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1.. Copyright 2004 Linus Torvalds2.. Copyright 2004 Pavel Machek <pavel@ucw.cz>3.. Copyright 2006 Bob Copeland <me@bobcopeland.com>4 5Sparse6======7 8Sparse is a semantic checker for C programs; it can be used to find a9number of potential problems with kernel code. See10https://lwn.net/Articles/689907/ for an overview of sparse; this document11contains some kernel-specific sparse information.12More information on sparse, mainly about its internals, can be found in13its official pages at https://sparse.docs.kernel.org.14 15 16Using sparse for typechecking17-----------------------------18 19"__bitwise" is a type attribute, so you have to do something like this::20 21 typedef int __bitwise pm_request_t;22 23 enum pm_request {24 PM_SUSPEND = (__force pm_request_t) 1,25 PM_RESUME = (__force pm_request_t) 226 };27 28which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is29there because sparse will complain about casting to/from a bitwise type,30but in this case we really _do_ want to force the conversion). And because31the enum values are all the same type, now "enum pm_request" will be that32type too.33 34And with gcc, all the "__bitwise"/"__force stuff" goes away, and it all35ends up looking just like integers to gcc.36 37Quite frankly, you don't need the enum there. The above all really just38boils down to one special "int __bitwise" type.39 40So the simpler way is to just do::41 42 typedef int __bitwise pm_request_t;43 44 #define PM_SUSPEND ((__force pm_request_t) 1)45 #define PM_RESUME ((__force pm_request_t) 2)46 47and you now have all the infrastructure needed for strict typechecking.48 49One small note: the constant integer "0" is special. You can use a50constant zero as a bitwise integer type without sparse ever complaining.51This is because "bitwise" (as the name implies) was designed for making52sure that bitwise types don't get mixed up (little-endian vs big-endian53vs cpu-endian vs whatever), and there the constant "0" really _is_54special.55 56Using sparse for lock checking57------------------------------58 59The following macros are undefined for gcc and defined during a sparse60run to use the "context" tracking feature of sparse, applied to61locking. These annotations tell sparse when a lock is held, with62regard to the annotated function's entry and exit.63 64__must_hold - The specified lock is held on function entry and exit.65 66__acquires - The specified lock is held on function exit, but not entry.67 68__releases - The specified lock is held on function entry, but not exit.69 70If the function enters and exits without the lock held, acquiring and71releasing the lock inside the function in a balanced way, no72annotation is needed. The three annotations above are for cases where73sparse would otherwise report a context imbalance.74 75Getting sparse76--------------77 78You can get tarballs of the latest released versions from:79https://www.kernel.org/pub/software/devel/sparse/dist/80 81Alternatively, you can get snapshots of the latest development version82of sparse using git to clone::83 84 git://git.kernel.org/pub/scm/devel/sparse/sparse.git85 86Once you have it, just do::87 88 make89 make install90 91as a regular user, and it will install sparse in your ~/bin directory.92 93Using sparse94------------95 96Do a kernel make with "make C=1" to run sparse on all the C files that get97recompiled, or use "make C=2" to run sparse on the files whether they need to98be recompiled or not. The latter is a fast way to check the whole tree if you99have already built it.100 101The optional make variable CF can be used to pass arguments to sparse. The102build system passes -Wbitwise to sparse automatically.103 104Note that sparse defines the __CHECKER__ preprocessor symbol.105