1Copyright 2004 Linus Torvalds
  2Copyright 2004 Pavel Machek <pavel@ucw.cz>
  3Copyright 2006 Bob Copeland <me@bobcopeland.com>
  4
  5Using 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
 17which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is
 18there because sparse will complain about casting to/from a bitwise type,
 19but in this case we really _do_ want to force the conversion). And because
 20the enum values are all the same type, now "enum pm_request" will be that
 21type too.
 22
 23And with gcc, all the __bitwise/__force stuff goes away, and it all ends
 24up looking just like integers to gcc.
 25
 26Quite frankly, you don't need the enum there. The above all really just
 27boils down to one special "int __bitwise" type.
 28
 29So 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
 36and you now have all the infrastructure needed for strict typechecking.
 37
 38One small note: the constant integer "0" is special. You can use a
 39constant zero as a bitwise integer type without sparse ever complaining.
 40This is because "bitwise" (as the name implies) was designed for making
 41sure that bitwise types don't get mixed up (little-endian vs big-endian
 42vs cpu-endian vs whatever), and there the constant "0" really _is_
 43special.
 44
 45__bitwise__ - to be used for relatively compact stuff (gfp_t, etc.) that
 46is mostly warning-free and is supposed to stay that way.  Warnings will
 47be generated without __CHECK_ENDIAN__.
 48
 49__bitwise - noisy stuff; in particular, __le*/__be* are that.  We really
 50don't want to drown in noise unless we'd explicitly asked for it.
 51
 52Using sparse for lock checking
 53~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 54
 55The following macros are undefined for gcc and defined during a sparse
 56run to use the "context" tracking feature of sparse, applied to
 57locking.  These annotations tell sparse when a lock is held, with
 58regard to the annotated function's entry and exit.
 59
 60__must_hold - The specified lock is held on function entry and exit.
 61
 62__acquires - The specified lock is held on function exit, but not entry.
 63
 64__releases - The specified lock is held on function entry, but not exit.
 65
 66If the function enters and exits without the lock held, acquiring and
 67releasing the lock inside the function in a balanced way, no
 68annotation is needed.  The tree annotations above are for cases where
 69sparse would otherwise report a context imbalance.
 70
 71Getting sparse
 72~~~~~~~~~~~~~~
 73
 74You can get latest released versions from the Sparse homepage at
 75https://sparse.wiki.kernel.org/index.php/Main_Page
 76
 77Alternatively, you can get snapshots of the latest development version
 78of sparse using git to clone..
 79
 80        git://git.kernel.org/pub/scm/devel/sparse/sparse.git
 81
 82DaveJ has hourly generated tarballs of the git tree available at..
 83
 84        http://www.codemonkey.org.uk/projects/git-snapshots/sparse/
 85
 86
 87Once you have it, just do
 88
 89        make
 90        make install
 91
 92as a regular user, and it will install sparse in your ~/bin directory.
 93
 94Using sparse
 95~~~~~~~~~~~~
 96
 97Do a kernel make with "make C=1" to run sparse on all the C files that get
 98recompiled, or use "make C=2" to run sparse on the files whether they need to
 99be recompiled or not.  The latter is a fast way to check the whole tree if you
100have already built it.
101
102The optional make variable CF can be used to pass arguments to sparse.  The
103build system passes -Wbitwise to sparse automatically.  To perform endianness
104checks, you may define __CHECK_ENDIAN__:
105
106        make C=2 CF="-D__CHECK_ENDIAN__"
107
108These checks are disabled by default as they generate a host of warnings.