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

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Message-ID: <CAEf4BzbG3C5=8bB0DKrVdMHDxADbZxnAwku46QAqt8qLW6ngOA@mail.gmail.com>
Date: Fri, 24 Jan 2025 09:59:28 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
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, 
	Jens Remus <jremus@...ux.ibm.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>
Subject: Re: [PATCH v4 11/39] unwind_user: Add user space unwinding API

On Tue, Jan 21, 2025 at 6:32 PM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
>
> Introduce a generic API for unwinding user stacks.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
>  arch/Kconfig                      |  3 ++
>  include/linux/unwind_user.h       | 15 ++++++++
>  include/linux/unwind_user_types.h | 31 ++++++++++++++++
>  kernel/Makefile                   |  1 +
>  kernel/unwind/Makefile            |  1 +
>  kernel/unwind/user.c              | 59 +++++++++++++++++++++++++++++++
>  6 files changed, 110 insertions(+)
>  create mode 100644 include/linux/unwind_user.h
>  create mode 100644 include/linux/unwind_user_types.h
>  create mode 100644 kernel/unwind/Makefile
>  create mode 100644 kernel/unwind/user.c
>

[...]

> --- /dev/null
> +++ b/kernel/unwind/user.c
> @@ -0,0 +1,59 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> +* Generic interfaces for unwinding user space
> +*/
> +#include <linux/kernel.h>
> +#include <linux/sched.h>
> +#include <linux/sched/task_stack.h>
> +#include <linux/unwind_user.h>
> +
> +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;

wouldn't all the above generate compilation warnings about unused
variables, potentially breaking bisection?

> +
> +       /* no implementation yet */
> +       -EINVAL;

return missing?

> +}

[...]