linux-kernel - Re: [2.6 patch] re-add -ffreestanding

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Message-ID: <20060907010235.GE25473@stusta.de>
Date:	Thu, 7 Sep 2006 03:02:35 +0200
From:	Adrian Bunk <bunk@...sta.de>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	Andi Kleen <ak@...e.de>, Andrew Morton <akpm@...l.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [2.6 patch] re-add -ffreestanding

On Thu, Sep 07, 2006 at 02:47:42AM +0200, Roman Zippel wrote:
> Hi,
> 
> On Thu, 7 Sep 2006, Adrian Bunk wrote:
> 
> > > BS, even without it gcc can't make such assumption.
> > > There is not a single optimization, which would be invalid in a kernel 
> > > environment and would be "fixed" by this option, so please stop this 
> > > nonsense.
> > 
> > You are wrong.
> > 
> > Section 5.1.2.2.2 of ISO/IEC 9899:1999 says:
> > In a hosted environment, a program may use all functions, macros, type 
> > definitions, and objects described in the library clause (clause 7).
> > 
> > Since a hosted environment means gcc+libc, it's therefore clear that gcc 
> > can assume the presence of a full libc if gcc isn't told that it's used 
> > as a freestanding environment.
> 
> Define "full libc".

Everything described in clause 7 of ISO/IEC 9899:1999.

> Explain what exactly -ffreestanding fixes, which is not valid for the 
> kernel.

It's simply correct since the kernel doesn't provide everything 
described in clause 7 of ISO/IEC 9899:1999.

And it fixes compile errors caused by the fact that gcc is otherwise 
allowed to replace calls to any standard C function with semantically 
equivalent calls to other standard C functions - in a hosted environment 
the latter are guaranteed to be present.

> byem Roman

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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