linux-kernel - Re: PAGE_ALIGN() compile breakage

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Date:	Fri, 25 Jul 2008 12:14:55 +0300
From:	Adrian Bunk <bunk@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andrea Righi <righi.andrea@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: PAGE_ALIGN() compile breakage

On Fri, Jul 25, 2008 at 01:55:37AM -0700, Andrew Morton wrote:
> On Fri, 25 Jul 2008 11:39:43 +0300 Adrian Bunk <bunk@...nel.org> wrote:
> 
> > Commit 27ac792ca0b0a1e7e65f20342260650516c95864
> > (PAGE_ALIGN(): correctly handle 64-bit values on 32-bit architectures)
> > causes on some architectures (e.g. avr32 and mips) compile errors
> > like the following in some configurations starting with:
> > 
> > <--  snip  -->
> > 
> > ...
> >   CC      init/main.o
> > In file included from 
> > /home/bunk/linux/kernel-2.6/git/linux-2.6/include/linux/utsname.h:35,
> >                  from /home/bunk/linux/kernel-2.6/git/linux-2.6/init/main.c:20:
> > /home/bunk/linux/kernel-2.6/git/linux-2.6/include/linux/sched.h: In function 'arch_pick_mmap_layout':
> > /home/bunk/linux/kernel-2.6/git/linux-2.6/include/linux/sched.h:2149: error: implicit declaration of function 'PAGE_ALIGN'
> > make[2]: *** [init/main.o] Error 1
> > 
> 
> pls test:
> 
> diff -puN include/linux/sched.h~a include/linux/sched.h
> --- a/include/linux/sched.h~a
> +++ a/include/linux/sched.h
> @@ -2139,16 +2139,7 @@ static inline void set_task_cpu(struct t
>  
>  #endif /* CONFIG_SMP */
>  
> -#ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
>  extern void arch_pick_mmap_layout(struct mm_struct *mm);
> -#else
> -static inline void arch_pick_mmap_layout(struct mm_struct *mm)
> -{
> -	mm->mmap_base = TASK_UNMAPPED_BASE;
> -	mm->get_unmapped_area = arch_get_unmapped_area;
> -	mm->unmap_area = arch_unmap_area;
> -}
> -#endif
>  
>  #ifdef CONFIG_TRACING
>  extern void
> diff -puN mm/mmap.c~a mm/mmap.c
> --- a/mm/mmap.c~a
> +++ a/mm/mmap.c
> @@ -2268,3 +2268,12 @@ int install_special_mapping(struct mm_st
>  
>  	return 0;
>  }
> +
> +#ifndef HAVE_ARCH_PICK_MMAP_LAYOUT
> +void arch_pick_mmap_layout(struct mm_struct *mm)
> +{
> +	mm->mmap_base = TASK_UNMAPPED_BASE;
> +	mm->get_unmapped_area = arch_get_unmapped_area;
> +	mm->unmap_area = arch_unmap_area;
> +}
> +#endif

Nice, this seems to fix the problem.

> > and more nasty problems follow later.
> > 
> > My suggestion is to:
> > - revert commit 27ac792ca0b0a1e7e65f20342260650516c95864 and then
> > - fix all PAGE_ALIGN() instances without moving them.
> 
> Every time this patch blew up (and it did it often), fixing it resulted
> in overall improvements.
> 
> > Unifying code is a good thing, but in this case it is not worth the 
> > trouble it causes by poking into the heart of our headers mess.
> 
> Well.   If we leave it a mess, it'll stay a mess.

An interesting question is whether the PAGE_ALIGN() move makes the mess 
bigger or smaller.

Ideally, all headers should be self-contained. IOW, they should #include 
everything they use.

But TASK_UNMAPPED_BASE in asm/processor.h on some architectures uses 
PAGE_ALIGN() that got moved from asm/page.h to linux/mm.h .

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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