linux-kernel - [PATCH v2 2/2] Documentation: dev-tools: Enhance static analysis section with discussion

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Message-ID: <11f4750c6d4c175994dfd36d1ff385f68f61bd02.1648593132.git.marcelo.schmitt1@gmail.com>
Date:   Tue, 29 Mar 2022 20:23:14 -0300
From:   Marcelo Schmitt <marcelo.schmitt1@...il.com>
To:     corbet@....net, mchehab+huawei@...nel.org, dlatypov@...gle.com,
        davidgow@...gle.com
Cc:     linux-doc@...r.kernel.org, linux-sparse@...r.kernel.org,
        cocci@...ia.fr, smatch@...r.kernel.org,
        linux-kernel@...r.kernel.org, skhan@...uxfoundation.org,
        dan.carpenter@...cle.com, julia.lawall@...ia.fr
Subject: [PATCH v2 2/2] 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
the 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@...il.com>
Cc: Dan Carpenter <dan.carpenter@...cle.com>
Cc: Julia Lawall <julia.lawall@...ia.fr>
---
 Documentation/dev-tools/testing-overview.rst | 33 ++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/Documentation/dev-tools/testing-overview.rst b/Documentation/dev-tools/testing-overview.rst
index b5e02dd3fd94..91e479045d3a 100644
--- a/Documentation/dev-tools/testing-overview.rst
+++ b/Documentation/dev-tools/testing-overview.rst
@@ -146,3 +146,36 @@ 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 is useful for type checking, detecting places that use ``__user``
+pointers improperly, or finding endianness bugs. Sparse runs much faster than
+Smatch.
+
+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
+because there is no reason for re-implementing Sparse's check in Smatch.
+
+Strong points of Smatch and Coccinelle
+--------------------------------------
+
+Coccinelle is probably the easiest for writing checks. It works before the
+pre-compiler so it's easier to check for bugs in macros using Coccinelle.
+Coccinelle also writes patches fixes for you which no other tool does.
+
+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