Re: 2.6.25-rc8-mm1 (mips build failure)

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 2 Apr 2008 10:33:32 -0700 (PDT)
Christoph Lameter <clameter@sgi.com> wrote:

> On Tue, 1 Apr 2008, Andrew Morton wrote:
> 
> > On Wed, 02 Apr 2008 09:40:22 +0400 Dmitri Vorobiev <dmitri.vorobiev@gmail.com> wrote:
> > 
> > > Hi Andrew,
> > > 
> > > MIPS build fails with the following:
> > > 
> > > $ make ARCH=mips CROSS_COMPILE=mips-unknown-linux-gnu-
> > > ...
> > > [skipped]
> > > ...
> > >   CC      arch/mips/mips-boards/generic/init.o
> > > In file included from include/asm/cacheflush.h:13,
> > >                  from arch/mips/mips-boards/generic/init.c:30:
> > > include/linux/mm.h:411:63: "NR_PAGEFLAGS" is not defined
> > > include/linux/mm.h:459:62: "NR_PAGEFLAGS" is not defined
> > > make[1]: *** [arch/mips/mips-boards/generic/init.o] Error 1
> > > make: *** [arch/mips/mips-boards/generic] Error 2
> > 
> > ahh, yup, known problem, sorry.  We are slowly working on a fix.
> 
> This the fix that I posted a couple of days ago after Andrew noted the 
> problem:
> 
> 
> 
> 
> From: Christoph Lameter <clameter@sgi.com>
> Subject: Allow override of definition for asm constant
> 
> MIPS has a different way of defining asm constants which causes troubles
> for bounds.h generation (see also the Kbuild script).
> 
> Add a new per arch CONFIG variable
> 
> 	CONFIG_ASM_SYMBOL_PREFIX
> 
> which can be set to define an alternate header for asm constant definitions.
> Use this for MIPS to make bounds determination work right.
> 
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
> 
> ---
>  arch/mips/Kconfig |    7 +++++++
>  kernel/bounds.c   |   11 ++++++++++-
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6.25-rc5-mm1/arch/mips/Kconfig
> ===================================================================
> --- linux-2.6.25-rc5-mm1.orig/arch/mips/Kconfig	2008-03-31 13:14:26.888383587 -0700
> +++ linux-2.6.25-rc5-mm1/arch/mips/Kconfig	2008-03-31 13:14:28.028403612 -0700
> @@ -2019,6 +2019,13 @@ config I8253
>  config ZONE_DMA32
>  	bool
>  
> +#
> +# Used to override gas symbol setup in kernel/bounds.c.
> +#
> +config ASM_SYMBOL_PREFIX
> +	string
> +	default "@@@#define "
> +
>  source "drivers/pcmcia/Kconfig"
>  
>  source "drivers/pci/hotplug/Kconfig"
> Index: linux-2.6.25-rc5-mm1/kernel/bounds.c
> ===================================================================
> --- linux-2.6.25-rc5-mm1.orig/kernel/bounds.c	2008-03-31 13:14:26.904383870 -0700
> +++ linux-2.6.25-rc5-mm1/kernel/bounds.c	2008-03-31 13:14:28.028403612 -0700
> @@ -9,8 +9,17 @@
>  #include <linux/page-flags.h>
>  #include <linux/mmzone.h>
>  
> +#ifdef CONFIG_ASM_SYMBOL_PREFIX
> +#define PREFIX CONFIG_ASM_SYMBOL_PREFIX
> +#else
> +/*
> + * Standard gas way of defining an asm symbol
> + */
> +#define PREFIX "->"
> +#endif
> +
>  #define DEFINE(sym, val) \
> -	asm volatile("\n->" #sym " %0 " #val : : "i" (val))
> +	asm volatile("\n" PREFIX #sym " %0 " : : "i" (val))
>  
>  #define BLANK() asm volatile("\n->" : :)
>  

I'm obviously missing something here.

i386 generates

->NR_PAGEFLAGS $18 __NR_PAGEFLAGS       #

mips generates

->NR_PAGEFLAGS 18 __NR_PAGEFLAGS         #

The only difference is the "$".  This can be trivially handled in the sed
expression which filters this .s file.

Why are we diddling with that "->" thing, and why does it even exist?