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
  52
  53Getting sparse
  54~~~~~~~~~~~~~~
  55
  56You can get latest released versions from the Sparse homepage at
  57https://sparse.wiki.kernel.org/index.php/Main_Page
  58
  59Alternatively, you can get snapshots of the latest development version
  60of sparse using git to clone..
  61
  62        git://git.kernel.org/pub/scm/devel/sparse/sparse.git
  63
  64DaveJ has hourly generated tarballs of the git tree available at..
  65
  66        http://www.codemonkey.org.uk/projects/git-snapshots/sparse/
  67
  68
  69Once you have it, just do
  70
  71        make
  72        make install
  73
  74as a regular user, and it will install sparse in your ~/bin directory.
  75
  76Using sparse
  77~~~~~~~~~~~~
  78
  79Do a kernel make with "make C=1" to run sparse on all the C files that get
  80recompiled, or use "make C=2" to run sparse on the files whether they need to
  81be recompiled or not.  The latter is a fast way to check the whole tree if you
  82have already built it.
  83
  84The optional make variable CF can be used to pass arguments to sparse.  The
  85build system passes -Wbitwise to sparse automatically.  To perform endianness
  86checks, you may define __CHECK_ENDIAN__:
  87
  88        make C=2 CF="-D__CHECK_ENDIAN__"
  89
  90These checks are disabled by default as they generate a host of warnings.
  91
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