linux-kernel - Re: [PATCH v13 02/14] unwind_user: Add frame pointer support

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Message-ID: <20250710130859.41f3d5d0@batman.local.home>
Date: Thu, 10 Jul 2025 13:08:59 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Jens Remus <jremus@...ux.ibm.com>
Cc: Steven Rostedt <rostedt@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org,
 Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
 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>, Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik
 <gor@...ux.ibm.com>
Subject: Re: [PATCH v13 02/14] unwind_user: Add frame pointer support

On Thu, 10 Jul 2025 17:41:36 +0200
Jens Remus <jremus@...ux.ibm.com> wrote:

> cfa + frame->ra_off could be aligned by chance.  So could
> cfa + frame->fp_off be as well of course.
> 
> On s390 the CFA must be aligned (as the SP must be aligned) and the
> FP and RA offsets from CFA must be aligned, as pointer / 64-bit integers
> (such as 64-bit register values) must be aligned as well.
> 
> So the CFA (and/or offset), FP offset, and RA offset could be validated
> individually.  Not sure if that would be over engineering though.

I wonder if we should just validate that cfa is aligned? Would that work?

I would think that ra_off and fp_off should be aligned as well and if
cfa is aligned then it would still be aligned when adding those offsets.

-- Steve