linux-kernel - Re: [PATCH 1/1] tools build: Fix rust feature detection

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Message-ID: <aYubAAZ10CfYsmZx@x1>
Date: Tue, 10 Feb 2026 17:54:24 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Dmitry Dolgov <9erthalion6@...il.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>,
	Ian Rogers <irogers@...gle.com>,
	James Clark <james.clark@...aro.org>, Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 1/1] tools build: Fix rust feature detection

On Tue, Feb 10, 2026 at 09:16:18PM +0100, Dmitry Dolgov wrote:
> > On Tue, Feb 10, 2026 at 09:26:22AM -0300, Arnaldo Carvalho de Melo wrote:
> > I tried here building it with rust installed, it detected, ok, then I
> > removed and tried to rebuild, it still thinks rust is there:

> > [...]

> > I.e. it doesn't rebuild perf and thus doesn't notice that it doesn't
> > have what is needed, if I touch some other file and thus it triggers a
> > rebuild, it still manages to build it...

> Yeah, looks like the problem is due to rust not adding any actual depedencies
> into the dep-info file, when compiling the feature test file:

> 	/perf/feature/test-rust.d: test-rust.rs

> 	/perf/feature/test-rust.bin: test-rust.rs

> 	test-rust.rs:

> To fix that I've tried to add an extra dependency on the rust binary on top of
> that after the compilation is finished. While hacky, it worked just fine, and
> perf catched it when rust was removed. Haven't faced any issues after few
> rounds of installing/removing rust either. If this approach sound fine, I can
> post the patch tomorrow.

Looks hacky, can't we just try to run:

⬢ [acme@...lbx linux]$ HAVE_RUST=$(rustc --version > /dev/null ; echo $?)
⬢ [acme@...lbx linux]$ echo $HAVE_RUST
0
⬢ [acme@...lbx linux]$ HAVE_RUST=$(arustc --version > /dev/null ; echo $?)
bash: arustc: command not found
⬢ [acme@...lbx linux]$ echo $HAVE_RUST
127
⬢ [acme@...lbx linux]$

How would your dep on the rust binary work? where would you expect it to
be? It may be installed on some different path, etc.

Perhaps there is precedent with some other component...

- Arnaldo