From: Alan Maguire <alan.maguire@oracle.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: dwarves@vger.kernel.org, Jiri Olsa <jolsa@kernel.org>,
Clark Williams <williams@redhat.com>,
Kate Carcia <kcarcia@redhat.com>,
bpf@vger.kernel.org, Arnaldo Carvalho de Melo <acme@redhat.com>,
Daniel Xu <dxu@dxuuu.xyz>, Eduard Zingerman <eddyz87@gmail.com>
Subject: Re: [PATCH 2/2] pahole: Allow asking for extra features using the '+' prefix in --btf_features
Date: Mon, 29 Apr 2024 12:16:18 +0100 [thread overview]
Message-ID: <d9e3a7ab-9799-42b0-9c6f-1809a0527867@oracle.com> (raw)
In-Reply-To: <ZiwS0_O_CTesvjLC@x1>
On 26/04/2024 21:47, Arnaldo Carvalho de Melo wrote:
> 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@kernel.org> wrote:
>>>
>>> From: Arnaldo Carvalho de Melo <acme@redhat.com>
>>>
>>> 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?
>
Yep, it would just be ignored, so wouldn't have the desired behaviour
of enabling defaults + reproducible build option.
> 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?
>
I might be missing something here, but I think we should always call out
explicitly the set of features we want in the kernel Makefile.btf
(something like [1]). The reason for this is that the concept of what is
"default" may evolve over time; for example it's going to include
Daniel's kfunc definitions for soon. That's a good thing, but it could
conceivably cause problems down the line. Consider a newer pahole - with
a newer set of defaults - running on an older kernel. In that case, we
could end up encoding BTF features we don't want. By contrast, if we
always call out the full set of BTF features we want via
--btf_features=feature1,feature2 etc we'll always get the expected set.
Plus for folks consulting the code, it's much clearer which BTF features
are in use when they look at the Makefiles for a particular kernel.
So my sense of the value of "default" is as a shortcut for testing the
latest and greatest set of BTF feature encoding, but not for use in the
kernel tree Makefiles. Thanks!
Alan
[1]
https://lore.kernel.org/bpf/20240424154806.3417662-7-alan.maguire@oracle.com/
> - 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@oracle.com>
>>> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
>>> Cc: Daniel Xu <dxu@dxuuu.xyz>
>>> Cc: Eduard Zingerman <eddyz87@gmail.com>
>>> Cc: Jiri Olsa <jolsa@kernel.org>
>>> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
>>> ---
>>> man-pages/pahole.1 | 6 ++++++
>>> pahole.c | 6 ++++++
>>> tests/reproducible_build.sh | 2 +-
>>> 3 files changed, 13 insertions(+), 1 deletion(-)
>>>
>>
>> [...]
next prev parent reply other threads:[~2024-04-29 11:16 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-19 20:57 [PATCHES 0/2] Introduce --btf_features=+extra_features syntax Arnaldo Carvalho de Melo
2024-04-19 20:57 ` [PATCH 1/2] pahole: Factor out routine to process "--btf_features=all" Arnaldo Carvalho de Melo
2024-04-19 20:57 ` [PATCH 2/2] pahole: Allow asking for extra features using the '+' prefix in --btf_features Arnaldo Carvalho de Melo
2024-04-26 20:26 ` Andrii Nakryiko
2024-04-26 20:47 ` Arnaldo Carvalho de Melo
2024-04-29 11:16 ` Alan Maguire [this message]
2024-04-29 16:46 ` Andrii Nakryiko
2024-04-29 18:48 ` Arnaldo Carvalho de Melo
2024-04-23 2:29 ` [PATCHES 0/2] Introduce --btf_features=+extra_features syntax Daniel Xu
2024-04-23 9:02 ` Alan Maguire
2024-04-23 14:22 ` Arnaldo Carvalho de Melo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=d9e3a7ab-9799-42b0-9c6f-1809a0527867@oracle.com \
--to=alan.maguire@oracle.com \
--cc=acme@kernel.org \
--cc=acme@redhat.com \
--cc=andrii.nakryiko@gmail.com \
--cc=bpf@vger.kernel.org \
--cc=dwarves@vger.kernel.org \
--cc=dxu@dxuuu.xyz \
--cc=eddyz87@gmail.com \
--cc=jolsa@kernel.org \
--cc=kcarcia@redhat.com \
--cc=williams@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.