linux-kernel - Re: [PATCH] NTFS: Change string pointers to string constants.

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Date:	Wed, 9 Dec 2009 15:59:05 +0100
From:	Marcin Slusarz <marcin.slusarz@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Anton Altaparmakov <aia21@....ac.uk>,
	John Daiker <daikerjohn@...il.com>,
	kernel-janitors@...r.kernel.org, aia21@...tab.net,
	linux-ntfs-dev@...ts.sourceforge.net,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] NTFS: Change string pointers to string constants.

On Mon, Dec 07, 2009 at 05:47:13PM -0800, Joe Perches wrote:
> On Tue, 2009-12-08 at 00:57 +0000, Anton Altaparmakov wrote:
> > Can you please explain the rational for making this change?
> 
> Perhaps it's not worth much, but it saves a pointer reference.
> 
> $ cat pointer.c
> #include <string.h>
> #include <stdio.h>
> 
> int main (int argc, char** argv)
> {
> 	static const char *foo = "abcdefg";
> 	printf("%s\n", foo);
> 	return 0;
> }
> 
> $ gcc -c pointer.c
> $ size pointer.o
>    text	   data	    bss	    dec	    hex	filename
>      37	      4	      0	     41	     29	pointer.o
> 
> $ cat reference.c
> #include <string.h>
> #include <stdio.h>
> 
> int main (int argc, char** argv)
> {
> static const char foo[] = "abcdefg";
> printf("%s\n", foo);
> return 0;
> }
> 
> $ gcc -c reference.c
> $ size reference.o
>    text    data     bss     dec     hex filename
>      36       0       0      36      24 reference.o

Yeah, for static variables it's better. But for automatic variables
it's worse, because it now has to do a copy at runtime.
And the patch changes both types.

$ size pointer.o reference.o
   text    data     bss     dec     hex filename
    101       8       0     109      6d pointer.o
     96       0       0      96      60 reference.o

$ size pointer-nonstatic.o reference-nonstatic.o
   text    data     bss     dec     hex filename
    106       0       0     106      6a pointer-nonstatic.o
    109       0       0     109      6d reference-nonstatic.o
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