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

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Message-ID: <CAORVsuUFzf3eBvMLWnJNdhYK4CHEvwNbSYNpOYOfNa5_enp7bA@mail.gmail.com>
Date:	Wed, 7 May 2014 09:40:30 +0200
From:	Jean Pihet <jean.pihet@...oldbits.com>
To:	Will Deacon <will.deacon@....com>
Cc:	Jean Pihet <jean.pihet@...aro.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	David Ahern <dsahern@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] perf tools: Add libdw DWARF post unwind support for ARM64

Hi Will,

On Tue, May 6, 2014 at 7:52 PM, Will Deacon <will.deacon@....com> wrote:
> 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,
My bad, I haven't checked carefully enough before replying.

Thx!
Jean
>
> Will
>
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