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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 --- - bad fixit for Wstrncat-size in macro"
href="http://llvm.org/bugs/show_bug.cgi?id=17200">17200</a>
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<tr>
<th>Summary</th>
<td>bad fixit for Wstrncat-size in macro
</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>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<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>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nlewycky@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Example:
nlewycky@ducttape:~$ llvm/Debug+Asserts/bin/clang -fsyntax-only strncat-macro.c
In file included from strncat-macro.c:1:
./strncat-hdr.h:6:24: warning: the value of the size argument in 'strncat' is
too large, might lead to a buffer overflow [-Wstrncat-size]
(strncat((A), (B), sizeof(A)-strlen(A)), *((A)+sizeof(A)-1) = '\0')
^~~~~~~~~~~~~~~~~~~
./strncat-hdr.h:5:24: note: change the argument to be the free space in the
destination buffer minus the terminating null byte
(strncat((A), (B), sizeof(A)-strlen(A)), *((A)+sizeof(A)-1) = '\0')
^~~~~~~~~~~~~~~~~~~
sizeof(dtString) - strlen(dtString) - 1
1 warning generated.
Of course writing in "dtString" for macro argument "A" isn't right. Here's the
two-file testcase:
nlewycky@ducttape:~$ cat strncat-macro.c
#include "strncat-hdr.h"
void test() {
char dtString[64];
char usecString[64];
STRSCAT(dtString, usecString);
}
nlewycky@ducttape:~$ cat strncat-hdr.h
#define strncat(dest, src, n) __builtin_strncat (dest, src, n)
unsigned long strlen(const char *s);
#define STRSCAT(A,B) \
(strncat((A), (B), sizeof(A)-strlen(A)), *((A)+sizeof(A)-1) = '\0')</pre>
</div>
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