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=-13.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 B94EEC2BB1D for ; Tue, 17 Mar 2020 16:24:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B69C20738 for ; Tue, 17 Mar 2020 16:24:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=fomichev-me.20150623.gappssmtp.com header.i=@fomichev-me.20150623.gappssmtp.com header.b="EgT9v/aR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726549AbgCQQYK (ORCPT ); Tue, 17 Mar 2020 12:24:10 -0400 Received: from mail-pg1-f195.google.com ([209.85.215.195]:44648 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726207AbgCQQYK (ORCPT ); Tue, 17 Mar 2020 12:24:10 -0400 Received: by mail-pg1-f195.google.com with SMTP id 37so12001470pgm.11 for ; Tue, 17 Mar 2020 09:24:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fomichev-me.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=3gLHCw1k1vgin5ImJr7e+a6EB7LHD7UzoYRzly3/8qo=; b=EgT9v/aR37CWq7iFaT0oY9LSc6BsugpDhQ7/fV9k59U/ro8irWn7ex6HLrOw4Mt5OL 7xcIzOwrIwKHqugjTlDJrmkjx/PLsJ9pN9/hMlEGvgVnaQe9KFJkgL9BkkXRx1cKq3Pg /at+xO6E6LJGlNoKpUfusRqPDE7WTt533GNouZA9HGG7jQtO1wY1VnszWSo69BKNzvk1 1jyI8LbJ4T2JjQXEKFgFAtC9H37wmlu432UurOQSJY8HqYIy7mzWAMO8oYG5coJ32ipi ImDcFjTJNKOtcwYMTLHwuExg1Kve6LLfvzZR8M87FQOEvlfP8YXIjJQs1fyMdYbO0hBM ijqQ== 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:user-agent; bh=3gLHCw1k1vgin5ImJr7e+a6EB7LHD7UzoYRzly3/8qo=; b=PQm76R5VeDqWFXVpLIvZ4UigIZ3i+M4hXS88yWYPNpCcnDgNIA85dZpHlh1GVsbvaK cxDtqH/FL2hIP09LIcy3I5GC2jJLcq0IskvOJQonM5H2W/dbgm0X6nNyrPtd/R+IsqFd TKXECEWn+CL2XoMSGYNrR4PuhuNRykq/RZajJld16NZ5diV/n9/LdsoQW5dYln0oju0D dGdoybc6R+DeXGmUYOcjUrTDdqlRo1WAM4dVlWvngLY8W3hXHljsMWeZoqDBbzlFRFav W+xLLhC2DFfcaIfEJQvYY4+bttGX2X5PFH2+U9eN+I00USfQvhXrlIuDwWQiEl24admX Qq2w== X-Gm-Message-State: ANhLgQ0U2x5p9fN8cTtUef2StmSxuZeoDBN9Egc0v5s+ihhB3/KPPyqE a2EomTshu+/DLVVsYce5gl9f/Q== X-Google-Smtp-Source: ADFU+vu3ccDtnSUmt2sRX4YsJ3IGwbVyko3v299XzImXGkiQTr3h57D88UbgQpM5ciNsKHhnNzj5oQ== X-Received: by 2002:a63:d255:: with SMTP id t21mr46599pgi.114.1584462247864; Tue, 17 Mar 2020 09:24:07 -0700 (PDT) Received: from localhost ([2601:646:8f00:18d9:d0fa:7a4b:764f:de48]) by smtp.gmail.com with ESMTPSA id d6sm3303583pjz.39.2020.03.17.09.24.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Mar 2020 09:24:07 -0700 (PDT) Date: Tue, 17 Mar 2020 09:24:05 -0700 From: Stanislav Fomichev To: Fangrui Song Cc: Andrii Nakryiko , bpf , Networking , Daniel Borkmann , Nick Desaulniers , Nathan Chancellor , clang-built-linux@googlegroups.com, Stanislav Fomichev , "David S. Miller" , Alexei Starovoitov Subject: Re: [PATCH bpf v3] bpf: Support llvm-objcopy and llvm-objdump for vmlinux BTF Message-ID: <20200317162405.GB2459609@mini-arch.hsd1.ca.comcast.net> References: <20200317011654.zkx5r7so53skowlc@google.com> <20200317033701.w7jwos7mvfnde2t2@google.com> <20200317052120.diawg3a75kxl5hkn@google.com> <20200317054359.snyyojyf6gjxufij@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200317054359.snyyojyf6gjxufij@google.com> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 03/16, Fangrui Song wrote: > On 2020-03-16, Andrii Nakryiko wrote: > > 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 ${1} > > > > > > > >I'm not sure why you are