On Mon, Feb 08, 2021 at 10:56:36PM -0800, Andrii Nakryiko wrote: > On Mon, Feb 8, 2021 at 10:13 PM Andrii Nakryiko > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > On Mon, Feb 8, 2021 at 10:09 PM Andrii Nakryiko > > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > > > 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") > > > > > > ... > > > > > > > ... 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) > > > > Ok, the problem appears to be not in DWARF, but in mcount_loc data. > vfs_truncate's address is not recorded as ftrace-attachable, and thus > pahole ignores it. I don't know why this happens and it's quite > strange, given vfs_truncate is just a normal global function. > > I'd like to understand this issue before we try to fix it, but there > is at least one improvement we can make: pahole should check ftrace > addresses only for static functions, not the global ones (global ones > should be always attachable, unless they are special, e.g., notrace > and stuff). We can easily check that by looking at the corresponding > symbol. But I'd like to verify that vfs_truncate is ftrace-attachable > for that particular kernel. For that we'll need Nathan's cooperation, > unless someone else can build an arm64 kernel with the same problem > and check. Sure, just let me know what I need to do and I can do it! Cheers, Nathan > > > > > $ 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 > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/CAEf4Bzax90hn_5axpnCpW%2BE6gVc1mtUgCXWqmxV0tJ4Ud7bsaA%40mail.gmail.com.
