[Bug middle-end/28160] New: Bogus "size of array 'foo' is too large" error with -mms-bitfields

[Bug middle-end/28160] New: Bogus "size of array 'foo' is too large" error with -mms-bitfields

[kkojima at gcc dot gnu dot org]

Several g++ tests in tmpdir-g++.dg-struct-layout-1 fail during
the compilation with the error message like

  error: size of array 'foo' is too large

with -mms-bitfields.  A reduced testcase is

typedef long int along __attribute__((aligned (32)));
struct S
{
  unsigned char a;
  along d:130;
  int e:66;
} A[1];

It looks the ms-bitfield code in stor-layout.c doesn't take
the bit field with excessive size into account and it makes
the negative remaining_in_alignment which causes the above
error.


-- 
           Summary: Bogus "size of array 'foo' is too large" error with -
                    mms-bitfields
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kkojima 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=28160

[Bug middle-end/28160] Bogus "size of array 'foo' is too large" error with -mms-bitfields

[seongbae dot park at gmail dot com]

------- Comment #1 from seongbae dot park at gmail dot com  2006-06-26 20:46 -------
I belive this is a bug in stor-layout.c:place_field() around line 10503
bitpos is calculated as bit_offset of rli->prev_field + type size.
However, the prev_field is not really the immediately previous field but the
first field of the consecutive same-sized fields.
Hence, in this case:

struct S
{
  long long d:23;
  int e:32;
  int f:32;
} a;

rli->prev_field is "d" when "field" is f. 
The correct fix should calculate the bitpos as 
rli->bitpos + type size.


-- 

seongbae dot park at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |seongbae dot park at gmail
                   |                            |dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28160

[Bug middle-end/28160] Bogus "size of array 'foo' is too large" error with -mms-bitfields

[seongbae dot park at gmail dot com]

------- Comment #2 from seongbae dot park at gmail dot com  2006-06-26 20:47 -------
Oops. Mu previous comment is misplaced. It should have been on PR28161. 
Please ignore it.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28160

[Bug middle-end/28160] Bogus "size of array 'foo' is too large" error with -mms-bitfields

[seongbae dot park at gmail dot com]

------- Comment #3 from seongbae dot park at gmail dot com  2006-06-26 21:08 -------
The immediate cause of the problem is in stor-layout.c:place_field():

   1118           if (DECL_SIZE (field) != NULL
   1119               && host_integerp (TYPE_SIZE (TREE_TYPE (field)), 0)
   1120               && host_integerp (DECL_SIZE (field), 0))
   1121             rli->remaining_in_alignment
   1122               = tree_low_cst (TYPE_SIZE (TREE_TYPE(field)), 1)
   1123                 - tree_low_cst (DECL_SIZE (field), 1);

For the field "d", 
remiaining_in_alignment becomes negative after line 1121-1123
- because the DECL_SIZE is larger than TYPE_SIZE for "d".


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28160

[Bug middle-end/28160] Bogus "size of array 'foo' is too large" error with -mms-bitfields

[kkojima at gcc dot gnu dot org]

------- Comment #4 from kkojima at gcc dot gnu dot org  2006-06-26 22:42 -------
Thanks for your comment. Perhaps one solution would be to handle
such bit fields with excessive sizes as the case of "no remaining
bits in alignment".  I'm testing the appended patch which changes
lines you've pointed out.

--- ORIG/trunk/gcc/stor-layout.c        2006-06-13 09:06:36.000000000 +0900
+++ LOCAL/trunk/gcc/stor-layout.c       2006-06-26 16:43:12.000000000 +0900
@@ -1047,17 +1047,20 @@ place_field (record_layout_info rli, tre

              if (rli->remaining_in_alignment < bitsize)
                {
+                 HOST_WIDE_INT typesize = tree_low_cst (TYPE_SIZE (type), 1);
+
                  /* out of bits; bump up to next 'word'.  */
-                 rli->offset = DECL_FIELD_OFFSET (rli->prev_field);
                  rli->bitpos
-                   = size_binop (PLUS_EXPR, TYPE_SIZE (type),
-                                 DECL_FIELD_BIT_OFFSET (rli->prev_field));
+                   = size_binop (PLUS_EXPR, rli->bitpos,
+                                 bitsize_int (rli->remaining_in_alignment));
                  rli->prev_field = field;
-                 rli->remaining_in_alignment
-                   = tree_low_cst (TYPE_SIZE (type), 1);
+                 if (typesize < bitsize)
+                   rli->remaining_in_alignment = 0;
+                 else
+                   rli->remaining_in_alignment = typesize - bitsize;
                }
-
-             rli->remaining_in_alignment -= bitsize;
+             else
+               rli->remaining_in_alignment -= bitsize;
            }
          else
            {
@@ -1119,9 +1121,16 @@ place_field (record_layout_info rli, tre
          if (DECL_SIZE (field) != NULL
              && host_integerp (TYPE_SIZE (TREE_TYPE (field)), 0)
              && host_integerp (DECL_SIZE (field), 0))
-           rli->remaining_in_alignment
-             = tree_low_cst (TYPE_SIZE (TREE_TYPE(field)), 1)
-               - tree_low_cst (DECL_SIZE (field), 1);
+           {
+             HOST_WIDE_INT bitsize = tree_low_cst (DECL_SIZE (field), 1);
+             HOST_WIDE_INT typesize
+               = tree_low_cst (TYPE_SIZE (TREE_TYPE (field)), 1);
+
+             if (typesize < bitsize)
+               rli->remaining_in_alignment = 0;
+             else
+               rli->remaining_in_alignment = typesize - bitsize;
+           }

          /* Now align (conventionally) for the new type.  */
          type_align = TYPE_ALIGN (TREE_TYPE (field));


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28160

[Bug middle-end/28160] Bogus "size of array 'foo' is too large" error with -mms-bitfields

[patchapp at dberlin dot org]

------- Comment #5 from patchapp at dberlin dot org  2006-06-29 21:45 -------
Subject: Bug number PR middle-end/28160

A patch for this bug has been added to the patch tracker.
The mailing list url for the patch is
http://gcc.gnu.org/ml/gcc-patches/2006-06/msg01472.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28160

[Bug middle-end/28160] Bogus "size of array 'foo' is too large" error with -mms-bitfields

[kkojima at gcc dot gnu dot org]

------- Comment #6 from kkojima at gcc dot gnu dot org  2006-07-15 06:59 -------
Subject: Bug 28160

Author: kkojima
Date: Sat Jul 15 06:58:57 2006
New Revision: 115464

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=115464
Log:
        PR middle-end/28160
        * stor-layout.c (place_field): Take the bit field with
        an excessive size into account in the ms-bitfiled case.

        PR middle-end/28161
        * stor-layout.c (place_field): Use DECL_BIT_FIELD_TYPE of
        the previous bit field.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/stor-layout.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28160

[Bug middle-end/28160] Bogus "size of array 'foo' is too large" error with -mms-bitfields

[kkojima at gcc dot gnu dot org]

------- Comment #7 from kkojima at gcc dot gnu dot org  2006-07-15 23:12 -------
Fixed.


-- 

kkojima at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28160