Re: [PATCH 1/1] pahole: Don't fail when encoding BTF on an object with no DWARF info

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Wed, Jul 23, 2025 at 08:00:31PM +0100, Alan Maguire wrote:
> On 22/07/2025 15:22, Arnaldo Carvalho de Melo wrote:
> > If pahole is asked to encode BTF for a file with no DWARF info, don't
> > fail, just skip it.

> > This is the case, for instance, in this file in a kernel build with
> > DWARF info generation enabled:

> >   $ pahole ../build/v6.15.0-rc4+/arch/x86/purgatory/purgatory.o
> >   libbpf: failed to find '.BTF' ELF section in ../build/v6.15.0-rc4+/arch/x86/purgatory/purgatory.o
> >   pahole: file '../build/v6.15.0-rc4+/arch/x86/purgatory/purgatory.o' has no supported type information.
> >   $

> > Before it was failing when encoding BTF for it, now:

> >   $ pahole --btf_encode ../build/v6.15.0-rc4+/arch/x86/purgatory/purgatory.o
> >   $ echo $?
> >   0
> >   $

> > Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
 
> Only potential issue I can see is that in the usual case of encoding BTF
> from DWARF in the kernel we'd probably like to fall over if we can't
> encode BTF due to DWARF absence. However current Kconfig dependencies of
> CONFIG_DEBUG_INFO_BTF mean this can't happen in practice I think so

Right, this is an exception, just some .o files out of thousands end up
without DWARF.

So I think that if we take --btf_encode as "Encode BTF from DWARF, if
DWARF is available" is a good interpretation of intent.

- Arnaldo
 
> Reviewed-by: Alan Maguire <alan.maguire@oracle.com>

Thanks!

- Arnaldo
 
> > ---
> >  pahole.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/pahole.c b/pahole.c
> > index 333e71ab65924d2c..a001ec86ef1b0908 100644
> > --- a/pahole.c
> > +++ b/pahole.c
> > @@ -3659,6 +3659,13 @@ try_sole_arg_as_class_names:
> >  			remaining = argc;
> >  			goto try_sole_arg_as_class_names;
> >  		}
> > +
> > +		if (btf_encode || ctf_encode) {
> > +			// If encoding is asked for and there is no DEBUG info to encode from,
> > +			// there are no errors, continue...
> > +			goto out_ok;
> > +		}
> > +
> >  		if (argv[remaining] != NULL) {
> >  			cus__fprintf_load_files_err(cus, "pahole", argv + remaining, err, stderr);
> >  		} else {