steve@sdcc3.UUCP (Steve Serocki) (09/04/84)
Subject: PCC's Indefensible Argument Processing -- "bad arg temp" bug
Index: lib/mip/pftn.c 4.2BSD
Description:
Error checking in the portable C compiler's semantic analysis
phase has always been less than rigorous, to the point now of
being the butt of cruel jokes comparing the pcc in robustness
to the C shell. Recent ridicule (*) has been directed
especially at the comic handling of irregular parameter
declarations.
The pcc will disdain catching parameters described as "static",
or "extern" storage class in semantic analysis, ultimately
falling on its nose in codegen, or worse. A catch is described
in a companion bug report.
The pcc will often respond to missing parameters with a "bad
arg temp" warning, and then go on to generate incorrect code.
If the missing parameter is in addition (improperly) declared
"static" or "external" no warning will be given and the result
will be even more bizarre. A catch for the "bad arg temp" bug is
described here.
[(*) Refs: 3015@utah-cs.UUCP, 8180-8181@ucmp-cs.UUCP]
Repeat-By:
"bad arg temp":
Give the following C program to the pcc and compile
with the -S option. The compiler will give the "bad arg temp"
warning and display a ridiculous stack offset for
the parameter.
-------the program:------
int imp;
main(perverse )
int imp; /* "imp" missing from param list */
{
imp = 6969;
}
-------the .s file:-------
LL0:
.data
.comm _imp,4
.text
.align 1
.globl _main
_main:
.word L13
jbr L15
L16:
"foo.c", line 6: warning: bad arg temp
cvtwl $6969,-1275(ap)
ret
.set L13,0x0
L15:
jbr L16
.data
Even more bizarre:
Give the following C program to the pcc and compile
with the -S option. The compile will complete
normally and silently. L13 will be undefined in the
output.
int imp;
main(perverse )
static int imp; /* "imp" missing from param list */
{
imp = 6969;
}
Fix:
The problem seems to be an errant "if" statement sifting out
(incorrectly) cases that should be caught as errors
in the first "switch" [if...switch(class)] in defid().
The case of (blevel == 1 && { ident type not FunctionArg }
&& { ident defined somewhere though})
was not being caught. Moving the switch up and
out of the if statement solves the problem, catching
the extra cases without side effects. The changed compiler
clones itself.
*** pftn.c Sun Jul 17 13:37:05 1983
--- jess.pftn.c Tue Sep 4 04:09:07 1984
***************
*** 79,85
if( stp == FTN && p->sclass == SNULL )goto enter;
/* name encountered as function, not yet defined */
- if( stp == UNDEF|| stp == FARG ){
if( blevel==1 && stp!=FARG ) switch( class ){
default:
--- 79,84 -----
if( stp == FTN && p->sclass == SNULL )goto enter;
/* name encountered as function, not yet defined */
if( blevel==1 && stp!=FARG ) switch( class ){
default:
***************
*** 97,102
case TYPEDEF:
;
}
goto enter;
}
--- 96,103 -----
case TYPEDEF:
;
}
+
+ if( stp == UNDEF|| stp == FARG )
goto enter;
if( type != stp ) goto mismatch;
***************
*** 98,104
;
}
goto enter;
- }
if( type != stp ) goto mismatch;
/* test (and possibly adjust) dimensions */
--- 99,104 -----
if( stp == UNDEF|| stp == FARG )
goto enter;
if( type != stp ) goto mismatch;
/* test (and possibly adjust) dimensions */