linux-kernel - Re: [PATCH] sched: Make clangd usable

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Message-ID: <20250526090435.GD31726@noisy.programming.kicks-ass.net>
Date: Mon, 26 May 2025 11:04:35 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com, rafael@...nel.org,
	viresh.kumar@...aro.org, mathieu.desnoyers@...icios.com,
	paulmck@...nel.org, hannes@...xchg.org, surenb@...gle.com
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, tj@...nel.org,
	masahiroy@...nel.org
Subject: Re: [PATCH] sched: Make clangd usable

On Mon, May 26, 2025 at 10:59:43AM +0200, Peter Zijlstra wrote:
> On Fri, May 23, 2025 at 06:43:48PM +0200, Peter Zijlstra wrote:
> 
> > Setting up clangd on the kernel source is a giant pain in the arse
> > (this really should be improved), but once you do manage, you run into
> > dumb stuff like the above.
> 
> Given Steve asked for an emacs lsp plugin, I'm guessing he's going to be
> wanting this part too.
> 
> The way I got clangd working is something like:
> 
> 
> $ mkdir clangd-build
> $ make O=clangd-build allmodconfig
> $ make O=clangd-build LLVM=-19 -j128
> $ cd clangd-build
> $ ../scripts/clang-tools/gen_compile_commands.py
> $ sed -i "s'randomize-layout-seed-file=\.'randomize-layout-seed-file=$PWD'g" compile_commands.json
> $ cd -
> $ ln -s clang-build/compile_commands.json 
> 
> I then also have:
> 
> $ cat .clangd
> # https://clangd.llvm.org/config
> CompileFlags:
>   Add: -ferror-limit=0
> Diagnostics:
>   ClangTidy:
>     Remove: bugprone-sizeof-expression
>   UnusedIncludes: None
> Completion:
>   HeaderInsertion: Never
> $
> 
> 
> This has you sit on about 10G of build output, and while it is very
> tempting to do make clean on clangd-build, this will in fact ruin
> things. You can however manually delete all the compiler output, just
> not the various generated files.
> 
> I've not been annoyed enough to (or out of diskspace enough) to go stare
> at fixing the Makefiles to make all this easier. But ideally it would be
> possible to do a no-op build to just generate the .cmd files without
> doing any actual compiling -- building allmodconfig is slow, doubly so
> with allmodconfig.

.. with clang -- gcc is still significantly faster; and I know there's a
k.org clang build optimized for kernels, however I seem to end up using
either distro builds or custom builds, neither of which are having
whatever goodness the k.org build has.

> Or maybe this is already possible and I just didn't find the magic
> incantations.