D target "layers" (was: D Cross Compiler)

[Iain Buclaw]

== Quote from Brendan Simon (eTRIX) (brendan.simon at etrix.com.au)'s article
> On 19/04/2011 5:00 AM, d.gnu-request at puremagic.com wrote:
> > From: Daniel Green<venix1 at gmail.com>
> > On 4/18/2011 5:15 AM, Kagamin wrote:
> >> >  Such feature would be fantastic.
> > I don't see this becoming a feature of D for quite some time if ever
> > although it would make the enforcement easier.
> > Once the subsets are defined the next challenge is enforcing them.  Two
> > ideas come to me right now.  Enforcing it by checking object symbols,
> > most restrictions would generate some form of standardized symbol
> > request.  The other is to use the D frontend and create a sort of lint
> > checker.
> I envisage a compiler switch to tell the compiler the target "layer" --
> bare, kernel, driver-low, driver-high, user ??
> The compiler would then produce a warning or error if certain language
> or run-time features are being used that is not suitable for the target
> layer.
> Maybe it can be a flexible system rather than hard coded into the
> compiler, such that there are config files that specify which language
> features are permissible or not.
> e.g. --target=bare, --target=kernel, --target=my-custom-target  (where
> my-custom-target[.cfg] is a file in standard location or filename)
> --target=~/D/configs/my-custom-target.cfg ???
> I'm sure the XOmB guys/gals (which I'm sure lurk on the various D lists)
> would have some good ideas and thoughts on this too.
> Just thinking out loud :)
> -- Brendan.

GCC already provides such equivalent options:

-fhosted   - Assert that compilation takes place in a hosted environment in which
the entire standard library is available. (reverse is -fno-hosted)

-ffreestanding - Assert that compilation takes place in a freestanding environment
in which the standard library may not exist, and program startup may not
necessarily be at "main". (reverse is -fno-freestanding)