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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Control Flow Guard on a simple program causes a crash"
href="https://bugs.llvm.org/show_bug.cgi?id=39517">39517</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Control Flow Guard on a simple program causes a crash
</td>
</tr>
<tr>
<th>Product</th>
<td>lld
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Windows NT
</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>All Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>charles.milette@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, peter.smith@linaro.org
</td>
</tr></table>
<p>
<div>
<pre>When compiling the following program
#include <iostream>
#include <sstream>
int main()
{
std::wostringstream str;
str << L"Lorem ipsum dolor sit amet";
std::wcout << str.str();
}
using the following commands
clang-cl /c control-bug.cpp -m32 /guard:cf /MDd
--- OR ---
clang-cl /c control-bug.cpp -m32 /guard:cf /MD
lld-link /guard:cf control-bug.obj
will cause a binary that crashes before printing Lorem Ipsum to the command
prompt.
Using the static (/MT and /MTd) over the DLL (/MD and /MDd) Microsoft Runtime
Library will make a correctly working executable, as well as replacing lld-link
by link and/or clang-cl by cl.
After further debugging by setting a breakpoint on the failing
_guard_check_icall_fptr call in x32dbg, it seems that
std::basic_streambuf<unsigned short, std::char_traits<unsigned short>>::sputn
(which is a function embedded in the MS Runtime library) is calling
std::basic_streambuf<unsigned short, std::char_traits<unsigned short>>::xsputn
(which is a function embedded in the main executable file) by function pointer
but it is not registered as a valid call target to Control Flow Guard.</pre>
</div>
</p>
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