wescott@sauron.UUCP (Mike Wescott) (11/24/86)
There is a bug in print.c (version 1.1). Unfortunately this section of code
has had a patch posted for it recently. In the original code, the problem is
masked for most architectures (VAX sizes and alignments) because a null
pointer is fetched and subsequently ignored. On some mc680x0 implementations,
the layout of class fct and class basetype do not line up quite right and
instead of a null pointer the top half of another pointer is fetched. The
problem shows up when running main.c through cfront.
On VAX-like machines the bug can be demonstrated by the following code:
typedef int (*ST)(float);
extern ST s;
x()
{
(*s)(4);
s(4);
}
which produces (cleaned up and beautified):
/* <<cfront 05/20/86>> */
int *_new ();
int _delete ();
int *_vec_new ();
int _vec_delete ();
typedef int (*ST )();
extern ST s ;
int x ()
{
(*s )( (float )4 ) ;
s( 4 ) ;
};
Note the lack of a cast in the second call to `s'. Since both calls are
equivalent. The resulting code should be as well. This is the best result.
On my machine an internal error (bus error) occured. The recent fix to
print.c causes different problems. I think that the following patch covers
all bases. The fix was supplied by Dr. Stroustrup with permission to post
it:
*** print.c.orig Mon Nov 24 12:15:19 1986
--- print.c Mon Nov 24 12:16:07 1986
***************
*** 1371,1380
}
else {
//error('d',"e1%k e1->tp %d %d%t",e1->base,e1->tp,e1->tp->base,e1->tp);
! eprint(e1);
! if (e1->tp) // pointer to fct
! at = Pfct(e1->tp)->argtype;
! else // virtual: argtype encoded
at = (Pname)e1->e1->tp;
}
puttok(LP);
--- 1371,1394 -----
}
else {
//error('d',"e1%k e1->tp %d %d%t",e1->base,e1->tp,e1->tp->base,e1->tp);
! Pfct f = Pfct(e1->tp);
! // eprint(e1);
! if (f) { // pointer to fct
! while (f->base == TYPE) f = Pfct(Pbase(f)->b_name->tp);
! if (f->base == PTR) {
! putstring("(*");
! e1->print();
! putch(')');
! f = Pfct(Pptr(f)->typ);
! while (f->base == TYPE) f = Pfct(Pbase(f)->b_name->tp);
! }
! else
! eprint(e1);
!
! at = (f->f_result) ? f->f_result : f->argtype;
! }
! else { // virtual: argtype encoded
! eprint(e1);
at = (Pname)e1->e1->tp;
}
}
***************
*** 1376,1381
at = Pfct(e1->tp)->argtype;
else // virtual: argtype encoded
at = (Pname)e1->e1->tp;
}
puttok(LP);
if (e2) {
--- 1390,1396 -----
else { // virtual: argtype encoded
eprint(e1);
at = (Pname)e1->e1->tp;
+ }
}
puttok(LP);
if (e2) {
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-
The second bug is in error.c. The version 1.1 code for the function error()
fetches too much from the stack when it calls the canonical form of error().
The bug is exemplified by this piece of error.c:
int error(char* s ...)
{
register Pname a = Pname(((char*)&s)+sizeof(char*));
return error(0,&dummy_loc,s,a[0],a[1],a[2],a[3],a[4],a[5],a[6],a[7]);
}
The variable a is type ``pointer to struct name'' and is initialized to an
address in the argument stack. Therefore a[x] is type ``struct name'' and the
code error(...,a[0],a[1],a[2],a[3],a[4],a[5],a[6],a[7]) passes 8
structures, not 8 pointers to structures. The upshot of all of this is that
roughly 640 bytes are fetched from the stack and passed again to error. If
your environment is small or the call to error happens when the stack has not
grown big enough, unexpected ``internal error'' can occur, even dump core.
This explains why several types of errors will produce the internal error on
one machine and seem to work fine on others. It all depends on the size of
the stack when the error occurs.
Dr. Stroustrup has indicated that version 1.2 will have a much different
error.c, so I conjured up this patch which changes the Pname to char** in
the appropriate places.
*** error.c.orig Mon Nov 24 12:15:49 1986
--- error.c Mon Nov 24 12:16:07 1986
***************
*** 102,108
int error(char* s ...)
{
! register Pname a = Pname(((char*)&s)+sizeof(char*));
return error(0,&dummy_loc,s,a[0],a[1],a[2],a[3],a[4],a[5],a[6],a[7]);
}
--- 102,108 -----
int error(char* s ...)
{
! register char** a = (char **)(((char*)&s)+sizeof(char*));
return error(0,&dummy_loc,s,a[0],a[1],a[2],a[3],a[4],a[5],a[6],a[7]);
}
***************
*** 108,114
int error(int t, char* s ...)
{
! register Pname a = Pname(((char*)&s)+sizeof(char*));
return error(t,&dummy_loc,s,a[0],a[1],a[2],a[3],a[4],a[5],a[6],a[7]);
}
--- 108,114 -----
int error(int t, char* s ...)
{
! register char** a = (char **)(((char*)&s)+sizeof(char*));
return error(t,&dummy_loc,s,a[0],a[1],a[2],a[3],a[4],a[5],a[6],a[7]);
}
***************
*** 114,120
int error(loc* l, char* s ...)
{
! register Pname a = Pname(((char*)&s)+sizeof(char*));
return error(0,l,s,a[0],a[1],a[2],a[3],a[4],a[5],a[6],a[7]);
}
--- 114,120 -----
int error(loc* l, char* s ...)
{
! register char** a = (char **)(((char*)&s)+sizeof(char*));
return error(0,l,s,a[0],a[1],a[2],a[3],a[4],a[5],a[6],a[7]);
}
--
-Mike Wescott
ncrcae!wescott