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

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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?

> >> 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

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




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