linux-kernel - Re: [RFC PATCH v1 08/16] unwind_user: Enable archs that save RA/FP in other registers

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Message-ID: <20250717081014.784251f8@gandalf.local.home>
Date: Thu, 17 Jul 2025 08:10:14 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Jens Remus <jremus@...ux.ibm.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org,
 Steven Rostedt <rostedt@...nel.org>, Heiko Carstens <hca@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Ilya Leoshkevich <iii@...ux.ibm.com>,
 Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Namhyung Kim
 <namhyung@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Andrii
 Nakryiko <andrii@...nel.org>, Indu Bhagat <indu.bhagat@...cle.com>, "Jose
 E. Marchesi" <jemarch@....org>, Beau Belgrave <beaub@...ux.microsoft.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton
 <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>, Florian Weimer
 <fweimer@...hat.com>, Sam James <sam@...too.org>
Subject: Re: [RFC PATCH v1 08/16] unwind_user: Enable archs that save RA/FP
 in other registers

On Thu, 17 Jul 2025 13:28:25 +0200
Jens Remus <jremus@...ux.ibm.com> wrote:

> >> +	default:
> >> +		WARN_ON_ONCE(1);
> >> +		goto done;  
> > 
> > The default case will never happen, can we make it a BUG()?  
> 
> Whatever Steve and you agree on.  I am new to Kernel development.

Keep the WARN_ON(). Linus has yelled at people for using BUG() when a
WARN_ON() would do.

WARN_ON() is meant for things that should never happen. BUG() is reserved
for places in the kernel that is dangerous to continue.

It's even documented:

  https://docs.kernel.org/process/deprecated.html#bug-and-bug-on

-- Steve