Re: [2.6 patch] Use -ffreestanding? (fwd)

[Adrian Bunk <bunk@stusta.de>]

On Sun, Nov 21, 2004 at 10:10:28PM -0800, Linus Torvalds wrote:
> 
> 
> On Mon, 22 Nov 2004, Adrian Bunk wrote:
> > 
> > for the kernel, it would be logical to use -ffreestanding. The kernel is 
> > not a hosted environment with a standard C library.
> > 
> > Linus agreed that it would make sense.
> 
> Note that while I agree that it sounds sensible, it would be good to have 
> somebody specify exactly what changes from the use of "-ffreestanding".
> 
> I _assume_ that all the things that gcc takes for granted are things that 
> Linux already has its own definitions for, and that -ffreestanding doesn't 
> actually change anything for at least the regular architectures. But if 
> there is any object code changes, can you check those out and explain 
> them?

Andi Kleen reported:
  Newer gcc rewrites sprintf(buf,"%s",str) to strcpy(buf,str) transparently.

This is only true with unit-at-a-time (disabled on i386 but enabled
on x86_64). The Linux kernel doesn't offer a standard C library, and 
such transparent replacements of kernel functions with builtins are 
quite fragile.

Even with -ffreestanding, it's still possilble to explicitely use a gcc 
builtin if desired.

> 		Linus

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