Re: FAILED unresolved symbol vfs_truncate on arm64 with LLVM

On Mon, Feb 8, 2021 at 7:44 PM Nathan Chancellor [off-list ref] 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.

Cheers,
Nathan