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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 22:20:36 (GMT)
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 22:20:36 (GMT)
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/sparse.txt
Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+Copyright 2004 Linus Torvalds
+Copyright 2004 Pavel Machek <pavel@suse.cz>
+
+Using sparse for typechecking
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+"__bitwise" is a type attribute, so you have to do something like this:
+
+ typedef int __bitwise pm_request_t;
+
+ enum pm_request {
+ PM_SUSPEND = (__force pm_request_t) 1,
+ PM_RESUME = (__force pm_request_t) 2
+ };
+
+which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is
+there because sparse will complain about casting to/from a bitwise type,
+but in this case we really _do_ want to force the conversion). And because
+the enum values are all the same type, now "enum pm_request" will be that
+type too.
+
+And with gcc, all the __bitwise/__force stuff goes away, and it all ends
+up looking just like integers to gcc.
+
+Quite frankly, you don't need the enum there. The above all really just
+boils down to one special "int __bitwise" type.
+
+So the simpler way is to just do
+
+ typedef int __bitwise pm_request_t;
+
+ #define PM_SUSPEND ((__force pm_request_t) 1)
+ #define PM_RESUME ((__force pm_request_t) 2)
+
+and you now have all the infrastructure needed for strict typechecking.
+
+One small note: the constant integer "0" is special. You can use a
+constant zero as a bitwise integer type without sparse ever complaining.
+This is because "bitwise" (as the name implies) was designed for making
+sure that bitwise types don't get mixed up (little-endian vs big-endian
+vs cpu-endian vs whatever), and there the constant "0" really _is_
+special.
+
+Modify top-level Makefile to say
+
+CHECK = sparse -Wbitwise
+
+or you don't get any checking at all.
+
+
+Where to get sparse
+~~~~~~~~~~~~~~~~~~~
+
+With BK, you can just get it from
+
+ bk://sparse.bkbits.net/sparse
+
+and DaveJ has tar-balls at
+
+ http://www.codemonkey.org.uk/projects/bitkeeper/sparse/
+
+
+Once you have it, just do
+
+ make
+ make install
+
+as your regular user, and it will install sparse in your ~/bin directory.
+After that, doing a kernel make with "make C=1" will run sparse on all the
+C files that get recompiled, or with "make C=2" will run sparse on the
+files whether they need to be recompiled or not (ie the latter is fast way
+to check the whole tree if you have already built it).

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