[Bug c++/12176] New: Incorrect size for unions with very large bitfields

[Bug c++/12176] New: Incorrect size for unions with very large bitfields

[austern at apple dot com]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12176

           Summary: Incorrect size for unions with very large bitfields
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: austern at apple dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu

Consider the following C++ code (it has to be C++, because C imposes limits on bitfield sizes):
extern "C" int printf(const char*,...);

union abcde {
  char foo : 4096;
};

int main()
{
  abcde x;
  printf("%d\n", sizeof(x));
}

When I compile and run this program, I get the result "504".  That makes no sense.  I'm running it 
on a system with 8-bit bytes, so the size of an abcde object should be 512.  Somehow 8 bytes 
have been lost.

Note that this is a problem only with unions, not with structs.

I've seen the same behavior with every version of gcc I've tested, from 2.95 through today's 
mainline, and on both OS X and Linux.

[Bug c++/12176] [ABI] Incorrect size for unions with very large bitfields

[bangerth at dealii dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12176


bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2003-09-05 14:34:16
               date|                            |
            Summary|Incorrect size for unions   |[ABI] Incorrect size for
                   |with very large bitfields   |unions with very large
                   |                            |bitfields


------- Additional Comments From bangerth at dealii dot org  2003-09-05 14:34 -------
Confirmed. That makes it incompatible with icc, which returns 512.

W.

[Bug c++/12176] [ABI] Incorrect size for unions with very large bitfields

[austern at apple dot com]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12176


austern at apple dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |austern at apple dot com
                   |dot org                     |
             Status|NEW                         |ASSIGNED

[Bug c++/12176] [ABI] Incorrect size for unions with very large bitfields

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12176


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-09-15 00:31 -------
Fixed by:
2003-09-14  Mark Mitchell  <mark@codesourcery.com>

	* class.c (layout_class_type): Make DECL_MODE match TYPE_MODE for
	an bit-field whose width exceeds that of its type.

[Bug c++/12176] [ABI] Incorrect size for unions with very large bitfields

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12176


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-09-15 00:35 -------
That me reopen it because I did not test the patch at all, I should have might have been fixed by.

[Bug c++/12176] [ABI] Incorrect size for unions with very large bitfields

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12176


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |ASSIGNED
           Keywords|                            |wrong-code
   Target Milestone|---                         |3.4


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-09-22 08:12 -------
Still happens.

[Bug c++/12176] Incorrect size for unions with very large bitfields

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |critical
           Keywords|                            |ABI
            Summary|[ABI] Incorrect size for    |Incorrect size for unions
                   |unions with very large      |with very large bitfields
                   |bitfields                   |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12176

[Bug c++/12176] Incorrect size for unions with very large bitfields

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2003-12-30 01:10 -------
This is a problem with -fabi-version=1; it does not occur with -fabi-version=2.

Since changing the size of the union would change the version 1 ABI, and since
this kind of code is very rare, I have closed this PR.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |WONTFIX


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12176