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authorMarcelo Schmitt <marcelo.schmitt1@gmail.com>2022-03-31 00:49:59 +0300
committerJonathan Corbet <corbet@lwn.net>2022-04-05 18:48:25 +0300
commita32d5c0fc12b1dec44ddd97434cbb0203c7e60e5 (patch)
tree181b60601905b14a42ad72b196961376be8e7825 /Documentation/dev-tools/testing-overview.rst
parent12379401c000495e683c5c5574b82a64f8d826d6 (diff)
downloadlinux-a32d5c0fc12b1dec44ddd97434cbb0203c7e60e5.tar.xz
Documentation: dev-tools: Enhance static analysis section with discussion
Enhance the static analysis tools section with a discussion on when to use each of them. This was mainly taken from Dan Carpenter and Julia Lawall's comments on a previous documentation patch for static analysis tools. Lore: https://lore.kernel.org/linux-doc/20220329090911.GX3293@kadam/T/#mb97770c8e938095aadc3ee08f4ac7fe32ae386e6 Signed-off-by: Marcelo Schmitt <marcelo.schmitt1@gmail.com> Acked-by: David Gow <davidgow@google.com> Cc: Dan Carpenter <dan.carpenter@oracle.com> Cc: Julia Lawall <julia.lawall@inria.fr> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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@@ -146,3 +146,35 @@ Documentation/dev-tools/coccinelle.rst documentation page for details.
Beware, though, that static analysis tools suffer from **false positives**.
Errors and warns need to be evaluated carefully before attempting to fix them.
+
+When to use Sparse and Smatch
+-----------------------------
+
+Sparse does type checking, such as verifying that annotated variables do not
+cause endianness bugs, detecting places that use ``__user`` pointers improperly,
+and analyzing the compatibility of symbol initializers.
+
+Smatch does flow analysis and, if allowed to build the function database, it
+also does cross function analysis. Smatch tries to answer questions like where
+is this buffer allocated? How big is it? Can this index be controlled by the
+user? Is this variable larger than that variable?
+
+It's generally easier to write checks in Smatch than it is to write checks in
+Sparse. Nevertheless, there are some overlaps between Sparse and Smatch checks.
+
+Strong points of Smatch and Coccinelle
+--------------------------------------
+
+Coccinelle is probably the easiest for writing checks. It works before the
+pre-processor so it's easier to check for bugs in macros using Coccinelle.
+Coccinelle also creates patches for you, which no other tool does.
+
+For example, with Coccinelle you can do a mass conversion from
+``kmalloc(x * size, GFP_KERNEL)`` to ``kmalloc_array(x, size, GFP_KERNEL)``, and
+that's really useful. If you just created a Smatch warning and try to push the
+work of converting on to the maintainers they would be annoyed. You'd have to
+argue about each warning if can really overflow or not.
+
+Coccinelle does no analysis of variable values, which is the strong point of
+Smatch. On the other hand, Coccinelle allows you to do simple things in a simple
+way.