On Fri, 23 Jul 2010, Richard Guenther wrote:

> > Err.. I'm not sure quite what you're talking about.
> >
> > native:
> > #include "..." search starts here:
> > #include <...> search starts here:
> >  /usr/local/include
> >  /usr/lib/gcc/x86_64-redhat-linux/4.4.4/include
> >  /usr/include
> > End of search list.
> >
> > cross+sysroot:
> > #include "..." search starts here:
> > #include <...> search starts here:
> >  /local/rth/gcc/run-axp/lib/gcc/alphaev67-linux/4.6.0/include
> >  /local/rth/gcc/run-axp/lib/gcc/alphaev67-linux/4.6.0/include-fixed
> >  /local/rth/gcc/run-axp/lib/gcc/alphaev67-linux/4.6.0/../../../../alphaev67-linux/include
> >  /local/rth/gcc/run-axp/alphaev67-linux/sys-root/usr/include
> > End of search list.
> >
> > In both cases gcc-include preceeds the system-include dir.
> > The only difference is that native also searches local-include
> > (although I can't tell you why that preceeds gcc-include).
> 
> I wondered about this myself, but it is even documented this way
> in cpp.texi ...
> 
> It seems that there is no local include dir for cross+sysroot.
> 
> I'm sure Joseph knows why?

My guess would be that the ordering predates the separation of include and 
include-fixed.  /usr/local/include was meant to be headers that are known 
to work with GCC (as opposed to /usr/include, the headers originally for 
use with a proprietary non-GNU compiler) and so (a) didn't need fixed 
versions of headers and (b) was meant to go before system headers and 
override them in the case of local GNU libraries replacing pieces of 
system functionality.

Now, I'd think what's logical would be the GCC include directory, then 
system headers including both /usr/local/include and /usr/include and 
putting fixed versions of a directory immediately before that directory.  
But since we only have fixed headers for /usr/include, that means include, 
/usr/local/include, include-fixed, /usr/include.  In a sysroot 
configuration, $sysroot/usr/local/include ought to be searched; I see no 
reason for it not to be and searching it improves consistency with what is 
searched in the native case.

-- 
Joseph S. Myers
joseph@codesourcery.com