about __BITS_PER_LONG

about __BITS_PER_LONG

[Guan Xuetao]

Hi, Arnd:

  When using asm-generic/bitsperlong.h, I think that __BITS_PER_LONG could be the
same as BITS_PER_LONG if-not-defined. And this could avoid the duplicated macros
in almost all architectures.

Regards.

Guan Xuetao

---
diff --git a/include/asm-generic/bitsperlong.h b/include/asm-generic/bitsperlong.h
index 4ae54e0..31d032a 100644
--- a/include/asm-generic/bitsperlong.h
+++ b/include/asm-generic/bitsperlong.h
@@ -9,7 +9,11 @@
  * to decide it, but rather check a compiler provided macro.
  */
 #ifndef __BITS_PER_LONG
-#define __BITS_PER_LONG 32
+#   ifdef CONFIG_64BIT
+#	define __BITS_PER_LONG 64
+#   else
+#	define __BITS_PER_LONG 32
+#   endif /* CONFIG_64BIT */
 #endif
 
 #ifdef __KERNEL__

about __BITS_PER_LONG

[Guan Xuetao]

Hi, Arnd:

  When using asm-generic/bitsperlong.h, I think that __BITS_PER_LONG could be the
same as BITS_PER_LONG if-not-defined. And this could avoid the duplicated macros
in almost all architectures.

Regards.

Guan Xuetao

---
diff --git a/include/asm-generic/bitsperlong.h b/include/asm-generic/bitsperlong.h
index 4ae54e0..31d032a 100644
--- a/include/asm-generic/bitsperlong.h
+++ b/include/asm-generic/bitsperlong.h
@@ -9,7 +9,11 @@
  * to decide it, but rather check a compiler provided macro.
  */
 #ifndef __BITS_PER_LONG
-#define __BITS_PER_LONG 32
+#   ifdef CONFIG_64BIT
+#	define __BITS_PER_LONG 64
+#   else
+#	define __BITS_PER_LONG 32
+#   endif /* CONFIG_64BIT */
 #endif
 
 #ifdef __KERNEL__

Re: about __BITS_PER_LONG

[Arnd Bergmann]

On Monday 11 April 2011, Guan Xuetao wrote:
> --- a/include/asm-generic/bitsperlong.h
> +++ b/include/asm-generic/bitsperlong.h
> @@ -9,7 +9,11 @@
>   * to decide it, but rather check a compiler provided macro.
>   */
>  #ifndef __BITS_PER_LONG
> -#define __BITS_PER_LONG 32
> +#   ifdef CONFIG_64BIT
> +#      define __BITS_PER_LONG 64
> +#   else
> +#      define __BITS_PER_LONG 32
> +#   endif /* CONFIG_64BIT */
>  #endif
>  

Unfortunately, this does not work, because the __BITS_PER_LONG definition is meant
for user space. You have to make this depend on a preprocessor macro that
is provided by the compiler based on the command line switches (e.g. -m64) that
a use could pass to the compiler.

In user space, the CONFIG_* symbols are meaningless.

	Arnd

RE: about __BITS_PER_LONG

[Guan Xuetao]

> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@arndb.de]
> Sent: Monday, April 11, 2011 11:25 PM
> To: Guan Xuetao
> Cc: linux-kernel@vger.kernel.org; linux-arch@vger.kernel.org
> Subject: Re: about __BITS_PER_LONG
> 
> On Monday 11 April 2011, Guan Xuetao wrote:
> > --- a/include/asm-generic/bitsperlong.h
> > +++ b/include/asm-generic/bitsperlong.h
> > @@ -9,7 +9,11 @@
> >   * to decide it, but rather check a compiler provided macro.
> >   */
> >  #ifndef __BITS_PER_LONG
> > -#define __BITS_PER_LONG 32
> > +#   ifdef CONFIG_64BIT
> > +#      define __BITS_PER_LONG 64
> > +#   else
> > +#      define __BITS_PER_LONG 32
> > +#   endif /* CONFIG_64BIT */
> >  #endif
> >
> 
> Unfortunately, this does not work, because the __BITS_PER_LONG definition is meant
> for user space. You have to make this depend on a preprocessor macro that
> is provided by the compiler based on the command line switches (e.g. -m64) that
> a use could pass to the compiler.
However,  there is no conflict between the definition depending on a preprocessor macro and 
the definition of asm-generic header.

> 
> In user space, the CONFIG_* symbols are meaningless.
Yes, that's the problem. I have not notice it before.
So, only one value can be reserved in such circumstances.

> 
> 	Arnd

Thanks & Regards.

Guan Xuetao