mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-26 10:49:33 +00:00
![Bjorn Helgaas](/assets/img/avatar_default.png)
Several attributes depend on __CHECKER__, but previously there was no clue in the tree about when __CHECKER__ might be defined. Add hints at the most common places (__kernel, __user, __iomem, __bitwise) and in the sparse documentation. Link: https://lkml.kernel.org/r/20220310220927.245704-3-helgaas@kernel.org Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Nathan Chancellor <nathan@kernel.org> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: "Michael S . Tsirkin" <mst@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
104 lines
3.6 KiB
ReStructuredText
104 lines
3.6 KiB
ReStructuredText
.. Copyright 2004 Linus Torvalds
|
|
.. Copyright 2004 Pavel Machek <pavel@ucw.cz>
|
|
.. Copyright 2006 Bob Copeland <me@bobcopeland.com>
|
|
|
|
Sparse
|
|
======
|
|
|
|
Sparse is a semantic checker for C programs; it can be used to find a
|
|
number of potential problems with kernel code. See
|
|
https://lwn.net/Articles/689907/ for an overview of sparse; this document
|
|
contains some kernel-specific sparse information.
|
|
More information on sparse, mainly about its internals, can be found in
|
|
its official pages at https://sparse.docs.kernel.org.
|
|
|
|
|
|
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.
|
|
|
|
Using sparse for lock checking
|
|
------------------------------
|
|
|
|
The following macros are undefined for gcc and defined during a sparse
|
|
run to use the "context" tracking feature of sparse, applied to
|
|
locking. These annotations tell sparse when a lock is held, with
|
|
regard to the annotated function's entry and exit.
|
|
|
|
__must_hold - The specified lock is held on function entry and exit.
|
|
|
|
__acquires - The specified lock is held on function exit, but not entry.
|
|
|
|
__releases - The specified lock is held on function entry, but not exit.
|
|
|
|
If the function enters and exits without the lock held, acquiring and
|
|
releasing the lock inside the function in a balanced way, no
|
|
annotation is needed. The three annotations above are for cases where
|
|
sparse would otherwise report a context imbalance.
|
|
|
|
Getting sparse
|
|
--------------
|
|
|
|
You can get tarballs of the latest released versions from:
|
|
https://www.kernel.org/pub/software/devel/sparse/dist/
|
|
|
|
Alternatively, you can get snapshots of the latest development version
|
|
of sparse using git to clone::
|
|
|
|
git://git.kernel.org/pub/scm/devel/sparse/sparse.git
|
|
|
|
Once you have it, just do::
|
|
|
|
make
|
|
make install
|
|
|
|
as a regular user, and it will install sparse in your ~/bin directory.
|
|
|
|
Using sparse
|
|
------------
|
|
|
|
Do a kernel make with "make C=1" to run sparse on all the C files that get
|
|
recompiled, or use "make C=2" to run sparse on the files whether they need to
|
|
be recompiled or not. The latter is a fast way to check the whole tree if you
|
|
have already built it.
|
|
|
|
The optional make variable CF can be used to pass arguments to sparse. The
|
|
build system passes -Wbitwise to sparse automatically.
|
|
|
|
Note that sparse defines the __CHECKER__ preprocessor symbol.
|