housel@ea.ecn.purdue.edu (Peter S. Housel) (11/10/87)
Problem:
On machines with a non-Vax-byteorder, the pascal compiler
(pc) attempts to realign small (<=sizeof(int)) structures, arrays, and
strings when they are passed by value. Unfortunately, this realignment
only happens in the called procedure and not in the function call, so
accesses to fields within the structure get the wrong bytes.
Repeat-By:
Run the following program. It fails (prints two different
values) on some machines with big-endian byteorder, such as the
Gould 9080 or CCI 6/32. It does not fail on a Sun, but we don't
have Sun pascal source so I can't tell why.
-----------------cut--------------------
program pgm(output);
type foo = record bar:1..10 end;
var pos : foo;
procedure killer(arg : foo);
begin writeln('arg=',arg.bar) end;
begin
pos.bar := 2;
writeln('pos=', pos.bar);
killer(pos);
end.
-----------------cut--------------------
Fix:
Apply the following patch to /usr/src/ucb/pascal/src/fhdr.c, BY HAND.
This diff is relative to the VAX version; the patch works on the VAX but is
probably not strictly necessary.
*** fhdr.c.old Tue Nov 10 08:38:35 1987
--- fhdr.c Tue Nov 10 08:41:25 1987
***************
*** 384,393 ****
o = roundup(o, (long) A_STACK);
w = lwidth(p);
# ifndef DEC11
! if (w <= sizeof(int)) {
! o += sizeof(int) - w;
! }
! # endif not DEC11
dp = defnl((char *) idlist->list_node.list,VAR,
p, o);
o += w;
--- 384,400 ----
o = roundup(o, (long) A_STACK);
w = lwidth(p);
# ifndef DEC11
! switch(classify(p)) {
! case TFILE: /* these should not */
! case TARY: /* be realigned... */
! case TREC: /* pushed with STARG */
! case TSET:
! case TSTR: break;
! default: if (w <= sizeof(int)) {
! o += sizeof(int) - w;
! }
! }
! # endif !DEC11
dp = defnl((char *) idlist->list_node.list,VAR,
p, o);
o += w;
-------------------------------------------------------------------------------
Peter S. Housel housel@ei.ecn.purdue.edu
{decvax,uiucdcs,inuxc}!pur-ee!housel