[Bug libstdc++/66624] New: libstdc++ iostream uninitialized data

["doko at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66624

            Bug ID: 66624
           Summary: libstdc++ iostream uninitialized data
           Product: gcc
           Version: 5.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: doko at gcc dot gnu.org
  Target Milestone: ---

[forwarded from https://bugs.debian.org/789369]

richard@deodand:~/junk$ cat t.cc
#include <iostream>

int main() {
  std::cout << std::hex;
  return 0;
}
richard@deodand:~/junk$ clang++-3.6 -fsanitize=undefined -O0
-fno-optimize-sibling-calls -fno-omit-frame-pointer -g -o t t.cc
richard@deodand:~/junk$ ./t
/usr/bin/../lib/gcc/i586-linux-gnu/5.1.1/../../../../include/c++/5.1.1/bits/ios_base.h:102:24:
runtime error: load of value 4294967221, which is not a valid value for
type 'std::_Ios_Fmtflags'
/usr/bin/../lib/gcc/i586-linux-gnu/5.1.1/../../../../include/c++/5.1.1/bits/ios_base.h:82:67:
runtime error: load of value 4294967221, which is not a valid value for
type 'std::_Ios_Fmtflags'

As far as I can see the problem here is that ios_base::_M_flags is never
initialized.