Re: [PATCH] Fix sh4 build with __ASSUME_ST_INO_64_BIT redefinition

[Joseph Myers <joseph@codesourcery.com>]

On Wed, 9 Nov 2016, Adhemerval Zanella wrote:

> It is because sh4 kernel-features.sh is included multiple times
> without guards and this patch fixes by adding them. Tested on a
> sh4-linux-gnu build.
> 
> Also with this issues, is there are strong reason to *not* have include guards
> on kernel-features.h?  With current approach, a architecture can't include
> Linux default kernel-features.h and redefine it to a different value, only
> undefine it (unless it explicit do not include default kernel-features.h,
> and I think that's is not the idea).
> 
> 	* sysdeps/unix/sysv/linux/sh/kernel-features.h: Add include
> 	guards.

OK.  I think it's appropriate for all these headers to have include 
guards.

The #ifndef, #undef etc. could be avoided (moving this header closer to 
glibc's macro-name-typo-proof norms in this regard) if the header were 
split up into smaller pieces for individual macros or groups of related 
macros whenever a macro's definition needs to vary between architectures.  
Thus, you'd have e.g. kernel-features-st-ino.h defining 
__ASSUME_ST_INO_64_BIT to either 0 or 1, the default version of that 
header would define to 0 and the architectures overriding it would define 
to 1 (and wouldn't need #include_next).  kernel-features.h could end up as 
an architecture-independent header that just #includes the smaller 
architecture-specific headers.  (This is not a full design, especially for 
the more complicated cases such as socket syscalls.)

-- 
Joseph S. Myers
joseph@codesourcery.com