Cppcheck Design: updated article
This commit is contained in:
Daniel Marjamäki
parent
7c58604f93
commit
2aad9de2e1
|
|
@ -5,6 +5,12 @@ xsltproc -o manual.html /usr/share/xml/docbook/stylesheet/nwalsh/xhtml/docbook.x
|
|||
xsltproc -o intermediate-fo-file.fo /usr/share/xml/docbook/stylesheet/nwalsh/fo/docbook.xsl manual.docbook
|
||||
fop -pdf manual.pdf -fo intermediate-fo-file.fo
|
||||
|
||||
xsltproc --stringparam generate.toc "article nop" -o intermediate-fo-file.fo /usr/share/xml/docbook/stylesheet/nwalsh/fo/docbook.xsl writing-rules.docbook
|
||||
fop -pdf writing-rules.pdf -fo intermediate-fo-file.fo
|
||||
xsltproc --stringparam generate.toc "article nop" -o intermediate-fo-file.fo /usr/share/xml/docbook/stylesheet/nwalsh/fo/docbook.xsl writing-rules-1.docbook
|
||||
fop -pdf writing-rules-1.pdf -fo intermediate-fo-file.fo
|
||||
|
||||
xsltproc --stringparam generate.toc "article nop" -o intermediate-fo-file.fo /usr/share/xml/docbook/stylesheet/nwalsh/fo/docbook.xsl writing-rules-2.docbook
|
||||
fop -pdf writing-rules-2.pdf -fo intermediate-fo-file.fo
|
||||
|
||||
xsltproc --stringparam generate.toc "article nop" -o intermediate-fo-file.fo /usr/share/xml/docbook/stylesheet/nwalsh/fo/docbook.xsl cppcheck-design.docbook
|
||||
fop -pdf cppcheck-design.pdf -fo intermediate-fo-file.fo
|
||||
|
||||
|
|
|
|||
|
|
@ -7,7 +7,7 @@
|
|||
xmlns:html="http://www.w3.org/1999/xhtml"
|
||||
xmlns:db="http://docbook.org/ns/docbook">
|
||||
<info>
|
||||
<title>Cppcheck Design Overview</title>
|
||||
<title>Cppcheck Design</title>
|
||||
|
||||
<author>
|
||||
<personname><firstname>Daniel</firstname><surname>Marjamäki</surname></personname>
|
||||
|
|
@ -23,63 +23,49 @@
|
|||
<section>
|
||||
<title>Introduction</title>
|
||||
|
||||
<para>This article is an overview of the design of Cppcheck.</para>
|
||||
<para>This article contains an overview of how Cppcheck works.</para>
|
||||
|
||||
<para>The design of Cppcheck are based on:</para>
|
||||
<para>The primary goal is that Cppcheck won't write any false warnings.
|
||||
This means that when an error is reported there must definitely be a bug
|
||||
in the code.</para>
|
||||
|
||||
<itemizedlist>
|
||||
<listitem>
|
||||
<para>Cppcheck will never be perfectly clever</para>
|
||||
</listitem>
|
||||
|
||||
<listitem>
|
||||
<para>No false warnings are allowed</para>
|
||||
</listitem>
|
||||
</itemizedlist>
|
||||
<para>The secondary goal is to detect as many bugs as possible.</para>
|
||||
</section>
|
||||
|
||||
<section>
|
||||
<title>Limitations of static analysis</title>
|
||||
|
||||
<para>It is not very reasonable to think that a static analysis tool will
|
||||
detect all bugs in your code.</para>
|
||||
<para>There are many bugs in programs that are really hard to detect for
|
||||
tools. Here is an example:</para>
|
||||
|
||||
<para>There are many bugs in programs that is really hard to detect for
|
||||
tools.</para>
|
||||
|
||||
<para>Many bugs are caused by wrong calculations. Here is an
|
||||
example:</para>
|
||||
|
||||
<programlisting>// calculate number of days
|
||||
<programlisting>// calculate the number of days
|
||||
int days(int hours)
|
||||
{
|
||||
return hours / 23;
|
||||
}</programlisting>
|
||||
|
||||
<para>A human programmer can see the error in that code because he knows
|
||||
<para>A human programmer knows that there are 24 hours in a day and
|
||||
therefore he could see that "23" is wrong. A tool will probably not know
|
||||
that there are 24 hours in a day.</para>
|
||||
|
||||
<para>Tools will probably not know that there are 24 hours in a
|
||||
day.</para>
|
||||
|
||||
<para>A tool that tries to guarantee that all bugs are found could write a
|
||||
warning message for every calculation in the program. In my humble opinion
|
||||
it wouldn't be usable to do that.</para>
|
||||
warning message for every "suspicious" calculation in the program. It
|
||||
might correctly report that "hours / 23" is wrong but incorrectly warn
