linux-kernel - Re: [PATCH 11/12] unwind: Implement compat fp unwind

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Message-ID: <20251024134024.GT4067720@noisy.programming.kicks-ass.net>
Date: Fri, 24 Oct 2025 15:40:24 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Jens Remus <jremus@...ux.ibm.com>
Cc: jpoimboe@...nel.org, rostedt@...nel.org,
	Indu Bhagat <indu.bhagat@...cle.com>, linux-kernel@...r.kernel.org,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH 11/12] unwind: Implement compat fp unwind

On Wed, Oct 22, 2025 at 04:55:01PM +0200, Jens Remus wrote:
> Hello Peter!
> 
> On 10/20/2025 12:39 PM, Peter Zijlstra wrote:
> > On Mon, Oct 20, 2025 at 11:16:45AM +0200, Jens Remus wrote:
> >> On 10/17/2025 5:47 PM, Jens Remus wrote:
> 
> >>> In SFrame the CFA, FP, and RA offsets are unscaled.  Would it be ok, if
> >>> unwind user sframe would factor state->ws from those offset values?  What
> >>> if they were not aligned?  unwind user sframe would then have to fail.
> >>
> >> Sorry that I did not immediately think about the most obvious solution
> >> tho above issues:  to not factor out the word size from the frame CFA,
> >> FP, and RA offsets.  What do you think about making the following
> >> changes to this and giyour subsequent patch?  That would work nicely
> >> with unwind user sframe.
> > 
> > 
> > Yes, this should do nicely. I've made the changes, I'll do a test build
> > and then push out to the robots.
> 
> Thanks!  Looking at your following updated patch I found that your
> change from "pointer to const struct unwind_user_frame" to
> "const struct unwind_user_frame" (done for obvious reasons) will require
> unwind user sframe to undo this when refactoring unwind_user_next_fp()
> into unwind_user_next_common().  Would that be the usual procedure or
> could you leave it as "pointer to const struct unwind_user_frame" for
> now?

Ah, I see, that is here:

  https://lkml.kernel.org/r/20251022144326.4082059-9-jremus@linux.ibm.com

Yeah, just change it there. It is a bit weird to have this indirection
at this point.