Re: FAILED: load BTF from vmlinux: Invalid argument

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

Hi Nick,

On Thu, 3 Aug 2023 13:50:02 -0700
Nick Desaulniers <ndesaulniers@google.com> wrote:

> On Thu, Aug 3, 2023 at 1:39 PM Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> >
> > Em Thu, Aug 03, 2023 at 11:02:46AM -0700, Nick Desaulniers escreveu:
> > > Hi Martin (and BTF/BPF team),
> > > I've observed 2 user reports with the error from the subject of this email.
> > > https://github.com/ClangBuiltLinux/linux/issues/1825
> > > https://bbs.archlinux.org/viewtopic.php?id=284177
> > >
> > > Any chance you could take a look at these reports and help us figure
> > > out what's going wrong here?  Nathan and I haven't been able to
> > > reproduce, but this seems to be affecting OpenMandriva (and Tomasz).
> > >
> > > Sounds like perhaps llvm-objcopy vs gnu objcopy might be a relevant detail?
> >
> > Masami had a problem with new versions of compilers that was solved
> > with:
> >
> > ------------------------ 8< --------------------------------------------
> > > To check that please tweak:
> > >
> > > ⬢[acme@toolbox perf-tools-next]$ grep DWARF ../build/v6.2-rc5+/.config
> > > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
> > > # CONFIG_DEBUG_INFO_DWARF4 is not set
> > > # CONFIG_DEBUG_INFO_DWARF5 is not set
> > > ⬢[acme@toolbox perf-tools-next]$
> > >
> > > i.e. disable CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT and enable
> > > CONFIG_DEBUG_INFO_DWARF4.
> >
> > Hm, with CONFIG_DEBUG_INFO_DWARF4, no warning were shown.
> 
> Downgrading from the now-6-year-old DWARFv5 to now-13-year-old DWARFv4
> is not what I'd consider a fix. Someday we can move to
> DWARFv5...someday...

Actually, even with DWARFv5, if I use newer clang, pahole succeded to make
BTF info. So it may depend on compiler version too.

> 
> What you describe sounds like build success, but reduction in debug info.
> 
> The reports I'm referring to seem to result in a build failure.

Yeah, it seems a different issue. I could build it at least.

Thank you,

> 
> >
> >   LD      .tmp_vmlinux.btf
> >   BTF     .btf.vmlinux.bin.o
> >   LD      .tmp_vmlinux.kallsyms1
> >
> > And
> >
> > / # strings /sys/kernel/btf/vmlinux | wc -l
> > 89921
> > / # strings /sys/kernel/btf/vmlinux | grep -w kfree
> > kfree
> >
> > It seems the BTF is correctly generated. (with DWARF5, the number of symbols
> > are about 30000.)
> 
> 
> 
> -- 
> Thanks,
> ~Nick Desaulniers


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>