linux-kernel - Re: [PATCH] fs: Cleanup string initializations (char[] instead of char *)

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Message-ID: <20140517165345.GG18016@ZenIV.linux.org.uk>
Date:	Sat, 17 May 2014 17:53:45 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Manuel Schölling <manuel.schoelling@....de>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: Cleanup string initializations (char[] instead of
 char *)

On Sat, May 17, 2014 at 05:00:18PM +0200, Manuel Schölling wrote:
> Initializations like 'char *foo = "bar"' will create two variables: a static
> string and a pointer (foo) to that static string. Instead 'char foo[] = "bar"'
> will declare a single variable and will end up in shorter
> assembly (according to Jeff Garzik on the KernelJanitor's TODO list).

The hell it will.  Compare assembler generated e.g. for 32bit x86 before
and after.

>  {
>  	char *dp;
>  	char *status = "disabled";
> -	const char * flags = "flags: ";
> +	const char flags[] = "flags: ";

The first variant puts address of constant array into local variable
(on stack or in a register).  The second one fills local _array_ - the
string itself goes on stack.
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