105 lines
3.6 KiB
ReStructuredText
105 lines
3.6 KiB
ReStructuredText
.. Copyright 2004 Linus Torvalds
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.. Copyright 2004 Pavel Machek <pavel@ucw.cz>
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.. Copyright 2006 Bob Copeland <me@bobcopeland.com>
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Sparse
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======
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Sparse is a semantic checker for C programs; it can be used to find a
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number of potential problems with kernel code. See
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https://lwn.net/Articles/689907/ for an overview of sparse; this document
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contains some kernel-specific sparse information.
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More information on sparse, mainly about its internals, can be found in
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its official pages at https://sparse.docs.kernel.org.
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Using sparse for typechecking
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-----------------------------
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"__bitwise" is a type attribute, so you have to do something like this::
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typedef int __bitwise pm_request_t;
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enum pm_request {
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PM_SUSPEND = (__force pm_request_t) 1,
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PM_RESUME = (__force pm_request_t) 2
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};
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which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is
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there because sparse will complain about casting to/from a bitwise type,
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but in this case we really _do_ want to force the conversion). And because
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the enum values are all the same type, now "enum pm_request" will be that
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type too.
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And with gcc, all the "__bitwise"/"__force stuff" goes away, and it all
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ends up looking just like integers to gcc.
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Quite frankly, you don't need the enum there. The above all really just
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boils down to one special "int __bitwise" type.
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So the simpler way is to just do::
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typedef int __bitwise pm_request_t;
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#define PM_SUSPEND ((__force pm_request_t) 1)
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#define PM_RESUME ((__force pm_request_t) 2)
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and you now have all the infrastructure needed for strict typechecking.
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One small note: the constant integer "0" is special. You can use a
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constant zero as a bitwise integer type without sparse ever complaining.
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This is because "bitwise" (as the name implies) was designed for making
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sure that bitwise types don't get mixed up (little-endian vs big-endian
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vs cpu-endian vs whatever), and there the constant "0" really _is_
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special.
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Using sparse for lock checking
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------------------------------
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The following macros are undefined for gcc and defined during a sparse
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run to use the "context" tracking feature of sparse, applied to
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locking. These annotations tell sparse when a lock is held, with
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regard to the annotated function's entry and exit.
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__must_hold - The specified lock is held on function entry and exit.
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__acquires - The specified lock is held on function exit, but not entry.
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__releases - The specified lock is held on function entry, but not exit.
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If the function enters and exits without the lock held, acquiring and
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releasing the lock inside the function in a balanced way, no
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annotation is needed. The three annotations above are for cases where
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sparse would otherwise report a context imbalance.
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Getting sparse
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--------------
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You can get tarballs of the latest released versions from:
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https://www.kernel.org/pub/software/devel/sparse/dist/
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Alternatively, you can get snapshots of the latest development version
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of sparse using git to clone::
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git://git.kernel.org/pub/scm/devel/sparse/sparse.git
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Once you have it, just do::
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make
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make install
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as a regular user, and it will install sparse in your ~/bin directory.
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Using sparse
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------------
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Do a kernel make with "make C=1" to run sparse on all the C files that get
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recompiled, or use "make C=2" to run sparse on the files whether they need to
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be recompiled or not. The latter is a fast way to check the whole tree if you
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have already built it.
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The optional make variable CF can be used to pass arguments to sparse. The
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build system passes -Wbitwise to sparse automatically.
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Note that sparse defines the __CHECKER__ preprocessor symbol.
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