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

Peter Zijlstra
2017-03-06T15:29:30Z

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@vger.kernel.org; Arnaldo Carvalho de Melo; Alexei
> > Starovoitov; Ingo Molnar; Stephane Eranian; Sukadev Bhattiprolu; linuxppc-dev@lists.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@linux.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.