FAQ - Why sparse?

Q.  Why not just use gcc?

A.  Gcc is big, complex, and the gcc maintainers are not interested in
    other uses of the gcc front-end.  In fact, gcc has explicitly
    resisted splitting up the front and back ends and having some common
    intermediate language because or religious license issues - you can
    have multiple front ends and back ends, but they all have to be part
    of gcc and licensed under the GPL. 

    This all (in my opinion) makes gcc development harder than it should
    be, and makes the end result very ungainly.  With "sparse", the
    front-end is very explicitly separated into its own independent
    project, and is totally independent from the users.  I don't want to
    know what you do in the back-end, because I don't think I _should_
    know or care. 


Q.  Why not GPL?

A.  See the previous question: I personally think that the front end
    must be a totally separate project from the back end: any other
    approach just leads to insanity.  However, at the same time clearly
    we cannot write intermediate files etc crud (since then the back end
    would have to re-parse the whole thing and would have to have its
    own front end and just do a lot of things that do not make any sense
    from a technical standpoint).

    I like the GPL, but as rms says, "Linus is just an engineer". I
    refuse to use a license if that license causes bad engineering
    decisions.  I want the front-end to be considered a separate
    project, yet the GPL considers the required linking to make the
    combined thing a derived work. Which is against the whole point
    of 'sparse'.

    I'm not interested in code generation. I'm not interested in what
    other people do with their back-ends.  I _am_ interested in making a
    good front-end, and "good" means that people find it usable. And
    they shouldn't be scared away by politics or licenses. If they want
    to make their back-end be BSD/MIT licensed, that's great. And if
    they want to have a proprietary back-end, that's ok by me too. It's
    their loss, not mine.

    At the same time, I'm a big believer in "quid pro quo". I wrote the
    front-end, and if you make improvements to the semantic parsing part
    (as opposed to just using the resulting parse tree), you'd better
    cough up.  The front-end is intended to be an open-source project in
    its own right, and if you improve the front end, you must give those
    improvements back. That's your "quid" to my "quo".


Q.  So what _is_ the license?

A.  I don't know yet.  I originally thought it would be LGPL, but I'm
    possibly going for a license that is _not_ subsumable by the GPL. 
    In other words, I don't want to see a GPL'd project suck in the
    LGPL'd front-end, and then make changes to the front end under the
    GPL (this is something that the LGPL expressly allows, and see the
    previous question for why I think it's the _only_ thing that I will
    not allow). 

    The current front-runner is the OSL ("Open Software License", see
    http://www.opensource.org/licenses/osl.php), together with a note on
    what makes source derivative and what does not to make it clear that
    people can write back-ends for it without having to make those
    back-ends available under the OSL. 


Q.  Does it really parse C?

A.  Yeah, well...  It parses a fairly complete subset of "extended C" as
    defined by gcc.  HOWEVER, since I don't believe in K&R syntax for
    function declarations or in giving automatic integer types, it
    doesn't do that.  If you don't give types to your variables, they
    won't have any types, and you can't use them.

    Similarly, it will be very unhappy about undeclared functions,
    rather than just assuming they have type "int". 

    Note that a large rationale for me doing this project is for type
    following, which to some degree explains why the thing is type-anal
    and refuses to touch the old-style pre-ANSI non-typed (or weakly
    typed) constructs. Maybe somebody else who is working on projects
    where pre-ANSI C makes sense might be more inclined to care about
    ancient C.  It's open source, after all. Go wild.


Q.  What other sparse resources are available?

A.  Mailing list:  linux-sparse@vger.kernel.org
    (email majordomo@vger.kernel.org to subscribe)

    Git repository:  devel/sparse/sparse.git under http://kernel.org/git/
    BitKeeper repository:  bk://sparse.bkbits.net/sparse