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Date: Thu, 3 Oct 2013 08:27:25 -0700
From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
To: Michael Ellerman <michael@ellerman.id.au>
Subject: Re: [PATCH 6/9][v5] powerpc/perf: Define big-endian version of
 perf_mem_data_src
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Cc: Michael Ellerman <michaele@au1.ibm.com>, linux-kernel@vger.kernel.org,
 Stephane Eranian <eranian@google.com>, linuxppc-dev@ozlabs.org,
 Paul Mackerras <paulus@samba.org>,
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Michael Ellerman [michael@ellerman.id.au] wrote:
| On Tue, Oct 01, 2013 at 05:15:07PM -0700, Sukadev Bhattiprolu wrote:
| > 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.
| > 
| > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
| > index ca1d90b..846f399 100644
| > --- a/include/uapi/linux/perf_event.h
| > +++ b/include/uapi/linux/perf_event.h
| > @@ -19,6 +19,50 @@
| >  #include <asm/byteorder.h>
| >  
| >  /*
| > + * Kernel and userspace check for endianness in incompatible ways.
| > + * In user space, <endian.h> defines both __BIG_ENDIAN and __LITTLE_ENDIAN
| > + * but sets __BYTE_ORDER to one or the other. So user space uses checks are:
| 
| 
| Why can't you use __BIG_ENDIAN_BITFIELD ?

BTW, any clues on why there are so many different ways of checking endianness ?

Any standards related stuff or just evolution ?

Sukadev