linux-kernel - Re: [PATCH 2/2] perf tests: Add a test for the ARM 32-bit [vectors] page

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Date:   Thu, 25 Oct 2018 10:19:54 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Kim Phillips <kim.phillips@....com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        open list <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        rmk+kernel@...linux.org.uk, Ingo Molnar <mingo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiri Olsa <jolsa@...hat.com>, l.stach@...gutronix.de
Subject: Re: [PATCH 2/2] perf tests: Add a test for the ARM 32-bit [vectors]
 page

On 10/24/18 7:10 PM, Andrew Lunn wrote:
> On Wed, Oct 24, 2018 at 05:09:05PM -0700, Florian Fainelli wrote:
>> perf on ARM requires CONFIG_KUSER_HELPERS to be turned on to allow some
>> independance with respect to the ARM CPU being used. Add a test which
>> tries to locate the [vectors] page, created when CONFIG_KUSER_HELPERS is
>> turned on to help asses the system's health.
> 
> Hi Florian
> 
> I've suffered the pain from missing CONFIG_KUSER_HELPERS. The
> segfaults give little clue as to what is going wrong,and gdb is not
> much use either.

If you have a working backtrace, you can typically see the virtual
address being in 0xffff_xxxx which gives a bit of a clue, but yes, this
is not particularly helpful.

> 
> What i don't see here is any clue to CONFIG_KUSER_HELPERS. If the test
> fails, could you print a message suggesting CONFIG_KUSER_HELPERS on
> ARM?

Sure, sounds reasonable, thanks for taking a look.
-- 
Florian