1.. Copyright 2004 Linus Torvalds 2.. Copyright 2004 Pavel Machek <pavel@ucw.cz> 3.. Copyright 2006 Bob Copeland <me@bobcopeland.com> 4 5Sparse 6====== 7 8Sparse is a semantic checker for C programs; it can be used to find a 9number of potential problems with kernel code. See 10https://lwn.net/Articles/689907/ for an overview of sparse; this document 11contains some kernel-specific sparse information. 12More information on sparse, mainly about its internals, can be found in 13its official pages at https://sparse.docs.kernel.org. 14 15 16Using sparse for typechecking 17----------------------------- 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) 2 26 }; 27 28which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is 29there because sparse will complain about casting to/from a bitwise type, 30but in this case we really _do_ want to force the conversion). And because 31the enum values are all the same type, now "enum pm_request" will be that 32type too. 33 34And with gcc, all the "__bitwise"/"__force stuff" goes away, and it all 35ends up looking just like integers to gcc. 36 37Quite frankly, you don't need the enum there. The above all really just 38boils 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 a 50constant zero as a bitwise integer type without sparse ever complaining. 51This is because "bitwise" (as the name implies) was designed for making 52sure that bitwise types don't get mixed up (little-endian vs big-endian 53vs cpu-endian vs whatever), and there the constant "0" really _is_ 54special. 55 56Using sparse for lock checking 57------------------------------ 58 59The following macros are undefined for gcc and defined during a sparse 60run to use the "context" tracking feature of sparse, applied to 61locking. These annotations tell sparse when a lock is held, with 62regard 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 and 71releasing the lock inside the function in a balanced way, no 72annotation is needed. The three annotations above are for cases where 73sparse would otherwise report a context imbalance. 74 75Getting sparse 76-------------- 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 version 82of sparse using git to clone:: 83 84 git://git.kernel.org/pub/scm/devel/sparse/sparse.git 85 86Once you have it, just do:: 87 88 make 89 make install 90 91as a regular user, and it will install sparse in your ~/bin directory. 92 93Using sparse 94------------ 95 96Do a kernel make with "make C=1" to run sparse on all the C files that get 97recompiled, or use "make C=2" to run sparse on the files whether they need to 98be recompiled or not. The latter is a fast way to check the whole tree if you 99have already built it. 100 101The optional make variable CF can be used to pass arguments to sparse. The 102build system passes -Wbitwise to sparse automatically. 103 104Note that sparse defines the __CHECKER__ preprocessor symbol. 105