linux-kernel - Re: [PATCH 1/2] tools/build: Add a feature test for libopenssl

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Message-ID: <aUD6DH_zAI6trA6M@google.com>
Date: Mon, 15 Dec 2025 22:19:56 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Quentin Monnet <qmo@...nel.org>
Cc: Ian Rogers <irogers@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>, bpf@...r.kernel.org,
	James Clark <james.clark@...aro.org>, Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org, KP Singh <kpsingh@...nel.org>
Subject: Re: [PATCH 1/2] tools/build: Add a feature test for libopenssl

Hello,

On Fri, Dec 05, 2025 at 10:28:03AM +0000, Quentin Monnet wrote:
> 2025-12-04 22:27 UTC-0800 ~ Ian Rogers <irogers@...gle.com>
> > On Thu, Dec 4, 2025 at 3:52 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >>
> >> On Thu, Dec 04, 2025 at 01:16:54PM -0300, Arnaldo Carvalho de Melo wrote:
> >>> On Wed, Dec 03, 2025 at 04:34:56PM -0800, Ian Rogers wrote:
> >>>> On Wed, Dec 3, 2025 at 3:29 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >>>>>
> >>>>> It's used by bpftool and the kernel build.  Let's add a feature test so
> >>>>> that perf can decide what to do based on the availability.
> >>>>
> >>>> It seems strange to add a feature test that bpftool is missing and
> >>>> then use it only in the perf build. The signing of bpf programs isn't
> >>>
> >>> It is strange indeed, I agree that since we don't use BPF signing at
> >>> this point in the perf BPf skels, then we could just bootstrap a bpftool
> >>> without such feature and continue building the existing features.
> >>>
> >>> Adding the bpftool maintainer to the CC list, Quentin?
> >>
> >> I've already talked to Quentin and they want libopenssl as a
> >> requirement.
> >>
> >> https://lore.kernel.org/linux-perf-users/e44f70bf-8f50-4a4b-97b8-eaf988aabced@kernel.org/
> > 
> > You can have libopenssl as a requirement and have a bootstrap bpftool
> > that doesn't require it, as the bootstrap version only provides
> > minimal features typically to just build bpftool. You can also have
> > libopenssl as a requirement and have a feature test that fails in the
> > bpftool build saying you are missing a requirement. Having the perf
> > build detect that a feature for the bpftool dependency is missing is
> > fine as we can then recommend installing bpftool or the missing
> > dependency, but doing this without bpftool also doing something just
> > seems inconsistent.
> > 
> > Thanks,
> > Ian
> 
> 
> From bpftool's perspective, it doesn't really make sense to skip the
> OpenSSL dependency for the bootstrap version, given that we want to ship
> the main binary with the signing feature: so you could build a bootstrap
> version without signing, but you won't be able to use it to build the
> final binary because, well, you miss a required dependency.
> 
> This being said, if it really makes it easier for you to build perf, I'd
> be open to adjusting the bootstrap version, as long as it doesn't affect
> the final bpftool build. It might lead to further headaches if someone
> needs to sign the BPF programs when building perf in the future though.
> 
> I'm also OK with adding a dependency check with a simple build error for
> bpftool, although we don't currently do it for other required
> dependencies in bpftool.

Ok, to make a progress, I'll add this series to perf-tools tree for
v6.19 first.

Thanks,
Namhyung