linux-kernel - Re: [PATCH v2 1/6] powerpc/perf: Define big-endian version of perf_mem_data

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Date:   Mon, 6 Mar 2017 16:28:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
        Wang Nan <wangnan0@...wei.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Stephane Eranian <eranian@...gle.com>,
        Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2 1/6] powerpc/perf: Define big-endian version of
 perf_mem_data_src

On Mon, Mar 06, 2017 at 02:59:07PM +0000, David Laight wrote:
> From: Peter Zijlstra
> > Sent: 06 March 2017 11:22
> > To: Madhavan Srinivasan
> > Cc: Wang Nan; Alexander Shishkin; linux-kernel@...r.kernel.org; Arnaldo Carvalho de Melo; Alexei
> > Starovoitov; Ingo Molnar; Stephane Eranian; Sukadev Bhattiprolu; linuxppc-dev@...ts.ozlabs.org
> > Subject: Re: [PATCH v2 1/6] powerpc/perf: Define big-endian version of perf_mem_data_src
> > 
> > On Mon, Mar 06, 2017 at 04:13:08PM +0530, Madhavan Srinivasan wrote:
> > > From: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
> > >
> > > perf_mem_data_src is an union that is initialized via the ->val field
> > > and accessed via the bitmap fields. For this to work on big endian
> > > platforms, we also need a big-endian represenation of perf_mem_data_src.
> > 
> > Doesn't this break interpreting the data on a different endian machine?
> 
> Best to avoid bitfields if you ever care about the bit order.

Too late for that. But perf tool has quite a bit of code to muck fields
between different endians. With the full intent that generation on one
machine is readable by another.