Root/Documentation/sparse.txt

1Copyright 2004 Linus Torvalds
2Copyright 2004 Pavel Machek <pavel@suse.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
57http://www.kernel.org/pub/linux/kernel/people/josh/sparse/
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/linux/kernel/git/josh/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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