Re: String literals in __init functions

From: Andrew Morton <akpm@linux-foundation.org>
To: Joe Perches <joe@perches.com>
Cc: gcc@gcc.gnu.org, Mathias Krause <minipli@googlemail.com>,
	Mason <slash.tmp@free.fr>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: String literals in __init functions
Date: Thu, 26 Mar 2015 15:15:57 -0700	[thread overview]
Message-ID: <20150326151557.61dfad84272aff10aaa4eba7@linux-foundation.org> (raw)
In-Reply-To: <1427407120.15849.34.camel@perches.com>

On Thu, 26 Mar 2015 14:58:40 -0700 Joe Perches <joe@perches.com> wrote:

> > I'd have thought that a function-wide
> > 	__attribute__((__string_section__(foo))
> > wouldn't be a ton of work to implement.
> 
> Maybe not.
> 
> Could some future version of gcc move string constants
> in a function to a specific section marked in a manner
> similar to what Andrew described above?

One thing which might complexicate this is

void foo()
{
	p("bar");
}

void  __attribute__((__string_section__(.init.rodata)) zot()
{
	p("bar");
}

It would be silly to create two instances of "bar".

Change it thusly:

#define __mark_str(str) \
	({ static const char var[] __attribute__((__section__(".init.string"))) = str; var; })

void foo()
{
	p("bar");
}

void zot()
{
	p(__mark_str("bar"));
}

and we indeed get two copies of "bar".

It would be nice not to do that, but I guess that losing this
optimization is a reasonable compromise.