touching this line at all. LLVM_OBJCOPY part > > > >is necessary, pahole assumes llvm-objcopy by default, but that can > > > >(and should for objcopy) be overridden with LLVM_OBJCOPY. > > > > > > Why is LLVM_OBJCOPY assumed? What if llvm-objcopy is not available? > > > > It's pahole assumption that we have to live with. pahole assumes > > llvm-objcopy internally, unless it is overriden with LLVM_OBJCOPY env > > var. So please revert this line otherwise you are breaking it for GCC > > objcopy case. > > Acknowledged. Uploaded v3. > > I added back 2>/dev/null which was removed by a previous change, to > suppress GNU objcopy warnings. The warnings could be annoying in V=1 > output. > > > > This is confusing that one tool assumes llvm-objcopy while the block > > > below immediately uses GNU objcopy (without this patch). > > > > > > e83b9f55448afce3fe1abcd1d10db9584f8042a6 "kbuild: add ability to > > > generate BTF type info for vmlinux" does not say why LLVM_OBJCOPY is > > > set. > > > > > > >> > > > >> - # dump .BTF section into raw binary file to link with final vmlinux > > > >> - bin_arch=$(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 > > > >> > > From ca3597477542453e9f63185c27c162da081a4baf Mon Sep 17 00:00:00 2001 > From: Fangrui Song > Date: Mon, 16 Mar 2020 22:38:23 -0700 > Subject: [PATCH bpf v3] bpf: Support llvm-objcopy and llvm-objdump for > vmlinux BTF > > Simplify gen_btf logic to make it work with llvm-objcopy and llvm-objdump. > Add 2>/dev/null to suppress GNU objcopy (but not llvm-objcopy) warnings > "empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?" > Our use of --only-section drops many SHF_ALLOC sections which will essentially nullify > program headers. When used as linker input, program headers are simply > ignored. > > We use a dd command 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. > Accepting ET_EXEC as an input file is an extremely rare GNU ld feature > that lld does not intend to support, because this is very error-prone. > > 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 | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) > > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh > index dd484e92752e..c3e808a89d4a 100755 > --- a/scripts/link-vmlinux.sh > +++ b/scripts/link-vmlinux.sh > @@ -122,16 +122,8 @@ gen_btf() > vmlinux_link ${1} > LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} > - # dump .BTF section into raw binary file to link with final vmlinux > - bin_arch=$(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} ${2} 2> /dev/null && printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 No, it doesn't work unfortunately, I get "in-kernel BTF is malformed" from the kernel. I think that's because -O binary adds the following: $ nm .btf.vmxlinux.bin 00000000002f7bc9 D _binary__btf_vmlinux_bin_end 00000000002f7bc9 A _binary__btf_vmlinux_bin_size 0000000000000000 D _binary__btf_vmlinux_bin_start While non-binary mode doesn't: $ nm .btf.vmxlinux.bin We don't add them manually in the linker map and expect objcopy to add them, see: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/kernel/bpf/btf.c#n3480 > } > # Create ${2} .o file with all symbols from the ${1} object file > -- > 2.25.1.481.gfbce0eb801-goog >