[Bug c++/20763] New: [4.0 regression] Incompatible struct alignment change

[Bug c++/20763] New: [4.0 regression] Incompatible struct alignment change

[aph at gcc dot gnu dot org]

C++ structure layout has changed and is now incompatible between C++ and Java,
and between older releases of C++.
Structure layout is also incompatible with C.

This is an ABI breaking bug.

See the discussion beginning at

http://gcc.gnu.org/ml/gcc/2005-04/msg00139.html
and the testcase at http://gcc.gnu.org/ml/gcc/2005-04/msg00152.html

-- 
           Summary: [4.0 regression] Incompatible struct alignment change
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: aph at gcc dot gnu dot org
                CC: aph at gcc dot gnu dot org,gcc-bugs at gcc dot gnu dot
                    org,pinskia at physics dot uc dot edu
 GCC build triplet: powerpc-unknown-linux-gnu
  GCC host triplet: powerpc-unknown-linux-gnu
GCC target triplet: powerpc-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20763

[Bug c++/20763] [4.0 regression] Incompatible struct alignment change

[aph at gcc dot gnu dot org]

------- Additional Comments From aph at gcc dot gnu dot org  2005-04-05 08:54 -------
Created an attachment (id=8535)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=8535&action=view)
A test case

If you run the appended code with g++ version 3.4.1, you get

 $ g++ -m32 thing.cc -save-temps && ./a.out
56

With 4.0, you get

 $ PATH=/local/aph/install/bin/:$PATH g++ -m32 thing.cc -save-temps
-fabi-version=0 && ./a.out
52


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20763

[Bug c++/20763] [4.0 regression] Incompatible struct alignment change

[jakub at gcc dot gnu dot org]

------- Additional Comments From jakub at gcc dot gnu dot org  2005-04-05 12:59 -------
typedef void *voidp;

struct S
{
  char a;
  voidp __attribute__ ((aligned (16))) b;
};

struct T
{
  char a;
  void *__attribute__ ((aligned (16))) b;
};

int f[sizeof (struct S) != sizeof (struct T) ? -1 : 1];

also fails, on all arches I tried (16 byte alignment so that it fails also
on 64-bit arches).

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20763

[Bug c++/20763] [4.0/4.1 regression] Incompatible struct alignment change

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-05 13:07 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
  GCC build triplet|powerpc-unknown-linux-gnu   |
   GCC host triplet|powerpc-unknown-linux-gnu   |
 GCC target triplet|powerpc-unknown-linux-gnu   |
           Keywords|                            |ABI, wrong-code
   Last reconfirmed|0000-00-00 00:00:00         |2005-04-05 13:07:32
               date|                            |
            Summary|[4.0 regression]            |[4.0/4.1 regression]
                   |Incompatible struct         |Incompatible struct
                   |alignment change            |alignment change
   Target Milestone|---                         |4.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20763

[Bug c++/20763] [4.0/4.1 regression] Incompatible struct alignment change

[jakub at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2005-04-05 13:07:32         |2005-04-05 13:14:01
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20763

[Bug c++/20763] [4.0/4.1 regression] Incompatible struct alignment change

[jakub at gcc dot gnu dot org]

------- Additional Comments From jakub at gcc dot gnu dot org  2005-04-05 14:04 -------
Mark, this seems to be caused by
http://gcc.gnu.org/ml/gcc-patches/2004-06/msg01720.html
The attributes are attached to the cdk_id declarator which is stored inside
of a cdk_pointer declarator, but grokdeclarator only looks at
declarator->attributes of the non-cdk_id declarators and so the attributes
get lost.
I'm not sure where is the best place to handle these, so will work on
g++.dg-struct-layout-1 testsuite which ought to catch such ABI changes instead.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu dot org
         AssignedTo|jakub at gcc dot gnu dot org|unassigned at gcc dot gnu
                   |                            |dot org
             Status|ASSIGNED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20763

[Bug c++/20763] [4.0/4.1 regression] Incompatible struct alignment change

[mmitchel at gcc dot gnu dot org]

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20763

[Bug c++/20763] [4.0/4.1 regression] Incompatible struct alignment change

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2005-04-05 17:38 -------
Fixed in 4.0.

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20763