linux-kernel - Re: [PATCH v4 11/39] unwind_user: Add user space unwinding API

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Message-ID: <20250124170921.oa5etcxie3axy6jk@jpoimboe>
Date: Fri, 24 Jan 2025 09:09:21 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Jens Remus <jremus@...ux.ibm.com>
Cc: x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	linux-toolchains@...r.kernel.org, Jordan Rome <jordalgo@...a.com>,
	Sam James <sam@...too.org>, linux-trace-kernel@...r.kernel.org,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Weinan Liu <wnliu@...gle.com>, Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH v4 11/39] unwind_user: Add user space unwinding API

On Fri, Jan 24, 2025 at 05:41:29PM +0100, Jens Remus wrote:
> On 22.01.2025 03:31, Josh Poimboeuf wrote:
> > +int unwind_user_next(struct unwind_user_state *state)
> > +{
> > +	struct unwind_user_frame _frame;
> > +	struct unwind_user_frame *frame = &_frame;
> > +	unsigned long cfa = 0, fp, ra = 0;
> 
> Why are cfa and ra initialized to zero? Where is that important in
> subsequent patches?
> 
> "[PATCH v4 12/39] unwind_user: Add frame pointer support" does either
> unconditionally set both cfa and ra or bail out.

Right, probably leftovers from some previous iteration.  I drop those.

-- 
Josh