linux-kernel - Re: [PATCH 03/22] tools lib traceevent: Add traceevent_host

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Date:	Sat, 23 Nov 2013 03:27:08 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 03/22] tools lib traceevent: Add
 traceevent_host_bigendian function

On Fri, 22 Nov 2013 23:22:52 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> 2013-11-21 (목), 12:01 +0100, Jiri Olsa:
> > Adding traceevent_host_bigendian function to get host
> > endianity. It's used in following patches.
> 
> [SNIP]
> > +static inline int traceevent_host_bigendian(void)
> > +{
> > +	unsigned char str[] = { 0x1, 0x2, 0x3, 0x4 };
> > +	unsigned int *ptr;
> > +
> > +	ptr = (unsigned int *)str;
> > +	return *ptr == 0x01020304;
> 
> Is it safe for every architecture supported - especially ones that
> require stricter alignment?  I know many architectures/compilers align
> stack but not sure doing this is safe for all architecture.

Would you prefer this (I tested it on both a big and little endian)

{
	unsigned char str[] = { 0x1, 0x2, 0x3, 0x4 };
	unsigned int val;

	memcpy(&val, str, 4);
	return val == 0x01020304;
}

-- Steve

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