Date:   Tue, 20 Oct 2020 09:20:15 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Érico Rolim <erico.erc@...il.com>,
        dwarves@...r.kernel.org, linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Hao Luo <haoluo@...gle.com>, Andrii Nakryiko <andriin@...com>
Subject: Re: Segfault in pahole 1.18 when building kernel 5.9.1 for arm64

Em Tue, Oct 20, 2020 at 11:01:39AM +0200, Jiri Slaby escreveu:
> Hi,
> 
> On 19. 10. 20, 1:18, Érico Rolim wrote:
> > I'm trying to build kernel 5.9.1 for arm64, and my dotconfig has
> > `CONFIG_DEBUG_INFO_BTF=y`, which requires pahole for building. However, pahole
> > version 1.18 segfaults during the build, as can be seen below:
> > 
> > PAHOLE: Error: Found symbol of zero size when encoding btf (sym:
> > '__kvm_nvhe_arm64_ssbd_callback_required', cu:
> > 'arch/arm64/kernel/cpu_errata.c').
> 
> The symbol is an alias coming from arch/arm64/kernel/vmlinux.lds:
> __kvm_nvhe_arm64_ssbd_callback_required = arm64_ssbd_callback_required;;
> 
> > PAHOLE: Error: Use '-j' or '--force' to ignore such symbols and force
> > emit the btf.
> > scripts/link-vmlinux.sh: line 141: 43837 Segmentation fault
> > LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
> >    LD      .tmp_vmlinux.kallsyms1
> >    KSYM    .tmp_vmlinux.kallsyms1.o
> >    LD      .tmp_vmlinux.kallsyms2
> >    KSYM    .tmp_vmlinux.kallsyms2.o
> >    LD      vmlinux
> >    BTFIDS  vmlinux
> > FAILED: load BTF from vmlinux: Unknown error -2make: ***
> > [Makefile:1162: vmlinux] Error 255
> > 
> > It is possible to force the build to continue if
> > 
> >    LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
> > 
> > in scripts/link-vmlinux.sh is changed to
> > 
> >    LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J --btf_encode_force ${1}
> > 
> > The suggested `-j` or `--force` flags don't exist, since they were removed in
> > [1]. I believe `--btf_encode_force` should be suggested instead.
> 
> Agreed, '--btf_encode_force' makes pahole to proceed without crashes.
> 
> > It should be noted that the same build, but with pahole version 1.17, works
> > without issue, so I think this is either a regression in pahole or the script
> > will need to be changed for newer versions of pahole.
> 
> Yeah, I observe the very same. I reported it at:
> https://bugzilla.suse.com/show_bug.cgi?id=1177921

Would it be possible to try with
https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?h=tmp.libbtf_encoder
?

This switches to using libbpf for the BTF encoder and may have fixed
this problem.

- Arnaldo
 
> The backtrace:
> > (gdb) where
> > #0  __memmove_sse2_unaligned_erms () at
> ../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:300
> > #1  0x00007ffff7f78346 in memcpy (__len=<optimized out>, __src=<optimized
> out>, __dest=<optimized out>, __dest=<optimized out>, __src=<optimized out>,
> __len=<optimized out>) at /usr/include/bits/string_fortified.h:34
> > #2  gobuffer__add (gb=0x555555569aa0, s=0x7fffffffb50c, len=12) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/gobuffer.c:87
> > #3  0x00007ffff7f8671f in btf_elf__add_datasec_type
> (btfe=btfe@...ry=0x555555569a40,
> section_name=section_name@...ry=0x7ffff7fa43ad ".data..percpu",
> var_secinfo_buf=var_secinfo_buf@...ry=0x555555569ac0) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/libbtf.c:721
> > #4  0x00007ffff7f8d766 in btf_elf__encode (flags=0 '\000',
> btfe=0x555555569a40) at /usr/src/debug/dwarves-1.18-1.1.x86_64/libbtf.c:857
> > #5  btf_elf__encode (btfe=0x555555569a40, flags=<optimized out>) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/libbtf.h:71
> > #6  0x00007ffff7f7fc70 in btf_encoder__encode () at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/btf_encoder.c:213
> > #7  0x00007ffff7f80d17 in cu__encode_btf (cu=0x55555638d9b0, verbose=0,
> force=false, skip_encoding_vars=false) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/btf_encoder.c:255
> > #8  0x000055555555ac4d in pahole_stealer (cu=0x55555638d9b0,
> conf_load=<optimized out>) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/pahole.c:2366
> > #9  0x00007ffff7f89dab in finalize_cu (cus=0x5555555622d0,
> dcu=0x7fffffffd080, conf=0x5555555610e0 <conf_load>, cu=0x55555638d9b0) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/dwarf_loader.c:2473
> > #10 finalize_cu_immediately (conf=0x5555555610e0 <conf_load>,
> dcu=0x7fffffffd080, cu=0x55555638d9b0, cus=0x5555555622d0) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/dwarf_loader.c:2317
> > #11 cus__load_module (cus=cus@...ry=0x5555555622d0, conf=0x5555555610e0
> <conf_load>, mod=mod@...ry=0x555555564760, dw=0x555555565960,
> elf=elf@...ry=0x555555562360, filename=0x7fffffffe846 "ss") at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/dwarf_loader.c:2473
> > #12 0x00007ffff7f8a0f1 in cus__process_dwflmod (dwflmod=0x555555564760,
> userdata=<optimized out>, name=<optimized out>, base=<optimized out>,
> arg=0x7fffffffe1b0) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/dwarf_loader.c:2518
> > #13 0x00007ffff7d4f571 in dwfl_getmodules () from /usr/lib64/libdw.so.1
> > #14 0x00007ffff7f823ed in cus__process_file (filename=0x7fffffffe846 "ss",
> fd=3, conf=<optimized out>, cus=0x5555555622d0) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/dwarf_loader.c:2571
> > #15 dwarf__load_file (cus=0x5555555622d0, conf=<optimized out>,
> filename=0x7fffffffe846 "ss") at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/dwarf_loader.c:2588
> > #16 0x00007ffff7f76771 in cus__load_file (cus=cus@...ry=0x5555555622d0,
> conf=conf@...ry=0x5555555610e0 <conf_load>, filename=0x7fffffffe846 "ss") at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/dwarves.c:1958
> > #17 0x00007ffff7f798a8 in cus__load_files (cus=0x5555555622d0,
> conf=0x5555555610e0 <conf_load>, filenames=0x7fffffffe518) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/dwarves.c:2316
> > #18 0x00005555555576fc in main (argc=3, argv=0x7fffffffe508) at
> /usr/src/debug/dwarves-1.18-1.1.x86_64/pahole.c:2687
> 
> 
> I suspect:
> commit f3d9054ba8ff1df0fc44e507e3a01c0964cabd42
> Author:     Hao Luo <haoluo@...gle.com>
> AuthorDate: Wed Jul 8 13:44:10 2020 -0700
> 
>     btf_encoder: Teach pahole to store percpu variables in vmlinux BTF.
> 
> 
> Which added this machinery (btf_elf__add_datasec_type in particular).
> 
> > - [1] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/pahole.c?h=v1.18&id=1abc001417b579b86a9b27ff88c9095d8f498a46
> > 
> > Thanks,
> > Érico
> > 
> 
> 
> -- 
> js
> suse labs

-- 

- Arnaldo

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