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 56Getting sparse 57-------------- 58 59You can get tarballs of the latest released versions from: 60https://www.kernel.org/pub/software/devel/sparse/dist/ 61 62Alternatively, you can get snapshots of the latest development version 63of sparse using git to clone:: 64 65 git://git.kernel.org/pub/scm/devel/sparse/sparse.git 66 67Once you have it, just do:: 68 69 make 70 make install 71 72as a regular user, and it will install sparse in your ~/bin directory. 73 74Using sparse 75------------ 76 77Do a kernel make with "make C=1" to run sparse on all the C files that get 78recompiled, or use "make C=2" to run sparse on the files whether they need to 79be recompiled or not. The latter is a fast way to check the whole tree if you 80have already built it. 81 82The optional make variable CF can be used to pass arguments to sparse. The 83build system passes -Wbitwise to sparse automatically. 84 85Note that sparse defines the __CHECKER__ preprocessor symbol. 86