[Bug c/25805] New: Incorrect handling of zero-initialized flexible arrays

[Bug c/25805] New: Incorrect handling of zero-initialized flexible arrays

[rsandifo at gcc dot gnu dot org]

A GNU C extension allows you to initialise a flexible array field.
However, if you do this, the DECL_SIZE of the containing object does not
account for the size of the initialised array.  DECL_SIZE is simply
CHAR_BIT * sizeof (the structure type).  Thus if you have:

    struct { int a; int x[]; } d1 = { 0, 0 };

and if -fzero-initialized-in-bss is in effect, we will only allocate
one int for d1, not two:

d1:
        .zero   4

A simple executable testcase is:

-------------------------------------------------
struct { int a; int x[]; } d1 = { 0, 0 };
int d2 = 0;
int main ()
{
  d2 = 1;
  if (d1.x[0] != 0)
    abort ();
  exit (0);
}
-------------------------------------------------

The testcase passes if compiled with -fno-zero-initialized-in-bss.


-- 
           Summary: Incorrect handling of zero-initialized flexible arrays
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rsandifo 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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25805

[Bug c/25805] Incorrect handling of zero-initialized flexible arrays

[rsandifo at gcc dot gnu dot org]

------- Comment #1 from rsandifo at gcc dot gnu dot org  2006-01-16 10:19 -------
Testing a fix


-- 

rsandifo at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rsandifo at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2006-01-16 10:19:50
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25805

[Bug c/25805] [3.4/4.0/4.1/4.2 Regression] Incorrect handling of zero-initialized flexible arrays

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
      Known to fail|                            |4.1.0 4.0.0 3.3.3 3.4.0
                   |                            |4.2.0
      Known to work|                            |3.2.3
            Summary|Incorrect handling of zero- |[3.4/4.0/4.1/4.2 Regression]
                   |initialized flexible arrays |Incorrect handling of zero-
                   |                            |initialized flexible arrays
   Target Milestone|---                         |4.0.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25805

[Bug c/25805] [3.4/4.0/4.1/4.2 Regression] Incorrect handling of zero-initialized flexible arrays

[rsandifo at gcc dot gnu dot org]

------- Comment #2 from rsandifo at gcc dot gnu dot org  2006-01-19 07:45 -------
Subject: Bug 25805

Author: rsandifo
Revision: 109947
Modified property: svn:log

Modified: svn:log at Thu Jan 19 07:45:28 2006
------------------------------------------------------------------------------
--- svn:log (original)
+++ svn:log Thu Jan 19 07:45:28 2006
@@ -1,1 +1,7 @@
-/home/richard/patches/wip/flex-array-init-size.clog
+       PR c/25805
+       * c-decl.c (add_flexible_array_elts_to_size): New function.
+       (finish_decl): Use it.
+
+testsuite/
+       PR c/25805
+       * gcc.dg/pr25805.c: New file.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25805

[Bug c/25805] [3.4/4.0/4.1/4.2 Regression] Incorrect handling of zero-initialized flexible arrays

[rsandifo at gcc dot gnu dot org]

------- Comment #3 from rsandifo at gcc dot gnu dot org  2006-01-19 07:46 -------
Subject: Bug 25805

Author: rsandifo
Revision: 109946
Modified property: svn:log

Modified: svn:log at Thu Jan 19 07:46:15 2006
------------------------------------------------------------------------------
--- svn:log (original)
+++ svn:log Thu Jan 19 07:46:15 2006
@@ -1,1 +1,7 @@
-/home/richard/patches/wip/flex-array-init-size.clog
+       PR c/25805
+       * c-decl.c (add_flexible_array_elts_to_size): New function.
+       (finish_decl): Use it.
+
+testsuite/
+       PR c/25805
+       * gcc.dg/pr25805.c: New file.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25805

[Bug c/25805] [3.4/4.0 Regression] Incorrect handling of zero-initialized flexible arrays

[rsandifo at gcc dot gnu dot org]

------- Comment #4 from rsandifo at gcc dot gnu dot org  2006-01-19 07:48 -------
I've checked in the fix for 4.1 and 4.2.  It doesn't apply directly
to earlier branches because they used TREE_LISTs for CONSTRUCTORs.
A straight-forward conversion would introduce a linear walk over
the list, which is probably not acceptable.  I'm leaving this is
a 3.4 and 4.0 regression for now.

(The original commit wasn't added to bugzilla because I used
-m rather than -F to specify the log message.  Ooops.  Now fixed
with svn propset.)


-- 

rsandifo at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rsandifo at gcc dot gnu dot
                   |                            |org
         AssignedTo|rsandifo at gcc dot gnu dot |unassigned at gcc dot gnu
                   |org                         |dot org
             Status|ASSIGNED                    |NEW
      Known to fail|4.1.0 4.0.0 3.3.3 3.4.0     |4.0.0 3.3.3 3.4.0
                   |4.2.0                       |
      Known to work|3.2.3                       |3.2.3 4.1.0 4.2.0
            Summary|[3.4/4.0/4.1/4.2 Regression]|[3.4/4.0 Regression]
                   |Incorrect handling of zero- |Incorrect handling of zero-
                   |initialized flexible arrays |initialized flexible arrays


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25805

[Bug c/25805] [3.4/4.0 Regression] Incorrect handling of zero-initialized flexible arrays

[mmitchel at gcc dot gnu dot org]

------- Comment #5 from mmitchel at gcc dot gnu dot org  2006-02-27 20:25 -------
Marked as P2.  This is a serious issue for those it affects, but it is indeed a
corner case.  Also, since this was broken from 3.3.x forwards, there is
presumably relatively little code using the construct; certainly, for 4.0.x,
this bug will not be preventing upgrades from previous 4.0.x releases.


-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25805

[Bug c/25805] [3.4/4.0 Regression] Incorrect handling of zero-initialized flexible arrays

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.0.3                       |4.0.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25805