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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Missing warning about uninitialized var when going through a pointer"
href="https://llvm.org/bugs/show_bug.cgi?id=28249">28249</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missing warning about uninitialized var when going through a pointer
</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>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>ch3root@openwall.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Source code:
----------------------------------------------------------------------
#include <stdio.h>
int main()
{
int i;
printf("%d\n", *(int *)&i);
}
----------------------------------------------------------------------
Results:
----------------------------------------------------------------------
$ clang -std=c11 -Weverything -O3 test.c && ./a.out
-1069783944
----------------------------------------------------------------------
clang version: clang version 3.9.0 (trunk 271312)
For comparison:
----------------------------------------------------------------------
$ gcc -std=c11 -pedantic -Wall -Wextra -O3 test.c && ./a.out
test.c: In function ‘main’:
test.c:6:3: warning: ‘i’ is used uninitialized in this function
[-Wuninitialized]
printf("%d\n", *(int *)&i);
^~~~~~~~~~~~~~~~~~~~~~~~~~
0
----------------------------------------------------------------------
gcc version: gcc (GCC) 7.0.0 20160616 (experimental)
The optimizer sees that an undef value is used:
----------------------------------------------------------------------
*** IR Dump After SROA ***
; Function Attrs: nounwind uwtable
define i32 @main() #0 {
entry:
%call = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4
x i8]* @.str, i32 0, i32 0), i32 undef)
ret i32 0
}
----------------------------------------------------------------------
but nevertheless a warning is not emitted.
The code in the testcase is useless but the same happens when a representation
of an uninitialized variable is accessed, i.e. there is no warning for `*(char
*)&i`.</pre>
</div>
</p>
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