Re: Problem with BTF generation on mips64el

[Tony Ambardar <tony.ambardar@gmail.com>]

Hi Jiri,

On Fri, May 31, 2024 at 10:13:21AM +0200, Jiri Olsa wrote:
> On Fri, May 31, 2024 at 10:17:53AM +0800, Hengqi Chen wrote:
> > Hi Tony,
> > 
> > On Fri, May 31, 2024 at 9:30 AM Tony Ambardar <tony.ambardar@gmail.com> wrote:
> > >
> > > Hello,
> > >
> > > For some time now I'm seeing multiple issues during BTF generation while
> > > building recent kernels targeting mips64el, and would appreciate some help
> > > to understand and fix the problems.
> > >
> > > Some relate to resolve_btfids:
> > >
> > > >   LD      vmlinux
> > > >   BTFIDS  vmlinux
> > > > WARN: resolve_btfids: unresolved symbol bpf_verify_pkcs7_signature
> > > > WARN: resolve_btfids: unresolved symbol bpf_session_cookie
> > > > WARN: resolve_btfids: unresolved symbol bpf_lookup_user_key
> > > > WARN: resolve_btfids: unresolved symbol bpf_lookup_system_key
> > > > WARN: resolve_btfids: unresolved symbol bpf_key_put
> > > > WARN: resolve_btfids: unresolved symbol bpf_iter_task_next
> > > > WARN: resolve_btfids: unresolved symbol bpf_iter_css_task_new
> > > > WARN: resolve_btfids: unresolved symbol bpf_get_file_xattr
> > > > WARN: resolve_btfids: unresolved symbol bpf_ct_insert_entry
> > > > WARN: resolve_btfids: unresolved symbol bpf_cgroup_release
> > > > WARN: resolve_btfids: unresolved symbol bpf_cgroup_from_id
> > > > WARN: resolve_btfids: unresolved symbol bpf_cgroup_acquire
> > > > WARN: resolve_btfids: unresolved symbol bpf_arena_free_pages
> > > >   NM      System.map
> > > >   SORTTAB vmlinux
> > > >   OBJCOPY vmlinux.32
> > >
> > > These do not appear to be #ifdef-related and have similar past reports [1].
> 
> I can reproduce the warning just for bpf_session_cookie,
> which has fix in progress:
>   https://lore.kernel.org/bpf/20240531071557.MvfIqkn7@linutronix.de/T/#t

I gather there are different root causes for these warnings. From the link,
the issue with bpf_session_cookie seems related to conditional compilation,
which have come up before on the mailing list IIRC.

In comparison, consider my above warning for bpf_key_put, which is defined
in kernel/trace/bpf_trace.c. This kfunc is guarded by CONFIG_KEY, which is
enabled in my config and so not the issue. I can in fact see the global
text symbol for bpf_key_put in bpf_trace.o, but not in vmlinux.

So I suspect the warnings might come from linker or optimization problems,
or perhaps even an issue related to the __bpf_kfunc annotation. WDYT?

> 
> > >
> > > I also see many pahole failures during BTF encoding of modules, such as:
> > >
> > > >   CC [M]  net/ipv6/netfilter/nft_fib_ipv6.mod.o
> > > >   CC [M]  net/ipv6/netfilter/ip6t_REJECT.mod.o
> > > >   CC [M]  net/psample/psample.mod.o
> > > >   LD [M]  crypto/cmac.ko
> > > >   BTF [M] crypto/cmac.ko
> > > > die__process: DW_TAG_compile_unit, DW_TAG_type_unit, DW_TAG_partial_unit
> > > > or DW_TAG_skeleton_unit expected got member (0xd)!
> > 
> > The issue seems to be related to elfutils. Have you tried build from
> > the latest elfutils source ?
> > I saw the latest MIPS backend in elfutils already implemented the
> > reloc_simple_type hook.
> 
> hi,
> +1, could you also check the pahole version you used?

No luck I'm afraid with using the latest elfutils as suggested.

I used pahole v1.26 in my original testing for this bug report, as noted
below (might have been buried a bit).

> 
> jirka
> 
> SNIP
>
> > > Details of the git commit and build environment are as follows:
> > >
> > > > $ git log -1 --oneline  bpf/master
> > > > 9dfdb706e164 (bpf/master) selftests/bpf: fix inet_csk_accept prototype in
> > > > test_sk_storage_tracing.c
> > > >
> > > > $ lsb_release -a
> > > > Description:    Ubuntu 22.04.4 LTS
> > > >
> > > > $ cat gcc-compile.txt
> > > > ARCH=mips CROSS_COMPILE=mips64el-linux-gnuabi64- CC="ccache ${CROSS_COMPILE}gcc" make -j6
> > > >
> > > > $ mips64el-linux-gnuabi64-gcc --version
> > > > mips64el-linux-gnuabi64-gcc (Ubuntu 10.3.0-1ubuntu1) 10.3.0
> > > >
> > > > $ mips64el-linux-gnuabi64-ld --version
> > > > GNU ld (GNU Binutils for Ubuntu) 2.38
> > > >
> > > > $ pahole --version
> > > > v1.26
> 
> SNIP
>
> > > I'd be grateful if some of the BTF/pahole experts could please review this
> > > issue and share next steps or other details I might provide.
> > >
> > > Thanks,
> > > Tony Ambardar
> > >
> > > Link: https://lore.kernel.org/all/202401211357.OCX9yllM-lkp@intel.com/ [1]
> > > Link: https://github.com/acmel/dwarves/issues/45 [2]
> > 
> > Cheers,
> > Hengqi

Thanks,
Tony