linux/Documentation/sparse.txt

Copyright 2004 Linus Torvalds
Copyright 2004 Pavel Machek <pavel@suse.cz>

Using sparse for typechecking
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

"__bitwise" is a type attribute, so you have to do something like this:

        typedef int __bitwise pm_request_t;

        enum pm_request {
                PM_SUSPEND = (__force pm_request_t) 1,
                PM_RESUME = (__force pm_request_t) 2
        };

which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is
there because sparse will complain about casting to/from a bitwise type,
but in this case we really _do_ want to force the conversion). And because
the enum values are all the same type, now "enum pm_request" will be that
type too.

And with gcc, all the __bitwise/__force stuff goes away, and it all ends
up looking just like integers to gcc.

Quite frankly, you don't need the enum there. The above all really just
boils down to one special "int __bitwise" type.

So the simpler way is to just do

        typedef int __bitwise pm_request_t;

        #define PM_SUSPEND ((__force pm_request_t) 1)
        #define PM_RESUME ((__force pm_request_t) 2)

and you now have all the infrastructure needed for strict typechecking.

One small note: the constant integer "0" is special. You can use a
constant zero as a bitwise integer type without sparse ever complaining.
This is because "bitwise" (as the name implies) was designed for making
sure that bitwise types don't get mixed up (little-endian vs big-endian
vs cpu-endian vs whatever), and there the constant "0" really _is_
special.

Modify top-level Makefile to say

CHECK           = sparse -Wbitwise

or you don't get any checking at all.


Where to get sparse
~~~~~~~~~~~~~~~~~~~

With git, you can just get it from

        rsync://rsync.kernel.org/pub/scm/devel/sparse/sparse.git

and DaveJ has tar-balls at

	http://www.codemonkey.org.uk/projects/git-snapshots/sparse/


Once you have it, just do

        make
        make install

as your regular user, and it will install sparse in your ~/bin directory.
After that, doing a kernel make with "make C=1" will run sparse on all the
C files that get recompiled, or with "make C=2" will run sparse on the
files whether they need to be recompiled or not (ie the latter is fast way
to check the whole tree if you have already built it).