<html>
    <head>
      <base href="https://bugs.llvm.org/">
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - Libc++ is not Implicit Integer Truncation Sanitizer clean"
   href="https://bugs.llvm.org/show_bug.cgi?id=40566">40566</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Libc++ is not Implicit Integer Truncation Sanitizer clean
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>libc++
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>unspecified
          </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>enhancement
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>All Bugs
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>eugeni.stepanov@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
          </td>
        </tr></table>
      <p>
        <div>
        <pre>#include <sstream>

int main() {
  std::stringstream ss;
  ss.write("\xd1", 1);
}


with -fsanitize=implicit-signed-integer-truncation gives:

include/c++/v1/sstream:561:28: runtime error: implicit conversion from type
'std::__1::basic_stringbuf<char, std::__1::char_traits<char>,
std::__1::allocator<char> >::int_type' (aka 'int') of value 209 (32-bit,
signed) to type 'std::__1::basic_streambuf<char, std::__1::char_traits<char>
<span class="quote">>::char_type' (aka 'char') changed the value to -47 (8-bit, signed)</span >


basic_stringbuf::overflow converts an int, which is the result of char ->
unsigned char -> int conversion, directly to (signed) char.</pre>
        </div>
      </p>


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