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

["rsandifo at gcc dot gnu dot org" <gcc-bugzilla 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