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

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Message-ID: <5bdb1c91-8862-44b1-9f12-c5afa9e1806c@linux.ibm.com>
Date: Wed, 22 Oct 2025 16:55:01 +0200
From: Jens Remus <jremus@...ux.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
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

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?

https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=unwind/cleanup&id=f3624d64ba4862067b620fbd5bfbc0bfaf5368ae

Thanks and regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@...ibm.com

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