Include file search path

[Robert Watson]

On Wed, 30 Mar 2011, Warner Losh wrote:

> On Mar 30, 2011, at 9:23 AM, Dimitry Andric wrote:
>> This is a rather nasty hack, though.  If we can make it work, we should 
>> probably try using --sysroot instead, or alternatively, -nostdinc and 
>> adding include dirs by hand.  The same for executable and library search 
>> paths, although I am not sure if there is a way to completely reset those 
>> with the current options.
>
> I'm pretty sure that the origins of this hack pre-dates the -sysroot feature 
> in gcc.  It works in -current and has for years, so nobody has cared enough 
> to even contemplate changing it.
>
> If you can make the sysroot feature work, that would be great, since that 
> would allow us to skip the compiler building phase if we were building using 
> external compilers.  I have some patches to make that work, but this very 
> problem is what I'd worked my way up to.  It works well if you are building 
> current on current, but not so well if you are mixing versions (you can mix 
> architectures if you are using the xdev feature I put in a while ago, but 
> even that has one or two niggles I need to iron out).

Count me as another eager consumer awaiting a nice answer to the general 
cross-compile problem.  I'm really looking for three things:

(1) A bit more intelligence from our build framework regarding not rebuilding
     the toolchain quite so many times!  I'd like to be able to do a buildworld
     with TARGET_ARCH with significantly improved performance.  Perhaps we can
     do this already, in which case a pointer considered welcome.

(2) Working clang/LLVM cross-compile of FreeBSD.  This seems like a basic
     requirement to adopt clang/LLVM, and as far as I'm aware that's not yet a
     resolved issue?

(3) Making it easy to plug in, first, an external gcc easily, and second, an
     external clang/LLVM.  One worrying point for me on the last one is that we
     can't yet build the whole kernel with clang/LLVM, at least for i386/amd64,
     so I guess you need both external gcc *and* external clang/LLVM?

We (Cambridge) are currently bringing up FreeBSD on a new soft-core 64-bit 
MIPS platform.  We're already using a non-base gcc for our boot loader work, 
and plan to move to using clang/LLVM later in the year.  The base system seems 
a bit short on detail when it comes to the above, currently.

Robert