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Date: Wed, 19 Aug 2020 20:23:10 -0700 From: Yonghong Song <yhs@...com> To: Fāng-ruì Sòng <maskray@...gle.com>, Jiri Olsa <jolsa@...nel.org> CC: Nick Desaulniers <ndesaulniers@...gle.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Mark Wielaard <mjw@...hat.com>, Nick Clifton <nickc@...hat.com>, Jesper Dangaard Brouer <brouer@...hat.com>, Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>, Andrii Nakryiko <andriin@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...omium.org>, clang-built-linux <clang-built-linux@...glegroups.com> Subject: Re: [PATCH bpf-next] tools/resolve_btfids: Fix sections with wrong alignment On 8/19/20 7:27 PM, Fāng-ruì Sòng wrote: >>>> section(36) .comment, size 44, link 0, flags 30, type=1 >>>> section(37) .debug_aranges, size 45684, link 0, flags 800, type=1 >>>> - fixing wrong alignment sh_addralign 16, expected 8 >>>> section(38) .debug_info, size 129104957, link 0, flags 800, type=1 >>>> - fixing wrong alignment sh_addralign 1, expected 8 >>>> section(39) .debug_abbrev, size 1152583, link 0, flags 800, type=1 >>>> - fixing wrong alignment sh_addralign 1, expected 8 >>>> section(40) .debug_line, size 7374522, link 0, flags 800, type=1 >>>> - fixing wrong alignment sh_addralign 1, expected 8 >>>> section(41) .debug_frame, size 702463, link 0, flags 800, type=1 >>>> section(42) .debug_str, size 1017571, link 0, flags 830, type=1 >>>> - fixing wrong alignment sh_addralign 1, expected 8 >>>> section(43) .debug_loc, size 3019453, link 0, flags 800, type=1 >>>> - fixing wrong alignment sh_addralign 1, expected 8 >>>> section(44) .debug_ranges, size 1744583, link 0, flags 800, type=1 >>>> - fixing wrong alignment sh_addralign 16, expected 8 >>>> section(45) .symtab, size 2955888, link 46, flags 0, type=2 >>>> section(46) .strtab, size 2613072, link 0, flags 0, type=3 > > I think this is resolve_btfids's bug. GNU ld and LLD are innocent. > These .debug_* sections work fine if their sh_addralign is 1. > When the section flag SHF_COMPRESSED is set, the meaningful alignment > is Elf64_Chdr::ch_addralign, after the header is uncompressed. > > On Wed, Aug 19, 2020 at 2:30 PM Yonghong Song <yhs@...com> wrote: >> >> >> >> On 8/19/20 11:16 AM, Nick Desaulniers wrote: >>> On Wed, Aug 19, 2020 at 10:36 AM Jiri Olsa <jolsa@...hat.com> wrote: >>>> >>>> On Wed, Aug 19, 2020 at 08:31:51AM -0700, Yonghong Song wrote: >>>>> >>>>> >>>>> On 8/19/20 2:23 AM, Jiri Olsa wrote: >>>>>> The data of compressed section should be aligned to 4 >>>>>> (for 32bit) or 8 (for 64 bit) bytes. >>>>>> >>>>>> The binutils ld sets sh_addralign to 1, which makes libelf >>>>>> fail with misaligned section error during the update as >>>>>> reported by Jesper: >>>>>> >>>>>> FAILED elf_update(WRITE): invalid section alignment Jiri, Since Fangrui mentioned this is not a ld/lld bug, then changing alighment from 1 to 4 might have some adverse effect for the binary, I guess. Do you think we could skip these .debug_* sections somehow in elf parsing in resolve_btfids? resolve_btfids does not need to read these sections. This way, no need to change their alignment either. Yonghong >>>>>> >>>>>> While waiting for ld fix, we can fix compressed sections >>>>>> sh_addralign value manually. >>> >>> Is there a bug filed against GNU ld? Link? >>> >>>>>> >>>>>> Adding warning in -vv mode when the fix is triggered: >>>>>> >>>>>> $ ./tools/bpf/resolve_btfids/resolve_btfids -vv vmlinux >>>>>> ... >>>>>> section(36) .comment, size 44, link 0, flags 30, type=1 >>>>>> section(37) .debug_aranges, size 45684, link 0, flags 800, type=1 >>>>>> - fixing wrong alignment sh_addralign 16, expected 8 >>>>>> section(38) .debug_info, size 129104957, link 0, flags 800, type=1 >>>>>> - fixing wrong alignment sh_addralign 1, expected 8 >>>>>> section(39) .debug_abbrev, size 1152583, link 0, flags 800, type=1 >>>>>> - fixing wrong alignment sh_addralign 1, expected 8 >>>>>> section(40) .debug_line, size 7374522, link 0, flags 800, type=1 >>>>>> - fixing wrong alignment sh_addralign 1, expected 8 >>>>>> section(41) .debug_frame, size 702463, link 0, flags 800, type=1 >>>>>> section(42) .debug_str, size 1017571, link 0, flags 830, type=1 >>>>>> - fixing wrong alignment sh_addralign 1, expected 8 >>>>>> section(43) .debug_loc, size 3019453, link 0, flags 800, type=1 >>>>>> - fixing wrong alignment sh_addralign 1, expected 8 >>>>>> section(44) .debug_ranges, size 1744583, link 0, flags 800, type=1 >>>>>> - fixing wrong alignment sh_addralign 16, expected 8 >>>>>> section(45) .symtab, size 2955888, link 46, flags 0, type=2 >>>>>> section(46) .strtab, size 2613072, link 0, flags 0, type=3 >>>>>> ... >>>>>> update ok for vmlinux >>>>>> >>>>>> Another workaround is to disable compressed debug info data >>>>>> CONFIG_DEBUG_INFO_COMPRESSED kernel option. >>>>> >>>>> So CONFIG_DEBUG_INFO_COMPRESSED is required to reproduce the bug, right? >>>> >>>> correct >>>> >>>>> >>>>> I turned on CONFIG_DEBUG_INFO_COMPRESSED in my config and got a bunch of >>>>> build failures. >>>>> >>>>> ld: drivers/crypto/virtio/virtio_crypto_algs.o: unable to initialize >>>>> decompress status for section .debug_info >>>>> ld: drivers/crypto/virtio/virtio_crypto_algs.o: unable to initialize >>>>> decompress status for section .debug_info >>>>> ld: drivers/crypto/virtio/virtio_crypto_algs.o: unable to initialize >>>>> decompress status for section .debug_info >>>>> ld: drivers/crypto/virtio/virtio_crypto_algs.o: unable to initialize >>>>> decompress status for section .debug_info >>>>> drivers/crypto/virtio/virtio_crypto_algs.o: file not recognized: File format >>>>> not recognized >>>>> >>>>> ld: net/llc/llc_core.o: unable to initialize decompress status for section >>>>> .debug_info >>>>> ld: net/llc/llc_core.o: unable to initialize decompress status for section >>>>> .debug_info >>>>> ld: net/llc/llc_core.o: unable to initialize decompress status for section >>>>> .debug_info >>>>> ld: net/llc/llc_core.o: unable to initialize decompress status for section >>>>> .debug_info >>>>> net/llc/llc_core.o: file not recognized: File format not recognized >>>>> >>>>> ... >>>>> >>>>> The 'ld' in my system: >>>>> >>>>> $ ld -V >>>>> GNU ld version 2.30-74.el8 >>>>> Supported emulations: >>>>> elf_x86_64 >>>>> elf32_x86_64 >>>>> elf_i386 >>>>> elf_iamcu >>>>> i386linux >>>>> elf_l1om >>>>> elf_k1om >>>>> i386pep >>>>> i386pe >>> >>> According to Documentation/process/changes.rst, the minimum supported >>> version of GNU binutils for the kernels is 2.23. Can you upgrade to >>> that and confirm that you still observe the issue? I don't want to >>> spend time chasing bugs in old, unsupported versions of GNU binutils, >>> especially as Jiri notes, 2.26 is required for >>> CONFIG_DEBUG_INFO_COMPRESSED. We can always strengthen the Kconfig >>> check for it. Otherwise, I'm not familiar with the observed error >>> message. >> >> I built a "ld" with latest binutils-gdb repo and I can reproduced >> the issue. Indeed applying the patch here fixed the issue. So >> I think there is no need to investigate since upstream exhibits >> the exact issue described here. >> >>> >>>>> $ >>>>> >>>>> Do you know what is the issue here? >>>> >>>> mine's: GNU ld version 2.32-31.fc31 >>>> >>>> there's version info in commit: >>>> 10e68b02c861 Makefile: support compressed debug info >>>> >>>> Compress the debug information using zlib. Requires GCC 5.0+ or Clang >>>> 5.0+, binutils 2.26+, and zlib. >>>> >>>> cc-ing Nick Desaulniers, author of that patch.. any idea about the error above? >>>> >>>> thanks, >>>> jirka >>>> >>> >>> > > >
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