linux-kernel - Re: [PATCH] perf tools: add compatibility with libelf 0.8 and autodetect

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Message-ID: <20091024083031.GB20575@elte.hu>
Date:	Sat, 24 Oct 2009 10:30:31 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Lucas De Marchi <lucas.de.marchi@...il.com>
Cc:	Marti Raudsepp <marti@...fo.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tools: add compatibility with libelf 0.8 and
	autodetect


* Lucas De Marchi <lucas.de.marchi@...il.com> wrote:

> On Fri, Oct 23, 2009 at 19:48, Marti Raudsepp <marti@...fo.org> wrote:
> > On Sat, Oct 24, 2009 at 12:02 AM, Ingo Molnar <mingo@...e.hu> wrote:
> >> Mind doing a small change:
> >>
> >> I think we want a small cleanup here: a perf_elf_begin() wrapper in a
> >> header file to hide this #ifdef. (That's how Git wraps environmental
> >> libraries as well.)
> >
> Why don't you do something like?:
> 
> #ifdef LIBELF_NO_MMAP
> #define ELF_C_READ_MMAP ELF_C_READ
> #endif
> + changes to Makefile
> 
> or:
> 
> #ifndef ELF_C_READ_MMAP
> #define ELF_C_READ_MMAP ELF_C_READ
> #endif

Makes sense - i'd suggest to prefix it with PERF_ in that case, to make 
sure all callsites are aware of the wrapped nature of this constant. 

I.e. something like this:

/*
 * libelf 0.8 and earlier do not support ELF_C_READ_MMAP;
 * for newer versions we can use mmap to reduce memory usage:
 */
#ifndef ELF_C_READ_MMAP
# define PERF_ELF_C_READ_MMAP ELF_C_READ
#endif

	Ingo
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