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: <20250717080555.4647863b@gandalf.local.home>
Date: Thu, 17 Jul 2025 08:05:55 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Jens Remus <jremus@...ux.ibm.com>, 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 00:24:47 -0700
Josh Poimboeuf <jpoimboe@...nel.org> wrote:

> > The only time I ever use BUG() is if it's too dangerous to continue (like a
> > function graph trampoline that gets corrupted and has no place to return
> > to). In general, usage of BUG() should be avoided.  
> 
> This is an unreachable code path, but __builtin_unreachable() is crap
> due to undefined behavior.  IMO, BUG() for unreachable paths is cleaner
> than WARN_ON_ONCE(), but it doesn't matter much either way I suppose.

Linus has stated that BUG() should be avoided too. If the code changes in
the future and this suddenly becomes a reachable path, would you rather
have a WARN or a BUG? If you don't have your system set up properly,
the BUG may not even show you why your system crashed.

-- Steve