Fu42fSDRFcfaTA3 0nnnYy3vf+/75aESv5/5c11KKEx3bMfmgxYHP7oGnpqoJjtmYNstkPl8HoyXMEYv8R7N KQDQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=Gct5Div9yO3xZ7uj+wMJ5J+JaU8FAOUzHSAPaDD/q3A=; b=TwxYC01WvPv+k2bVdv+TG9W14OgraLq0O3ekg4qchJ/2znKFfkquKrzixMnGWyEbwm QRjtAhDAYc2+PKQcYNi1abPqPG3mJNDuQOBfs0xF6xL7iVQN80lF7uSXBR/UFMxHWBXD SdXnv23GNUP79n4twIQPkiEdg2cdomj6A6mm1UNatHKoHeyauGiLayfbL6mX0DzlgV9w vVnxBfErnqPxu5fBQswNVB/KFWRyS2ERIBpVc/8XBPQ2T1z3nrzvIHSlmqPBJjOJkg2+ rXrkV9V3v3kF/s673apZCVTml0uxUPlmDJuak9mYj54pm/EQDYIwkaW1zmSp7t573Ycw MLQg== X-Gm-Message-State: ANhLgQ173t/0u8XK5m8ObGOcPP+tBv2/0t4lEInYhUUxWJnaiEk2FhF0 o0JvDBKTnDP/tDGCp0LBFskFyg== X-Google-Smtp-Source: ADFU+vvXsZLUhxvYBpj8hFqsViWBU1qsKu1fkjaecEPliHmI0WaB0rpdd/Ajv2EFPQzHNAsDPS8Ycg== X-Received: by 2002:a63:d143:: with SMTP id c3mr3197691pgj.171.1584422484251; Mon, 16 Mar 2020 22:21:24 -0700 (PDT) Received: from google.com ([2620:15c:2ce:0:9efe:9f1:9267:2b27]) by smtp.gmail.com with ESMTPSA id e9sm1374336pjt.23.2020.03.16.22.21.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Mar 2020 22:21:23 -0700 (PDT) Date: Mon, 16 Mar 2020 22:21:20 -0700 From: Fangrui Song To: Andrii Nakryiko Cc: bpf , Networking , Daniel Borkmann , Nick Desaulniers , Nathan Chancellor , clang-built-linux@googlegroups.com, Stanislav Fomichev , "David S. Miller" , Alexei Starovoitov Subject: Re: [PATCH bpf v2] bpf: Support llvm-objcopy and llvm-objdump for vmlinux BTF Message-ID: <20200317052120.diawg3a75kxl5hkn@google.com> References: <20200317011654.zkx5r7so53skowlc@google.com> <20200317033701.w7jwos7mvfnde2t2@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 2020-03-16, Andrii Nakryiko wrote: >On Mon, Mar 16, 2020 at 8:37 PM Fangrui Song wrote: >> >> On 2020-03-16, Andrii Nakryiko wrote: >> >On Mon, Mar 16, 2020 at 6:17 PM Fangrui Song wrote: >> >> >> >> Simplify gen_btf logic to make it work with llvm-objcopy and >> >> llvm-objdump. We just need to retain one section .BTF. To do so, we can >> >> use a simple objcopy --only-section=.BTF instead of jumping all the >> >> hoops via an architecture-less binary file. >> >> >> >> We use a dd comment to change the e_type field in the ELF header from >> >> ET_EXEC to ET_REL so that .btf.vmlinux.bin.o will be accepted by lld. >> >> >> >> Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux") >> >> Cc: Stanislav Fomichev >> >> Cc: Nick Desaulniers >> >> Tested-by: Nick Desaulniers >> >> Reported-by: Nathan Chancellor >> >> Link: https://github.com/ClangBuiltLinux/linux/issues/871 >> >> Signed-off-by: Fangrui Song >> >> --- >> >> scripts/link-vmlinux.sh | 13 ++----------- >> >> 1 file changed, 2 insertions(+), 11 deletions(-) >> >> >> >> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh >> >> index dd484e92752e..84be8d7c361d 100755 >> >> --- a/scripts/link-vmlinux.sh >> >> +++ b/scripts/link-vmlinux.sh >> >> @@ -120,18 +120,9 @@ gen_btf() >> >> >> >> info "BTF" ${2} >> >> vmlinux_link ${1} >> >> - LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} >> > >> >Is it really tested? Seems like you just dropped .BTF generation step >> >completely... >> >> Sorry, dropped the whole line:/ >> I don't know how to test .BTF . I can only check readelf -S... >> >> Attached the new patch. >> >> >> From 02afb9417d4f0f8d2175c94fc3797a94a95cc248 Mon Sep 17 00:00:00 2001 >> From: Fangrui Song >> Date: Mon, 16 Mar 2020 18:02:31 -0700 >> Subject: [PATCH bpf v2] bpf: Support llvm-objcopy and llvm-objdump for >> vmlinux BTF >> >> Simplify gen_btf logic to make it work with llvm-objcopy and llvm-objdump. >> We use a dd comment to change the e_type field in the ELF header from >> ET_EXEC to ET_REL so that .btf.vmlinux.bin.o can be accepted by lld. >> >> Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux") >> Cc: Stanislav Fomichev >> Cc: Nick Desaulniers >> Reported-by: Nathan Chancellor >> Link: https://github.com/ClangBuiltLinux/linux/issues/871 >> Signed-off-by: Fangrui Song >> --- >> scripts/link-vmlinux.sh | 14 +++----------- >> 1 file changed, 3 insertions(+), 11 deletions(-) >> >> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh >> index dd484e92752e..b23313944c89 100755 >> --- a/scripts/link-vmlinux.sh >> +++ b/scripts/link-vmlinux.sh >> @@ -120,18 +120,10 @@ gen_btf() >> >> info "BTF" ${2} >> vmlinux_link ${1} >> - LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} >> + ${PAHOLE} -J ${1} > >I'm not sure why you are touching this line at all. LLVM_OBJCOPY part >is necessary, pahole assumes llvm-objcopy by default, but that can >(and should for objcopy) be overridden with LLVM_OBJCOPY. Why is LLVM_OBJCOPY assumed? What if llvm-objcopy is not available? This is confusing that one tool assumes llvm-objcopy while the block below immediately uses GNU objcopy (without this patch). e83b9f55448afce3fe1abcd1d10db9584f8042a6 "kbuild: add ability to generate BTF type info for vmlinux" does not say why LLVM_OBJCOPY is set. >> >> - # dump .BTF section into raw binary file to link with final vmlinux >> - bin_arch=$(LANG=C ${OBJDUMP} -f ${1} | grep architecture | \ >> - cut -d, -f1 | cut -d' ' -f2) >> - bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \ >> - awk '{print $4}') >> - ${OBJCOPY} --change-section-address .BTF=0 \ >> - --set-section-flags .BTF=alloc -O binary \ >> - --only-section=.BTF ${1} .btf.vmlinux.bin >> - ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \ >> - --rename-section .data=.BTF .btf.vmlinux.bin ${2} >> + # Extract .BTF section, change e_type to ET_REL, to link with final vmlinux >> + ${OBJCOPY} --only-section=.BTF ${1} ${2} && printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 >> } >> >> # Create ${2} .o file with all symbols from the ${1} object file >> -- >> 2.25.1.481.gfbce0eb801-goog >>