linux-kernel - Re: [PATCH v4 12/39] unwind_user: Add frame pointer support

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Message-ID: <20250124181610.zdqvdaeqrp7kyzis@jpoimboe>
Date: Fri, 24 Jan 2025 10:16:10 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.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,
	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 12/39] unwind_user: Add frame pointer support

On Fri, Jan 24, 2025 at 09:59:37AM -0800, Andrii Nakryiko wrote:
> On Tue, Jan 21, 2025 at 6:32 PM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> >
> > Add optional support for user space frame pointer unwinding.  If
> > supported, the arch needs to enable CONFIG_HAVE_UNWIND_USER_FP and
> > define ARCH_INIT_USER_FP_FRAME.
> >
> > By encoding the frame offsets in struct unwind_user_frame, much of this
> > code can also be reused for future unwinder implementations like sframe.
> >
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> > ---
> >  arch/Kconfig                      |  4 +++
> >  include/asm-generic/unwind_user.h |  9 ++++++
> >  include/linux/unwind_user_types.h |  1 +
> >  kernel/unwind/user.c              | 49 +++++++++++++++++++++++++++++--
> >  4 files changed, 60 insertions(+), 3 deletions(-)
> >  create mode 100644 include/asm-generic/unwind_user.h
> >
> 
> Do you plan to reuse this logic for stack unwinding done by perf
> subsystem in perf_callchain_user()? See is_uprobe_at_func_entry()
> parts and also fixup_uretprobe_trampoline_entries() for some of the
> quirks that have to be taken into account when doing frame
> pointer-based unwinding. It would be great not to lose those in this
> new reimplementation.
> 
> Not sure what's the best way to avoid duplicating the logic, but I
> thought I'd bring that up.

Indeed!  That was on the todo list and somehow evaporated.

-- 
Josh