linux-kernel - Re: [PATCH v15 01/10] unwind_user: Add user space unwinding API with frame pointer support

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Message-ID: <20250728120847.0fd1c190@batman.local.home>
Date: Mon, 28 Jul 2025 12:08:47 -0400
From: Steven Rostedt <rostedt@...nel.org>
To: Jens Remus <jremus@...ux.ibm.com>
Cc: 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>, Arnaldo Carvalho de Melo <acme@...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: [PATCH v15 01/10] unwind_user: Add user space unwinding API
 with frame pointer support

On Mon, 28 Jul 2025 17:24:52 +0200
Jens Remus <jremus@...ux.ibm.com> wrote:

> 
> Reviewed-by: Jens Remus <jremus@...ux.ibm.com>

Thanks.

> 
> > diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c  
> 
> > +static int unwind_user_next_fp(struct unwind_user_state *state)
> > +{
> > +	struct unwind_user_frame *frame = &fp_frame;  
> 
> Optional: Pointer to const?

Hmm, yeah, and we can easily make fp_frame a constant as it's only
updated by the arch macro and never modified.

> 
> > +	unsigned long cfa, fp, ra = 0;  
> 
> Nit: Is initialization of ra really required?  I don't see where ra
> would be getting used without being set beforehand.

That's probably leftover.

These are minor changes, I'll update.

Thanks for the review.

-- Steve