Re: Fwd: [RESEND] BTF is not generated for gcc-built kernel with the latest pahole

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On Tue, 1 Aug 2023 15:28:38 -0300
Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx> wrote:

> Sorry, replied only to Alan :-\
> 
> - Arnaldo
> 
> ---------- Forwarded message ---------
> From: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx>
> Date: Tue, Aug 1, 2023 at 3:26 PM
> Subject: Re: [RESEND] BTF is not generated for gcc-built kernel with
> the latest pahole
> To: Alan Maguire <alan.maguire@xxxxxxxxxx>
> 
> 
> On Tue, Aug 1, 2023 at 2:37 PM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
> > On 01/08/2023 02:01, Masami Hiramatsu (Google) wrote:
> > > On Mon, 31 Jul 2023 16:45:24 +0100
> > > Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
> 
> > >> Unfortunately (or fortunately?) I haven't been able to reproduce so far
> > >> I'm afraid. I used your config and built gcc 13 from source; everything
> > >> worked as expected, with no warnings or missing functions (aside from
> > >> the ones skipped due to inconsistent prototypes etc).
> > >
> > > Yeah, so I think gcc-11.3 is suspicious too (and it seems fixed in gcc-13).
> 
> See below, but this one is interesting, gcc-13 works with
> CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y?

I'm using gcc-11.3, and it seems to work.

> 
> > >> One other thing I can think of - is it possible libdw[arf]/libelf
> > >> versions might be having an effect here? I'm using libdwarf.so.1.2,
> > >> libdw-0.188, libelf-0.188. I can try and match yours. Thanks!
> > >
> > > Both libdw/libelf are 0.181. I didn't install libdwarf.
> > > Hmm, I should update the libdw (elfutils) too.
> >
> > That might help. Thanks!
> 
> Probably he needs to tweak these CONFIG_ entries:
> 
> ⬢[acme@toolbox perf-tools]$ 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]$
> 
> And make it use CONFIG_DEBUG_INFO_DWARF4=y,
> CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=n

OK, interesting. Let me check again with DWARF4.

Thank you!

> 
> For DWARF5 I need to forward port what I have in:
> 
> https://git.kernel.org/pub/scm/devel/pahole/pahole.git/log/?h=WIP-imported-unit
> 
> - Arnaldo


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>




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