让Valgrind满意

Question

int main(int argc, char* argv[]) 
{
   string s1 = "String";
   char *s2 = strdup(s1.c_str());
   free(s2);
   return 0;
}

Valgrind在上面发布的代码中报告了以下内容：

==29608== Conditional jump or move depends on uninitialised value(s)
==29608==    at 0x41F9049: ??? (in /usr/local/lib/libc.so.6)
==29608==    by 0x41F8C25: strdup (in /usr/local/lib/libc.so.6)
==29608==    by 0x804D704: main

Valgrind在抱怨什么？我可以安全地忽略这个错误吗？