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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - False positive error in memory sanitizer"
href="https://bugs.llvm.org/show_bug.cgi?id=39824">39824</a>
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<th>Summary</th>
<td>False positive error in memory sanitizer
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>7.0
</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>
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<th>Component</th>
<td>Tooling
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>gael.guennebaud@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>The following self-contained example trigger an error with memory sanitizer:
*******************************
#include <iostream>
struct Vec {
const float* data() const {return 0;}
};
struct myevaluator3 { ~myevaluator3() {} };
struct myevaluator2 : myevaluator3 {
myevaluator2(const Vec& v) : m(v.data()) {}
const float * m;
};
struct myevaluator : myevaluator2 {
myevaluator(const Vec& m) : myevaluator2(m) {}
};
float foo(const Vec&,int) {
Vec w;
myevaluator e(w);
return 0;
}
int main() {
Vec v;
float x = foo(v,0);
std::cout << x;
}
*******************************
Compiling without any optimization, i.e.,
$ clang++-7 bug.cpp -fsanitize=memory && ./a.out
gives me:
Uninitialized bytes in __interceptor_memcmp at offset 244 inside
[0x7ffeeaa581c0, 256)
==10014==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x7f2b3838ce2b in std::ctype<char>::_M_widen_init() const
(/usr/lib/x86_64-linux-gnu/libstdc++.so.6+0xb8e2b)
#1 0x7f2b383e8df7 in std::ostream& std::ostream::_M_insert<double>(double)
(/usr/lib/x86_64-linux-gnu/libstdc++.so.6+0x114df7)
#2 0x49445c in main (a.out+0x49445c)
#3 0x7f2b37323b96 in __libc_start_main
/build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310
#4 0x41b4d9 in _start (a.out+0x41b4d9)
This is the most reduced test case I managed to get. For instance any of the
following change will remove the reported error:
- remove the destructor ~myevaluator3() {}
- reduce the hierarchy of myevaluator
- change the prototype of foo to: float foo(const Vec&) or float foo(Vec,int)
- removing std::cout << x;
- ...
The reported error also goes away if compiling with -O1 or higher.
I hope I did not reported a false negative ;)</pre>
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