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” isthere because sparse will complain about casting to/from a bitwise type,but in this case we really _do_ want to force the conversion). And becausethe enum values are all the same type, now “enum pm_request” will be thattype too.

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

Quite frankly, you don’t need the enum there. The above all really justboils 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 aconstant zero as a bitwise integer type without sparse ever complaining.This is because “bitwise” (as the name implies) was designed for makingsure that bitwise types don’t get mixed up (little-endian vs big-endianvs cpu-endian vs whatever), and there the constant “0” really _is_special.

Using sparse for lock checking¶

The following macros are undefined for gcc and defined during a sparserun to use the “context” tracking feature of sparse, applied tolocking. These annotations tell sparse when a lock is held, withregard to the annotated function’s entry and exit.

__must_hold - The specified lock is held on function entry and exit.

__acquires - The specified lock is held on function exit, but not entry.

__releases - The specified lock is held on function entry, but not exit.

If the function enters and exits without the lock held, acquiring andreleasing the lock inside the function in a balanced way, noannotation is needed. The three annotations above are for cases wheresparse would otherwise report a context imbalance.

Getting sparse¶

You can get latest released versions from the Sparse homepage athttps://sparse.wiki.kernel.org/index.php/Main_Page

Alternatively, you can get snapshots of the latest development versionof sparse using git to clone:

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

Once you have it, just do:

makemake install

as a regular user, and it will install sparse in your ~/bin directory.

Using sparse¶

Do a kernel make with “make C=1” to run sparse on all the C files that getrecompiled, or use “make C=2” to run sparse on the files whether they need tobe recompiled or not. The latter is a fast way to check the whole tree if youhave already built it.

The optional make variable CF can be used to pass arguments to sparse. Thebuild system passes -Wbitwise to sparse automatically.