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=-11.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 3466DC10F29 for ; Tue, 17 Mar 2020 05:31:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F2A8720663 for ; Tue, 17 Mar 2020 05:31:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="WLVD/zf0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726452AbgCQFbU (ORCPT ); Tue, 17 Mar 2020 01:31:20 -0400 Received: from mail-qk1-f194.google.com ([209.85.222.194]:34608 "EHLO mail-qk1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726345AbgCQFbU (ORCPT ); Tue, 17 Mar 2020 01:31:20 -0400 Received: by mail-qk1-f194.google.com with SMTP id f3so30539520qkh.1; Mon, 16 Mar 2020 22:31:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=XXy14v1H5qtRvYyPugSKBtcwiv16J7o5FfkzIcp1Jlg=; b=WLVD/zf0i+fUP2SyAHSItt3BWS8cKI0clBoC9LIiM3ehdMWnswF/nkA5cETYMZsbqy +L0tTFNm6AtmM3SBMGSwcAtCeomly91l2L9HnoOMJPOM0fxjMDCpIoEuD0WKAYfAPf0B 4m6vbaWEhM5M+4GpYdXh8X6InPv7YqueG7no23nz11SE/fMAO/NF7LFgxQS0rHiZk7xk Z5dGuXxY0BKK/4NBFUeGLcYE9mBKynGhNXYr1StqIgFZug4+9n+phE1On3Me98B1Q3ZB hcyZCkBpUatDDXMBGeucLqqKPcwQfu7b2dpuSnrAXSv8R0qITqJQQYppnxPF6moPiRY1 j6tQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=XXy14v1H5qtRvYyPugSKBtcwiv16J7o5FfkzIcp1Jlg=; b=Pelj0ryNQPJSIBrvowhpbPr8cfbsf7of4JIcdW3EdGa5LsLYkdQExIMEas4mjO8uSB pNw7eTIE42sAxaS7yO4i2D3b6PBvR67lvHqMD9JgrI/YCkX7zcbITKOjrB/c7+M7As9e DnWxpK06rBHg2gQGoUjbdhjEJZ44OAund7P0Aipjar/Q5Qs8RydfX5boHUO2cjWZLkzL VhhxguLheuAf3v9dc9eHbXwG8uczgoZWYVEwQRVEKl2lFkTfx7xth2ihLSFy03DKlxUd A2xhWsuzgPaqnP/meME5lm18rvY09Vodj2GiYK7r1dEzgSNYCbpymQ2XxRiKHGUj/9rl 790g== X-Gm-Message-State: ANhLgQ2tXK2LoTKyXmZHiIDdm99gcfi7T28Qd1WdSOmoC69C/7+CP0z7 jCJtIcz03QxhXB3t+eZ1raKdEK0al7LvUlC+xHqagU8E X-Google-Smtp-Source: ADFU+vty44T5xwlfAzeuiobyB7fjJWb1Rpr+0yfo3i+2ZJqxMA/vMgeoUouXiWE0Oeuq0BtwT/fUQH/bJKd0MegjsO0= X-Received: by 2002:a37:e40d:: with SMTP id y13mr3240261qkf.39.1584423078366; Mon, 16 Mar 2020 22:31:18 -0700 (PDT) MIME-Version: 1.0 References: <20200317011654.zkx5r7so53skowlc@google.com> <20200317033701.w7jwos7mvfnde2t2@google.com> <20200317052120.diawg3a75kxl5hkn@google.com> In-Reply-To: <20200317052120.diawg3a75kxl5hkn@google.com> From: Andrii Nakryiko Date: Mon, 16 Mar 2020 22:31:07 -0700 Message-ID: Subject: Re: [PATCH bpf v2] bpf: Support llvm-objcopy and llvm-objdump for vmlinux BTF To: Fangrui Song Cc: bpf , Networking , Daniel Borkmann , Nick Desaulniers , Nathan Chancellor , clang-built-linux@googlegroups.com, Stanislav Fomichev , "David S. Miller" , Alexei Starovoitov Content-Type: text/plain; charset="UTF-8" Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, Mar 16, 2020 at 10:21 PM Fangrui Song wrote: > > > 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 ${1} > > > >I'm not sure why you are touching this line at all. LLVM_OBJCOPY part > >is necessary, pahole assumes llvm-objcopy by default, but that can > >(and should for objcopy) be overridden with LLVM_OBJCOPY. > > Why is LLVM_OBJCOPY assumed? What if llvm-objcopy is not available? It's pahole assumption that we have to live with. pahole assumes llvm-objcopy internally, unless it is overriden with LLVM_OBJCOPY env var. So please revert this line otherwise you are breaking it for GCC objcopy case. > This is confusing that one tool assumes llvm-objcopy while the block > below immediately uses GNU objcopy (without this patch). > > e83b9f55448afce3fe1abcd1d10db9584f8042a6 "kbuild: add ability to > generate BTF type info for vmlinux" does not say why LLVM_OBJCOPY is > set. > > >> > >> - # dump .BTF section into raw binary file to link with final vmlinux > >> - bin_arch=$(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 > >>