linux-kernel - Re: [PATCH 3/5] perf tools: Add GCC optimization to memory allocating functions

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Date:	Fri, 26 Nov 2010 22:30:40 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, Davidlohr Bueso <dave@....org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 3/5] perf tools: Add GCC optimization to memory
	allocating functions

Em Fri, Nov 26, 2010 at 07:47:19PM -0200, Arnaldo Carvalho de Melo escreveu:
> From: Davidlohr Bueso <dave@....org>
> 
> We can benefit from the alloc_size attribute in xrealloc and zalloc.
> 
> Quoting from http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html:
> 
> "The alloc_size attribute is used to tell the compiler that the function return
> value points to memory, where the size is given by one or two of the functions
> parameters. GCC uses this information to improve the correctness of
> __builtin_object_size."

Ingo, please don't pull this, it breaks the build with older GCCs...

util/util.h:185: warning: ‘alloc_size’ attribute directive ignored
util/util.h:190: warning: ‘alloc_size’ attribute directive ignored
make: *** [/home/acme/git/build/perf/builtin-annotate.o] Error 1
make: Leaving directory `/home/acme/git/linux-2.6-tip/tools/perf'
[acme@...a linux-2.6-tip]$ gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-libgcj-multifile
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada
--enable-java-awt=gtk --disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre
--with-cpu=generic --host=x86_64-redhat-linux
Thread model: posix
gcc version 4.1.2 20071124 (Red Hat 4.1.2-42)

I'll reorg this using compiler.h tricks probably, for now I'll just
remove it from my perf/core branch.

- Arnaldo
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