• d-bugmail puremagic.com Apr 08 2009
• d-bugmail puremagic.com Apr 09 2009
• d-bugmail puremagic.com Apr 09 2009
• d-bugmail puremagic.com May 15 2009

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2821

           Summary: struct alignment inconsistent with C for { int, long }
           Product: D
           Version: 1.043
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Keywords: wrong-code
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: kamm-removethis incasoftware.de


I couldn't find it in the spec right now, but as far as I remember D and C
structs are supposed to be aligned identically when the same types are used.

struct S {
  int i;
  long l;
}

In C (using gcc 4.1.2), the S.l.offsetof is 4 and the total size is 12. With
dmd the offsetof is 8 and the total size is 16.

Test code:
-- D code
import std.stdio;

struct S {
  int i;
  long l;
}

void main() {
  writefln("%d %d", S.sizeof, S.l.offsetof);
}
-- C code
#include <stdio.h>

struct S
{
  int i;
  long long l;
};

int main()
{
  struct S s;
  printf("%d %d\n", sizeof(s), (void*)&s.l - (void*)&s);
  return 1;
}
--


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2821


smjg iname.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |smjg iname.com




------- Comment #1 from smjg iname.com  2009-04-09 05:12 -------
Have you tried DMC and GDC to compare?

One would expect GDC to do the same as GCC, and DMD to do the same as DMC.  But
how does each decide what alignment to default to in the first place?


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2821





------- Comment #2 from tomas famolsen.dk  2009-04-09 05:33 -------
DMD on Win32 should obviously match DMC, but DMD on other platforms should
match the companion C compiler there, which is GCC.

GCC on x86-32 aligns int64 to 4 bytes (at least on Linux). There was a similar
issue with double that was fixed in 1.042:
http://d.puremagic.com/issues/show_bug.cgi?id=2692


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2821


Walter Bright <bugzilla digitalmars.com> changed:

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




--- Comment #3 from Walter Bright <bugzilla digitalmars.com>  2009-05-15
12:15:29 PDT ---
Fixed dmd 1.045 and 2.030

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