linux-kernel - Re: [PATCH v3 08/19] unwind/x86: Enable CONFIG_HAVE_UNWIND_USER

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Message-ID: <20241029180838.GF14555@noisy.programming.kicks-ass.net>
Date: Tue, 29 Oct 2024 19:08:38 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.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.kerne.org,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Jens Remus <jremus@...ux.ibm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v3 08/19] unwind/x86: Enable CONFIG_HAVE_UNWIND_USER_FP

On Tue, Oct 29, 2024 at 09:31:10AM -0700, Josh Poimboeuf wrote:
> On Tue, Oct 29, 2024 at 02:13:03PM +0100, Peter Zijlstra wrote:

> > > +#define ARCH_INIT_USER_FP_FRAME							\
> > > +	.ra_off		= (s32)sizeof(long) * -1,				\
> > > +	.cfa_off	= (s32)sizeof(long) * 2,				\
> > > +	.fp_off		= (s32)sizeof(long) * -2,				\
> > > +	.use_fp		= true,
> > > +
> > > +#endif /* _ASM_X86_UNWIND_USER_H */
> > 
> > What about compat / 32bit userspace?
> 
> Sframe doesn't support 32-bit binaries at the moment.  Does anybody
> actually care?

Dunno, I think the only 32bit code I've recently ran is in selftests and
wine32 -- because Monkey Island rules :-)

> You're right this regresses existing perf behavior for the frame pointer
> case.  I'll try to fix that.

Thanks, this patch is the frame pointer unwinder, that really should do
32bit.