housel@ea.ecn.purdue.edu (Peter S. Housel) (10/20/87)
Problem:
On machines with a non-Vax-byteorder, the pascal compiler
(pc) attempts to realign small structures 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,
which obviously doesn't have the problem.
*** fhdr.c.old Mon Oct 19 17:43:22 1987
--- fhdr.c Mon Oct 19 17:44:50 1987
***************
*** 383,393 ****
# ifdef PC
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;
--- 383,393 ----
# ifdef PC
o = roundup(o, (long) A_STACK);
w = lwidth(p);
! # ifdef vax
if (w <= sizeof(int)) {
o += sizeof(int) - w;
}
! # endif vax
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