linux/Documentation/sparse.txt
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   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.
 109
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