Sparse

<h2 id="annotations">Annotations</h2>
<p>Some of the checks performed by Sparse require annotating the source code using the __attribute__ <a href="/facts/GNU_Compiler_Collection/t07jh01k">GCC</a> extension, or the Sparse-specific __context__ specifier.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> Sparse defines the following list of attributes:
</p>
<ul><li>address_space(<i>num</i>)</li>
<li>bitwise</li>
<li>force</li>
<li>context(<i>expression</i>,<i>in_context</i>,<i>out_context</i>)</li></ul>
<p>When an API is defined with a macro, the specifier __attribute__((context(<i>...</i>))) can be replaced by __context__(<i>...</i>).
</p>
<h3>Linux kernel definitions</h3>
<p>The Linux kernel defines the following short forms as pre-processor macros in files <a href="http://lxr.linux.no/linux+*/include/linux/compiler.h">linux/compiler.h</a> and <a href="http://lxr.linux.no/linux+*/include/linux/types.h">linux/types.h</a> (when building without the __CHECKER__ flag, all these annotations are removed from the code):
</p>
#ifdef __CHECKER__
# define __user		__attribute__((noderef, address_space(1)))
# define __kernel	__attribute__((address_space(0)))
# define __safe		__attribute__((safe))
# define __force	__attribute__((force))
# define __nocast	__attribute__((nocast))
# define __iomem	__attribute__((noderef, address_space(2)))
# define __must_hold(x)	__attribute__((context(x,1,1)))
# define __acquires(x)	__attribute__((context(x,0,1)))
# define __releases(x)	__attribute__((context(x,1,0)))
# define __acquire(x)	__context__(x,1)
# define __release(x)	__context__(x,-1)
# define __cond_lock(x,c)	((c) ? ({ __acquire(x); 1; }) : 0)
# define __percpu	__attribute__((noderef, address_space(3)))
#ifdef CONFIG_SPARSE_RCU_POINTER
# define __rcu		__attribute__((noderef, address_space(4)))
#else
# define __rcu
#endif
extern void __chk_user_ptr(const volatile void __user *);
extern void __chk_io_ptr(const volatile void __iomem *);
#else
# define __user
# define __kernel
# define __safe
# define __force
# define __nocast
# define __iomem
# define __chk_user_ptr(x) (void)0
# define __chk_io_ptr(x) (void)0
# define __builtin_warning(x, y...) (1)
# define __must_hold(x)
# define __acquires(x)
# define __releases(x)
# define __acquire(x) (void)0
# define __release(x) (void)0
# define __cond_lock(x,c) (c)
# define __percpu
# define __rcu
#endif

#ifdef __CHECKER__
# define __bitwise    __attribute__((bitwise))
#else
# define __bitwise
#endif

<h3>Examples</h3>
<p>The types __le32 and __be32 represent 32-bit integer types with different <a href="/facts/Endianness/wbrQnyu3">endianness</a>. However, the C language does not allow to specify that variables of these types should not be mixed. The bitwise attribute is used to mark these types as restricted, so Sparse will give a warning if variables of these types or other integer variables are mixed:
</p>
typedef __u32 __bitwise     __le32;
typedef __u32 __bitwise     __be32;

<p>To mark valid conversions between restricted types, a casting with the force attribute is used to avoid Sparse giving a warning.
</p>
<h2 id="see-also">See also</h2>
<ul>
<li>Free and open-source software portal</li></ul>
<ul><li><a href="/facts/List_of_tools_for_static_code_analysis/E9bcvnrD">List of tools for static code analysis</a></li></ul>

<h2 id="further-reading">Further reading</h2>
<ul><li>Neil Brown (2016-06-08). <a href="https://lwn.net/Articles/689907/">"Sparse: a look under the hood"</a>. <i><a href="/facts/LWN.net/8uTsltvM">LWN.net</a></i>. Retrieved 2021-11-26.</li>
<li>Jonathan Corbet (2004-06-01). <a href="https://lwn.net/Articles/87538/">"Finding kernel problems automatically"</a>. <i><a href="/facts/LWN.net/8uTsltvM">LWN.net</a></i>. Retrieved 2021-11-26.</li>
<li>Doc Searls (2003-11-24). <a href="http://www.linuxjournal.com/article/7272">"Linus & the Lunatics, Part I"</a>. <i><a href="/facts/Linux_Journal/m7rosgex">Linux Journal</a></i>. Retrieved 2021-11-26.</li>
<li>Subrata Modak; Balbir Singh; Yamato Masatake (2009). <a href="https://www.kernel.org/doc/ols/2009/ols2009-pages-209-220.pdf"><i>Putting LTP to test—Validating both the Linux kernel and Test-cases</i></a> (PDF). <a href="https://www.kernel.org/doc/ols/2009/">Ottawa Linux Symposium 2009</a>. pp. 209–220. Retrieved 2021-11-26.</li>
<li>Daniel De Graaf (2010). <a href="http://archives.ece.iastate.edu/archive/00000566/01/thesis.pdf"><i>Detection of Static Flaws in Changesets</i></a> (PDF) (M.Sc. thesis). Ames, Iowa: Iowa State University. <a href="/facts/OCLC_(identifier)/Yqad8waq">OCLC</a> <a href="https://search.worldcat.org/oclc/665146513">665146513</a>. Retrieved 2010-11-07.</li></ul>
<h2 id="external-links">External links</h2>
<ul><li><a href="https://sparse.docs.kernel.org">Official documentation</a></li>
<li><a href="https://www.kernel.org/doc/html/latest/dev-tools/sparse.html">Using sparse for typechecking</a>, <i>Linux Kernel Documentation</i></li>
<li><a href="https://manned.org/sparse.1">sparse(1)</a>: Semantic Parser for C – <a href="/facts/Linux/9FvCKSTq">Linux</a> User <a href="/facts/Man_page/S2yYjy0J">Manual</a> – User Commands</li>
<li><a href="https://manned.org/cgcc.1">cgcc(1)</a>: Compiler wrapper to run Sparse after compiling – <a href="/facts/Linux/9FvCKSTq">Linux</a> User <a href="/facts/Man_page/S2yYjy0J">Manual</a> – User Commands</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Yoann Padioleau; René Rydhof Hansen; Julia L. Lawall; Gilles Muller (2006). Semantic patches for documenting and automating collateral evolutions in Linux device drivers. Proceedings of the 3rd workshop on Programming languages and operating systems: linguistic support for modern operating systems. CiteSeerX 10.1.1.122.7080. doi:10.1145/1215995.1216005. ISBN 1-59593-577-0. The Linux community has recently begun using various tools to better analyze C code. Sparse is a library that, like a compiler front end, provides convenient access to the abstract syntax tree and typing information of a C program. <a href="1-59593-577-0" target="_blank">1-59593-577-0</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Christopher Li (2009-10-16). "Sparse 0.4.2 released". linux-sparse (Mailing list). Retrieved 2010-11-06. <a href="https://marc.info/?l=linux-sparse&m=125570805231414&w=2" target="_blank">https://marc.info/?l=linux-sparse&m=125570805231414&w=2</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>change Sparse's maintainer, retrieved December 10, 2018 <a href="https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/MAINTAINERS?id=4e962ff6e34f44c400c548da0c1e2393053a691e" target="_blank">https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/MAINTAINERS?id=4e962ff6e34f44c400c548da0c1e2393053a691e</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>"Attribute Syntax — Using the GNU Compiler Collection (GCC)". Free Software Foundation. Retrieved 2010-11-13. <a href="https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html" target="_blank">https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
</ol>

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Sparse