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. 12 13 14Using sparse for typechecking 15----------------------------- 16 17"__bitwise" is a type attribute, so you have to do something like this:: 18 19 typedef int __bitwise pm_request_t; 20 21 enum pm_request { 22 PM_SUSPEND = (__force pm_request_t) 1, 23 PM_RESUME = (__force pm_request_t) 2 24 }; 25 26which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is 27there because sparse will complain about casting to/from a bitwise type, 28but in this case we really _do_ want to force the conversion). And because 29the enum values are all the same type, now "enum pm_request" will be that 30type too. 31 32And with gcc, all the "__bitwise"/"__force stuff" goes away, and it all 33ends up looking just like integers to gcc. 34 35Quite frankly, you don't need the enum there. The above all really just 36boils down to one special "int __bitwise" type. 37 38So the simpler way is to just do:: 39 40 typedef int __bitwise pm_request_t; 41 42 #define PM_SUSPEND ((__force pm_request_t) 1) 43 #define PM_RESUME ((__force pm_request_t) 2) 44 45and you now have all the infrastructure needed for strict typechecking. 46 47One small note: the constant integer "0" is special. You can use a 48constant zero as a bitwise integer type without sparse ever complaining. 49This is because "bitwise" (as the name implies) was designed for making 50sure that bitwise types don't get mixed up (little-endian vs big-endian 51vs cpu-endian vs whatever), and there the constant "0" really _is_ 52special. 53 54__bitwise__ - to be used for relatively compact stuff (gfp_t, etc.) that 55is mostly warning-free and is supposed to stay that way. Warnings will 56be generated without __CHECK_ENDIAN__. 57 58__bitwise - noisy stuff; in particular, __le*/__be* are that. We really 59don't want to drown in noise unless we'd explicitly asked for it. 60 61Using sparse for lock checking 62------------------------------ 63 64The following macros are undefined for gcc and defined during a sparse 65run to use the "context" tracking feature of sparse, applied to 66locking. These annotations tell sparse when a lock is held, with 67regard to the annotated function's entry and exit. 68 69__must_hold - The specified lock is held on function entry and exit. 70 71__acquires - The specified lock is held on function exit, but not entry. 72 73__releases - The specified lock is held on function entry, but not exit. 74 75If the function enters and exits without the lock held, acquiring and 76releasing the lock inside the function in a balanced way, no 77annotation is needed. The tree annotations above are for cases where 78sparse would otherwise report a context imbalance. 79 80Getting sparse 81-------------- 82 83You can get latest released versions from the Sparse homepage at 84https://sparse.wiki.kernel.org/index.php/Main_Page 85 86Alternatively, you can get snapshots of the latest development version 87of sparse using git to clone:: 88 89 git://git.kernel.org/pub/scm/devel/sparse/sparse.git 90 91DaveJ has hourly generated tarballs of the git tree available at:: 92 93 http://www.codemonkey.org.uk/projects/git-snapshots/sparse/ 94 95 96Once you have it, just do:: 97 98 make 99 make install 100 101as a regular user, and it will install sparse in your ~/bin directory. 102 103Using sparse 104------------ 105 106Do a kernel make with "make C=1" to run sparse on all the C files that get 107recompiled, or use "make C=2" to run sparse on the files whether they need to 108be recompiled or not. The latter is a fast way to check the whole tree if you 109have already built it. 110 111The optional make variable CF can be used to pass arguments to sparse. The 112build system passes -Wbitwise to sparse automatically. To perform endianness 113checks, you may define __CHECK_ENDIAN__:: 114 115 make C=2 CF="-D__CHECK_ENDIAN__" 116 117These checks are disabled by default as they generate a host of warnings. 118