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Message-ID: <CAEf4BzYvri7wzRnGH_qQbavXOx5TfBA0qx4nYVnn=YNGv+vNVw@mail.gmail.com>
Date: Mon, 8 Feb 2021 22:13:10 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Veronika Kabatova <vkabatov@...hat.com>,
Jiri Olsa <jolsa@...nel.org>
Subject: Re: FAILED unresolved symbol vfs_truncate on arm64 with LLVM
On Mon, Feb 8, 2021 at 10:09 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Mon, Feb 8, 2021 at 9:23 PM Nathan Chancellor <nathan@...nel.org> wrote:
> >
> > On Mon, Feb 08, 2021 at 08:45:43PM -0800, Andrii Nakryiko wrote:
> > > On Mon, Feb 8, 2021 at 7:44 PM Nathan Chancellor <nathan@...nel.org> wrote:
> > > >
> > > > Hi all,
> > > >
> > > > Recently, an issue with CONFIG_DEBUG_INFO_BTF was reported for arm64:
> > > > https://groups.google.com/g/clang-built-linux/c/de_mNh23FOc/m/E7cu5BwbBAAJ
> > > >
> > > > $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
> > > > LLVM=1 O=build/aarch64 defconfig
> > > >
> > > > $ scripts/config \
> > > > --file build/aarch64/.config \
> > > > -e BPF_SYSCALL \
> > > > -e DEBUG_INFO_BTF \
> > > > -e FTRACE \
> > > > -e FUNCTION_TRACER
> > > >
> > > > $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
> > > > LLVM=1 O=build/aarch64 olddefconfig all
> > > > ...
> > > > FAILED unresolved symbol vfs_truncate
> > > > ...
> > > >
> > > > My bisect landed on commit 6e22ab9da793 ("bpf: Add d_path helper")
> > > > although that seems obvious given that is what introduced
> > > > BTF_ID(func, vfs_truncate).
> > > >
> > > > I am using the latest pahole v1.20 and LLVM is at
> > > > https://github.com/llvm/llvm-project/commit/14da287e18846ea86e45b421dc47f78ecc5aa7cb
> > > > although I can reproduce back to LLVM 10.0.1, which is the earliest
> > > > version that the kernel supports. I am very unfamiliar with BPF so I
> > > > have no idea what is going wrong here. Is this a known issue?
> > > >
> > >
> > > I'll skip the reproduction games this time and will just request the
> > > vmlinux image. Please upload somewhere so that we can look at DWARF
> > > and see what's going on. Thanks.
> > >
> >
> > Sure thing, let me know if this works. I uploaded in two places to make
> > it easier to grab:
> >
> > zstd compressed:
> > https://github.com/nathanchance/bug-files/blob/3b2873751e29311e084ae2c71604a1963f5e1a48/btf-aarch64/vmlinux.zst
> >
>
> Thanks. I clearly see at least one instance of seemingly well-formed
> vfs_truncate DWARF declaration. Also there is a proper ELF symbol for
> it. Which means it should have been generated in BTF, but it doesn't
> appear to be, so it does seem like a pahole bug. I (or someone else
> before me) will continue tomorrow.
>
> $ llvm-dwarfdump vmlinux
> ...
>
> 0x00052e6f: DW_TAG_subprogram
> DW_AT_name ("vfs_truncate")
> DW_AT_decl_file
> ("/home/nathan/cbl/src/linux/include/linux/fs.h")
> DW_AT_decl_line (2520)
> DW_AT_prototyped (true)
> DW_AT_type (0x000452cb "long int")
> DW_AT_declaration (true)
> DW_AT_external (true)
>
> 0x00052e7b: DW_TAG_formal_parameter
> DW_AT_type (0x00045fc6 "const path*")
>
> 0x00052e80: DW_TAG_formal_parameter
> DW_AT_type (0x00045213 "long long int")
>
> ...
>
... and here's the *only* other one (not marked as declaration, but I
thought we already handle that, Jiri?):
0x01d0da35: DW_TAG_subprogram
DW_AT_low_pc (0xffff80001031f430)
DW_AT_high_pc (0xffff80001031f598)
DW_AT_frame_base (DW_OP_reg29)
DW_AT_GNU_all_call_sites (true)
DW_AT_name ("vfs_truncate")
DW_AT_decl_file ("/home/nathan/cbl/src/linux/fs/open.c")
DW_AT_decl_line (69)
DW_AT_prototyped (true)
DW_AT_type (0x01cfdfe4 "long int")
DW_AT_external (true)
> $ llvm-readelf -s vmlinux | rg vfs_truncate
> 15013: ffff800011c22418 4 OBJECT LOCAL DEFAULT 24
> __BTF_ID__func__vfs_truncate__609
> 22531: ffff80001189fe0d 0 NOTYPE LOCAL DEFAULT 17
> __kstrtab_vfs_truncate
> 22532: ffff8000118a985b 0 NOTYPE LOCAL DEFAULT 17
> __kstrtabns_vfs_truncate
> 22534: ffff800011873b7c 0 NOTYPE LOCAL DEFAULT 8
> __ksymtab_vfs_truncate
> 176099: ffff80001031f430 360 FUNC GLOBAL DEFAULT 2 vfs_truncate
>
> $ bpftool btf dump file vmlinux | rg vfs_truncate
> <nothing>
>
> > uncompressed:
> > https://1drv.ms/u/s!AsQNYeB-IEbqjQiUOspbEdXx49o7?e=ipA9Hv
> >
> > Cheers,
> > Nathan
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