[linux.git] / Documentation / sparse.txt

Copyright 2004 Linus Torvalds
Copyright 2004 Pavel Machek <[email protected]>
Copyright 2006 Bob Copeland <[email protected]>

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.

Getting 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 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 get
recompiled, or use "make C=2" to run sparse on the files whether they need to
be recompiled or not.  The latter is a fast way to check the whole tree if you
have already built it.

The optional make variable CHECKFLAGS can be used to pass arguments to sparse.
The build system passes -Wbitwise to sparse automatically.  To perform
endianness checks, you may define __CHECK_ENDIAN__:

        make C=2 CHECKFLAGS="-D__CHECK_ENDIAN__"

These checks are disabled by default as they generate a host of warnings.
Commit	Line	Data
1da177e4 LT	1	Copyright 2004 Linus Torvalds
1da177e4 LT	2	Copyright 2004 Pavel Machek <[email protected]>
e8331951	3	Copyright 2006 Bob Copeland <[email protected]>
1da177e4 LT	4
	5	Using sparse for typechecking
	6	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	7
	8	"__bitwise" is a type attribute, so you have to do something like this:
	9
	10	typedef int __bitwise pm_request_t;
	11
	12	enum pm_request {
	13	PM_SUSPEND = (__force pm_request_t) 1,
	14	PM_RESUME = (__force pm_request_t) 2
	15	};
	16
	17	which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is
	18	there because sparse will complain about casting to/from a bitwise type,
	19	but in this case we really _do_ want to force the conversion). And because
	20	the enum values are all the same type, now "enum pm_request" will be that
	21	type too.
	22
	23	And with gcc, all the __bitwise/__force stuff goes away, and it all ends
	24	up looking just like integers to gcc.
	25
	26	Quite frankly, you don't need the enum there. The above all really just
	27	boils down to one special "int __bitwise" type.
	28
	29	So the simpler way is to just do
	30
	31	typedef int __bitwise pm_request_t;
	32
	33	#define PM_SUSPEND ((__force pm_request_t) 1)
	34	#define PM_RESUME ((__force pm_request_t) 2)
	35
	36	and you now have all the infrastructure needed for strict typechecking.
	37
	38	One small note: the constant integer "0" is special. You can use a
	39	constant zero as a bitwise integer type without sparse ever complaining.
	40	This is because "bitwise" (as the name implies) was designed for making
	41	sure that bitwise types don't get mixed up (little-endian vs big-endian
	42	vs cpu-endian vs whatever), and there the constant "0" really _is_
	43	special.
	44
e8331951 BC	45	Getting sparse
e8331951 BC	46	~~~~~~~~~~~~~~
1da177e4	47
86513e72	48	With git, you can just get it from
1da177e4	49
86513e72	50	rsync://rsync.kernel.org/pub/scm/devel/sparse/sparse.git
1da177e4 LT	51
	52	and DaveJ has tar-balls at
	53
e8331951	54	http://www.codemonkey.org.uk/projects/git-snapshots/sparse/
1da177e4 LT	55
	56
	57	Once you have it, just do
	58
	59	make
	60	make install
	61
e8331951 BC	62	as a regular user, and it will install sparse in your ~/bin directory.
	63
	64	Using sparse
	65	~~~~~~~~~~~~
	66
	67	Do a kernel make with "make C=1" to run sparse on all the C files that get
	68	recompiled, or use "make C=2" to run sparse on the files whether they need to
	69	be recompiled or not. The latter is a fast way to check the whole tree if you
	70	have already built it.
	71
1c7bafe7 RD	72	The optional make variable CHECKFLAGS can be used to pass arguments to sparse.
	73	The build system passes -Wbitwise to sparse automatically. To perform
	74	endianness checks, you may define __CHECK_ENDIAN__:
e8331951	75
1c7bafe7	76	make C=2 CHECKFLAGS="-D__CHECK_ENDIAN__"
e8331951 BC	77
e8331951 BC	78	These checks are disabled by default as they generate a host of warnings.