From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id 52452385780A; Mon, 15 Nov 2021 00:20:33 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 52452385780A
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/103240] New: std::type_info::before gives wrong
 answer for ARM EABI
Date: Mon, 15 Nov 2021 00:20:33 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: ABI
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 keywords bug_severity priority component assigned_to reporter
 target_milestone cf_gcctarget
Message-ID: <bug-103240-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Mon, 15 Nov 2021 00:20:33 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103240

            Bug ID: 103240
           Summary: std::type_info::before gives wrong answer for ARM EABI
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: ABI
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---
            Target: arm*-*-*gnueabi

This passes on x86_64 but fails on armv7hl:

// f1.C
#include <typeinfo>

namespace
{
  struct S { };
}

std::type_info const& t1 =3D typeid(S);

// f2.C
#include <typeinfo>
#include <cassert>

extern std::type_info const& t1;

namespace
{
  struct S { };
}

std::type_info const& t2 =3D typeid(S);

int main()
{
  if (t1 =3D=3D t2)
  {
    assert( !t1.before(t2) );
    assert( !t2.before(t1) );
  }
  else
  {
    assert( t1.before(t2) || t2.before(t1) );
  }
}

$ g++ f1.C f2.C
$ ./a.out
a.out: f2.C:22: int main(): Assertion `t1.before(t2) || t2.before(t1)' fail=
ed.
qemu: uncaught target signal 6 (Aborted) - core dumped
Aborted (core dumped)

The problem is in libsupc++/tinfo2.cc

bool
type_info::before (const type_info &arg) const _GLIBCXX_NOEXCEPT
{
#if __GXX_MERGED_TYPEINFO_NAMES
  return name () < arg.name ();
#else
  return (name ()[0] =3D=3D '*') ? name () < arg.name ()
    :  __builtin_strcmp (name (), arg.name ()) < 0;
#endif
}

This should have been fixed like operator=3D=3D was in r179236 so that it c=
hecks
__name[0] not name()[0], otherwise the '*' is skipped and so is never found
there. That means we do a strcmp comparison of the mangled names, even when=
 the
'*' says the types must be compared by pointer address. In the testcase the=
 two
structs have the same mangled name, even though they are distinct types (du=
e to
the unnamed namespaces). The string comparison therefore returns 0, and so
neither type is "before" the other, despite being distinct types.=