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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - static analyzer fails to evaluate strlen"
href="http://llvm.org/bugs/show_bug.cgi?id=18915">18915</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>static analyzer fails to evaluate strlen
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Static Analyzer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>kremenek@apple.com
</td>
</tr>
<tr>
<th>Reporter</th>
<td>ed0.88.prez@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Example from the Juliet test suite:
$ cat strlenbug.c
#include <stdlib.h>
#include <string.h>
void f()
{
char *c = (char *)malloc(100*sizeof(char));
if (!c)
return;
c[0] = '\0';
size_t cLen = strlen(c);
if (100-cLen > 1)
; //ok
else {
if (c[1] == '\0') // should not go here!
;
}
free(c);
}
EOF
When I run the analyzer I get:
$ scan-build --use-analyzer /usr/bin/clang -o buildres/ clang -c strlenbug.c -o
/dev/null > /dev/null
strlenbug.c:14:18: warning: The left operand of '==' is a garbage value
if (c[1] == '\0') // should not go here!
~~~~ ^
1 warning generated.
In the html-generated file, the analyzer takes the 'false' branch for the
condition "100-cLen > 1", which is not possible, but if I replace line 10 with
the inlined version of strlen():
size_t cLen = 0;
while(c[cLen] != '\0')
++c;
the report goes away (and alpha checker reports correctly "never executed"
warning for the expressions '++c;' and 'if (c[1] == '\0')').
Unrelated problem: if I remove the 'does malloc return null' line, I don't get
any message regarding the possible null pointer dereference in "c[0] = '\0';"
when malloc fails, even with alpha check enabled.</pre>
</div>
</p>
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