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      <base href="https://llvm.org/bugs/" />
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    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - Naked functions that return values are broken"
   href="https://llvm.org/bugs/show_bug.cgi?id=27230">27230</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Naked functions that return values are broken
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>3.7
          </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>hausen@gmx.at
          </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>Naked functions that return values are compiled incorrectly as soon as
optimizations are turned on. Take the following example:

int foo(void) __attribute__((naked,noinline));
int foo(void) {
  // assembly as generated for "return 41;"
  asm volatile("mov $41,%%eax; retq" : : : "memory");
}
int main() {
  return foo()+1;
}

The program returns the intended value of 42 when compiling with -O0. With -O1
however, the call to foo is replaced with a jump and the program returns 41.

As far as I can tell, the issue is caused by the fact that the end of a naked
functions is "unreachable". This seems to cause optimization passes to make
incorrect assumptions about the behavior of such functions.</pre>
        </div>
      </p>
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