linux-kernel - Re: [PATCH 3/3] perf tools: Add libdw DWARF post unwind support for ARM64

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Message-ID: <20140506175216.GG13677@arm.com>
Date:	Tue, 6 May 2014 18:52:16 +0100
From:	Will Deacon <will.deacon@....com>
To:	Jean Pihet <jean.pihet@...aro.org>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 3/3] perf tools: Add libdw DWARF post unwind support for
 ARM64

On Tue, May 06, 2014 at 06:41:55PM +0100, Jean Pihet wrote:
> Hi Will,
> 
> On 6 May 2014 19:00, Will Deacon <will.deacon@....com> wrote:
> > Hi Jean,
> >
> > On Tue, May 06, 2014 at 04:55:33PM +0100, Jean Pihet wrote:
> >> Adding libdw DWARF post unwind support, which is part
> >> of elfutils-devel/libdw-dev package from version 0.158.
> >>
> >> Note: the libdw code needs some support for dwarf unwinding
> >> on ARM64, this code is submitted seperately on the elfutils
> >> ML.
> >>
> >> The new code is contained in unwin-libdw.c object, and
> >> implements unwind__get_entries unwind interface function.
> >
> > Are you planning to implement support for 32-bit ARM too? If so, we'll need
> > compat handling here again (your favourite!).
> Yes! Another patch set (sent just before this one) targets ARM. There
> is a nice ToDo in the cover letter: handle compat mode correctly. In
> fact I sent a patch to libdw, so it supports it already but is
> somewhat broken for compat mode. This is on my prefered ToDo list ;-)
> 
> >
> >> +bool libdw__arch_set_initial_registers(Dwfl_Thread *thread, void *arg)
> >> +{
> >> +     struct unwind_info *ui = arg;
> >> +     struct regs_dump *user_regs = &ui->sample->user_regs;
> >> +     Dwarf_Word dwarf_regs[PERF_REG_ARM64_MAX];
> >
> > Shouldn't this be PERF_REG_ARM64_MAX - 1?
> Ah, well spotted! I will change although it shouldn't harm, right?

Actually, looking again, I think I'm wrong and your code was right first
time! It looks like dwfl_thread_state_registers takes the limit too, so I
don't think you need to change anything (except for adding compat support).

Sorry about that,

Will
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