[Mono-bugs] [Bug 375160] New: Wrong struct packing.

[bugzilla_noreply at novell.com]

https://bugzilla.novell.com/show_bug.cgi?id=375160


           Summary: Wrong struct packing.
           Product: Mono: Runtime
           Version: SVN
          Platform: x86-64
        OS/Version: Linux
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: interop
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: jan.oravec at 6com.sk
         QAContact: mono-bugs at lists.ximian.com
          Found By: ---


Let's have structures (on x86-64):

[ StructLayout (LayoutKind.Sequential, Pack = 8) ]
unsafe struct X
{
  fixed int x[N];   // fixed-size buffer used only for convenience
}

[ StructLayout (LayoutKind.Sequential, Pack = 8) ]
struct Y
{
  int a;
  X x;
}


Mono makes this packing:

N    sizeof (X)     sizeof (Y)
1    4              8
2    8              16 (Wrong!)
3    12             16
4    16             20
5    20             24
..

Special case N = 2 produces wrong result, which makes interoperability problems
with legacy C code. sizeof (Y) = 12 is expected, as struct X doesn't contain
any fields with 8-byte alignment requirements (N = 4 produces correct result).


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