On Mon, Feb 8, 2021 at 9:23 PM Nathan Chancellor <nathan@xxxxxxxxxx> 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@xxxxxxxxxx> 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") ... $ 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
