On Tue, Jan 12, 2021 at 1:57 AM Yonghong Song <yhs@xxxxxx> wrote: > > > > On 1/11/21 1:30 PM, Sedat Dilek wrote: > > On Mon, Jan 11, 2021 at 10:03 PM Andrii Nakryiko > > <andrii.nakryiko@xxxxxxxxx> wrote: > >> > >> On Mon, Jan 11, 2021 at 9:56 AM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote: > >>> > >>> On Mon, Jan 11, 2021 at 5:05 PM Yonghong Song <yhs@xxxxxx> wrote: > >>>> > >>>> > >>>> > >>>> On 1/11/21 4:48 AM, Sedat Dilek wrote: > >>>>> Hi BPF maintainers and Mashiro, > >>>>> > >>>>> Debian started to use CONFIG_DEBUG_INFO_BTF=y. > >>>>> > >>>>> My kernel-build fails like this: > >>>>> > >>>>> + info BTFIDS vmlinux > >>>>> + [ != silent_ ] > >>>>> + printf %-7s %s\n BTFIDS vmlinux > >>>>> BTFIDS vmlinux > >>>>> + ./tools/bpf/resolve_btfids/resolve_btfids vmlinux > >>>>> FAILED: load BTF from vmlinux: Invalid argument > >>>>> > >>>>> The root cause is my selfmade LLVM toolchain has no BPF support. > >>>> > >>>> linux build should depend on LLVM toolchain unless you use LLVM to build > >>>> kernel. > >>>> > >>>>> > >>>>> $ which llc > >>>>> /home/dileks/src/llvm-toolchain/install/bin/llc > >>>>> > >>>>> $ llc --version > >>>>> LLVM (http://llvm.org/ ): > >>>>> LLVM version 11.0.1 > >>>>> Optimized build. > >>>>> Default target: x86_64-unknown-linux-gnu > >>>>> Host CPU: sandybridge > >>>>> > >>>>> Registered Targets: > >>>>> x86 - 32-bit X86: Pentium-Pro and above > >>>>> x86-64 - 64-bit X86: EM64T and AMD64 > >>>>> > >>>>> Debian's llc-11 shows me BPF support is built-in. > >>>>> > >>>>> I see the breakag approx. 3 hours after the start of my kernel-build - > >>>>> in the stage "vmlinux". > >>>>> After 2 faulures in my build (2x 3 hours of build-time) I have still > >>>>> no finished Linux v5.11-rc3 kernel. > >>>>> This is a bit frustrating. > >>>> > >>>> You mean "BTFIDS vmlinux" takes more than 3 hours here? > >>>> Maybe a bug in resolve_btfids due to somehow different ELF format > >>>> resolve_btfids need to handle? > >>>> > >>> > >>> [ CC Tom ] > >>> > >>> OMG no. > >>> > >>> 3 hours up to running scripts/link-vmlinux.sh. > >>> > >>> In the meantime I have built a LLVM toolchain with BPF support. > >>> > >>> $ llc --version > >>> LLVM (http://llvm.org/ ): > >>> LLVM version 11.0.1 > >>> Optimized build. > >>> Default target: x86_64-unknown-linux-gnu > >>> Host CPU: sandybridge > >>> > >>> Registered Targets: > >>> bpf - BPF (host endian) > >>> bpfeb - BPF (big endian) > >>> bpfel - BPF (little endian) > >> > >> As Yonghong mentioned, you don't need BPF target support in Clang to > >> build the kernel, so the issue is elsewhere. It's somewhere between > >> generated DWARF (we've seen multiple bugs in DWARF over time), > >> pahole's BTF output and resolve_btfids's handling of that BTF. I've > >> CC'ed Jiri, who can help with resolve_btfids. > >> > >> Meanwhile, if you can provide SHA from which you built Clang, kernel > >> config you used, and probably exact invocation of the build you used, > >> it would help reproduce the issue. > >> > > > > OK, I see I have here DWARF v5 support patchset applied and enabled. > > > > Furthermore: I applied latest clang-cfi. > > > > This is with LLVM v11.0.1 final aka 43ff75f2c3feef64f9d73328230d34dac8832a91. > > Did you use llvm to compile kernel? If this is the case, latest pahole > will segfault. I am using latest trunk llvm. It is possible that > generated dwarf with llvm is different from generated dwarf with gcc > and pahole did not process it correctly. I did not get time to > debug this though. > Yes, I used LLVM/Clang to compile the kernel. - Sedat - > > > > My kernel-config is attached. > > > > [1] https://patchwork.kernel.org/project/linux-kbuild/patch/20201204011129.2493105-1-ndesaulniers@xxxxxxxxxx/ > > [2] https://patchwork.kernel.org/project/linux-kbuild/patch/20201204011129.2493105-2-ndesaulniers@xxxxxxxxxx/ > > [3] https://github.com/samitolvanen/linux/commits/clang-cfi > > > >>> x86 - 32-bit X86: Pentium-43ff75f2c3feef64f9d73328230d34dac8832a91 > > Pro and above > >>> x86-64 - 64-bit X86: EM64T and AMD64 > >>> > >>> Tom reported BTF issues with pahole v1.19 (see [2] and [3]): > >>> "I ran into this same bug trying to build the Fedora kBROKEN_5-11-rc3-CONFIG_DEBUG_INFO_BTF-y-FAILED-load-BTF-from-vmlinux.txt > > ernel. The > >>> problem is that pahole segfaults at: scripts/link-vmlinux.sh:131. This > >>> looks to me like a bug in pahole." > >>> > >>> pahole ToT (post v1.19) offers some BTF fixes - I have manually build > >>> and use it. > >>> > >>> Building a new Linux-kernel... > >>> > >>> - Sedat - > >>> > >>> [1] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/ > >>> [2] https://github.com/ClangBuiltLinux/tc-build/issues/129#issuecomment-758026878 > >>> [3] https://github.com/ClangBuiltLinux/tc-build/issues/129#issuecomment-758056553 > >> > >> There are no significant bug fixes between pahole 1.19 and master that > >> would solve this problem, so let's try to repro this. > >> > > > > You are right pahole fom latest Git does not solve the issue. > > > > + info BTFIDS vmlinux > > + [ != silent_ ] > > + printf %-7s %s\n BTFIDS vmlinux > > BTFIDS vmlinux > > + ./tools/bpf/resolve_btfids/resolve_btfids vmlinux > > FAILED: load BTF from vmlinux: Invalid argument > > > > - Sedat - > > > >>> > >>> > >>> > >>>>> > >>>>> What about doing pre-checks - means before doing a single line of > >>>>> compilation - to check for: > >>>>> 1. Required binaries > >>>>> 2. Required support of whatever feature in compiler, linker, toolchain etc. > >>>>> > >>>>> Recently, I fell over depmod binary not found in my PATH - in one of > >>>>> the last steps (modfinal) of the kernel build. > >>>>> > >>>>> Any ideas to improve the situation? > >>>>> ( ...and please no RTFM, see links below. ) > >>>>> > >>>>> Thanks. > >>>>> > >>>>> Regards, > >>>>> - Sedat - > >>>>> > >>>>> > >>>>> [0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/link-vmlinux.sh#n144 > >>>>> [1] https://salsa.debian.org/kernel-team/linux/-/commit/929891281c61ce4403ddd869664c949692644a2f > >>>>> [2] https://www.kernel.org/doc/html/latest/bpf/bpf_devel_QA.html?highlight=pahole#llvm > >>>>> [3] https://www.kernel.org/doc/html/latest/bpf/btf.html?highlight=pahole#btf-generation > >>>>>
