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Date:   Wed, 30 Mar 2022 18:49:59 -0300
From:   Marcelo Schmitt <marcelo.schmitt1@gmail.com>
To:     corbet@lwn.net, mchehab+huawei@kernel.org, dlatypov@google.com,
        davidgow@google.com
Cc:     linux-doc@vger.kernel.org, linux-sparse@vger.kernel.org,
        cocci@inria.fr, smatch@vger.kernel.org,
        linux-kernel@vger.kernel.org, skhan@linuxfoundation.org,
        dan.carpenter@oracle.com, julia.lawall@inria.fr
Subject: [PATCH v3 2/2] Documentation: dev-tools: Enhance static analysis
 section with discussion
Message-ID: <62f461a20600b95e694016c4e5348ef2e260fa87.1648674305.git.marcelo.schmitt1@gmail.com>
References: <cover.1648674305.git.marcelo.schmitt1@gmail.com>
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Precedence: bulk

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>
---
Change log v2 -> v3:
- Changed the paragraph about Sparse to make it sound better (hopefully)
- Minor adjusts to make the considerations about Coccinelle sound better
  and be precise

 Documentation/dev-tools/testing-overview.rst | 32 ++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/Documentation/dev-tools/testing-overview.rst b/Documentation/dev-tools/testing-overview.rst
index b5e02dd3fd94..0aaf6ea53608 100644
--- a/Documentation/dev-tools/testing-overview.rst
+++ b/Documentation/dev-tools/testing-overview.rst
@@ -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.
-- 
2.35.1