Re: [PATCH 2/2] pahole: Allow asking for extra features using the '+' prefix in --btf_features

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On Fri, Apr 26, 2024 at 01:26:40PM -0700, Andrii Nakryiko wrote:
> On Fri, Apr 19, 2024 at 1:58 PM Arnaldo Carvalho de Melo
> <acme@xxxxxxxxxx> wrote:
> >
> > From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> >
> > Instead of the somewhat confusing:
> >
> >   --btf_features=all,reproducible_build
> >
> > That means "'all' the standard BTF features plus the 'reproducible_build'
> > extra BTF feature", use + directly, making it more compact:
> >
> >   --btf_features=+reproducible_build
> >
> 
> for older paholes that don't yet know about + syntax, but support
> --btf_features, will this effectively disable all features or how will
> it work?
> 
> I'm thinking from the perspective of using +reproducible_build
> unconditionally in kernel's build scripts, will it regress something
> for current pahole versions?

Well, I think it will end up being discarded just like "all" or
"default", no? I.e. those were keywords not grokked by older pahole
versions, so ignored as we're not using --btf_features_strict, right?

Alan?

But then we're not yet using --btf_features in scripts/Makefile.btf,
right?

But as Daniel pointed out and Alan (I think) agreed, for things like
scripts we probably end up using the most verbose thing as:

	--btf_features=default,reproducible_build

to mean a set (the default set of BTF options) + an optional/extra
feature (reproducibe_build), that for people not used to the + syntax
may be more descriptive (I really think that both are confusing for
beginners knowing nothing about BTF and its evolution, etc).

Alan, also we released 1.26 with "all" meaning what we now call
"default", so we need to keep both meaning the same thing, right?

- Arnaldo
 
> > In the future we may want the '-' counterpart as a way to _remove_ some
> > of the standard set of BTF features.
> >
> > Cc: Alan Maguire <alan.maguire@xxxxxxxxxx>
> > Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> > Cc: Daniel Xu <dxu@xxxxxxxxx>
> > Cc: Eduard Zingerman <eddyz87@xxxxxxxxx>
> > Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> > Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > ---
> >  man-pages/pahole.1          | 6 ++++++
> >  pahole.c                    | 6 ++++++
> >  tests/reproducible_build.sh | 2 +-
> >  3 files changed, 13 insertions(+), 1 deletion(-)
> >
> 
> [...]




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