|
||||
about "hours / 24".</para>
|
||||
|
||||
<para>Cppcheck will only write a warning message if it can determine that
|
||||
the calculation is wrong. This approach means that many bugs will not be
|
||||
detected.</para>
|
||||
the calculation is wrong. In this case, no error will be written.</para>
|
||||
</section>
|
||||
|
||||
<section>
|
||||
<title>Buffer overflows</title>
|
||||
|
||||
<para>This is a simple description of the buffer overflows checking in
|
||||
<para>This is a simple description of how buffer overflows are detected by
|
||||
Cppcheck.</para>
|
||||
|
||||
<para>For simple cases, no sophisticated control flow analysis is used. If
|
||||
an array is accessed out of bounds somewhere in its scope then an error
|
||||
message will be written.</para>
|
||||
<para>For simple cases, no control flow analysis is used. If an array is
|
||||
accessed out of bounds somewhere in its scope then an error message will
|
||||
be written.</para>
|
||||
|
||||
<para>An example code:</para>
|
||||
|
||||
|
|
@ -102,8 +88,8 @@ int days(int hours)
|
|||
statement is there and it has the error.</para>
|
||||
|
||||
<para>Cppcheck will also investigate function calls. But then control flow
|
||||
is needed to avoid false warnings. Here is an example that logically is
|
||||
the same as the previous example:</para>
|
||||
analysis is needed to avoid false warnings. Here is an example that
|
||||
logically is the same as the previous example:</para>
|
||||
|
||||
<para><programlisting>void f1(char *s)
|
||||
{
|
||||
|
|
@ -139,7 +125,7 @@ void f2()
|
|||
void f2()
|
||||
{
|
||||
char a[10];
|
||||
f1();
|
||||
f1(a);
|
||||
}</programlisting></para>
|
||||
</section>
|
||||
|
||||
|
|
@ -147,9 +133,8 @@ void f2()
|
|||
<title>Memory leaks</title>
|
||||
|
||||
<para>Simple control-flow analysis is made. The assumtion is that all
|
||||
conditions can always be either true or false.</para>
|
||||
|
||||
<para>It is assumed that all statements are reachable.</para>
|
||||
conditions can always be either true or false. It is assumed that all
|
||||
statements are reachable.</para>
|
||||
|
||||
<para>Here is an example:</para>
|
||||
|
||||
|
|
@ -171,8 +156,8 @@ void f2()
|
|||
"return;" statement. It will only see that if the execution reaches the
|
||||
"return;" then there will be a memory leak.</para>
|
||||
|
||||
<para>This lack of advanced control-flow analysis means that many bugs are
|
||||
not detected:</para>
|
||||
<para>Lack of advanced control-flow analysis means that many bugs are not
|
||||
detected:</para>
|
||||
|
||||
<programlisting>void f(int x)
|
||||
{
|
||||
|
|
@ -185,20 +170,21 @@ void f2()
|
|||
free(a);
|
||||
}</programlisting>
|
||||
|
||||
<para>Many other static analysis tools will probably detect that.</para>
|
||||
<para>Cppcheck doesn't detect any error. The "all conditions can be either
|
||||
true/false" means that cppcheck doesn't know that "if (x==20)" is false
|
||||
when "if (x==10)" is true. Many other static analysis tools will probably
|
||||
detect that there will be a leak if x is 10.</para>
|
||||
</section>
|
||||
|
||||
<para>Many memory leaks are caused by:</para>
|
||||
<section>
|
||||
<title>Final thoughts</title>
|
||||
|
||||
<itemizedlist>
|
||||
<listitem>
|
||||
<para>Completely forgetting to deallocate</para>
|
||||
</listitem>
|
||||
<para>You can not trust that Cppcheck will detect all bugs.</para>
|
||||
|
||||
<listitem>
|
||||
<para>Forgetting to deallocate in a bailout path</para>
|
||||
</listitem>
|
||||
</itemizedlist>
|
||||
<para>Cppcheck will just find some bugs. It is likely that you won't find
|
||||
these bugs unless you use Cppcheck. Cppcheck has found bugs in production
|
||||
code that has been used for years.</para>
|
||||
|
||||
<para>These types of leaks should be detected by Cppcheck.</para>
|
||||
<para></para>
|
||||
</section>
|
||||
</article>
|
||||
Loading…
Reference in New Issue