linux-kernel - Re: [PATCH v12 01/14] unwind_user: Add user space unwinding API

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Message-ID: <12c620ea-4bee-4019-8143-8ecbaeeafc11@efficios.com>
Date: Fri, 4 Jul 2025 14:20:54 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...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>, Jens Remus
 <jremus@...ux.ibm.com>, Linus Torvalds <torvalds@...ux-foundation.org>,
 Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>,
 Florian Weimer <fweimer@...hat.com>
Subject: Re: [PATCH v12 01/14] unwind_user: Add user space unwinding API

On 2025-06-30 20:53, Steven Rostedt wrote:
> From: Josh Poimboeuf <jpoimboe@...nel.org>
> 
> Introduce a generic API for unwinding user stacks.
> 
> In order to expand user space unwinding to be able to handle more complex
> scenarios, such as deferred unwinding and reading user space information,
> create a generic interface that all architectures can use that support the
> various unwinding methods.
> 
> This is an alternative method for handling user space stack traces from
> the simple stack_trace_save_user() API. This does not replace that
> interface, but this interface will be used to expand the functionality of
> user space stack walking.
> 
> None of the structures introduced will be exposed to user space tooling.

Would it be possible to make those unwind APIs EXPORT_SYMBOL_GPL
so they are available for GPL kernel modules ?

Thanks,

Mathieu

> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>   MAINTAINERS                       |  8 +++++
>   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              | 55 +++++++++++++++++++++++++++++++
>   7 files changed, 114 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
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 4bac4ea21b64..ed5705c4f7d9 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -25924,6 +25924,14 @@ F:	Documentation/driver-api/uio-howto.rst
>   F:	drivers/uio/
>   F:	include/linux/uio_driver.h
>   
> +USERSPACE STACK UNWINDING
> +M:	Josh Poimboeuf <jpoimboe@...nel.org>
> +M:	Steven Rostedt <rostedt@...dmis.org>
> +S:	Maintained
> +F:	include/linux/unwind*.h
> +F:	kernel/unwind/
> +
> +
>   UTIL-LINUX PACKAGE
>   M:	Karel Zak <kzak@...hat.com>
>   L:	util-linux@...r.kernel.org
> diff --git a/arch/Kconfig b/arch/Kconfig
> index a3308a220f86..ea59e5d7cc69 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -435,6 +435,9 @@ config HAVE_HARDLOCKUP_DETECTOR_ARCH
>   	  It uses the same command line parameters, and sysctl interface,
>   	  as the generic hardlockup detectors.
>   
> +config UNWIND_USER
> +	bool
> +
>   config HAVE_PERF_REGS
>   	bool
>   	help
> diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h
> new file mode 100644
> index 000000000000..aa7923c1384f
> --- /dev/null
> +++ b/include/linux/unwind_user.h
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_UNWIND_USER_H
> +#define _LINUX_UNWIND_USER_H
> +
> +#include <linux/unwind_user_types.h>
> +
> +int unwind_user_start(struct unwind_user_state *state);
> +int unwind_user_next(struct unwind_user_state *state);
> +
> +int unwind_user(struct unwind_stacktrace *trace, unsigned int max_entries);
> +
> +#define for_each_user_frame(state) \
> +	for (unwind_user_start((state)); !(state)->done; unwind_user_next((state)))
> +
> +#endif /* _LINUX_UNWIND_USER_H */

[...]


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com