Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!zazen!psl.wisc.edu!khan
From: khan@pslu1.psl.wisc.edu (Mumit Khan)
Newsgroups: comp.unix.ultrix
Subject: auto-increment bug in Ultrix(4.1) C (DS3100)
Message-ID: <1991Mar31.214127.5224@pslu1.psl.wisc.edu>
Date: 31 Mar 91 21:41:27 GMT
Reply-To: khan@xraylith.wisc.edu (Mumit Khan)
Distribution: usa
Organization: Center for X-ray Lithography
Lines: 69


 ---------------- MIPS C bug in post-increment of variables ----------
 MACHINE = DS3100
 OS = ULTRIX V4.1 (Rev. 52) System #1: Wed Dec 19 15:20:46 CST 1990
      UWS V4.1 (Rev. 197)

Note the output from the following program in various cases. MIPS C is 
the only one causing the problem (of not incrementing the global shared
variable "pc" in the call (*(*pc++))().

------------------------ START OF PROGRAM ---------------------------
#include <stdio.h>

typedef int (*Inst)();
#define StopInst (Inst) 0
static int dummy ();
static Inst machine[] = {dummy, dummy, dummy, dummy, dummy, StopInst};
static Inst *pc = NULL;

main () {
    extern int start;
    fprintf (stderr, "Starting pc: %x\n", pc = machine);
    for (; *pc != StopInst;)
	(*(*pc++)) ();		/* BUG BUG BUG BUG BUG BUG BUG */
}
static int dummy () {
    extern Inst *pc;
    fprintf (stderr, "PC (in dummy): %x\n", pc);
    return 0;
}


------------------------- END OF PROGRAM ------------------------

OUTPUT FROM MIPS CC. (Version 2.1)
> bug-mips-cc

Starting pc: 10000430
PC (in dummy): 10000430			<--- NOTE *NO* INCREMENT
PC (in dummy): 10000434
PC (in dummy): 10000438
PC (in dummy): 1000043c
PC (in dummy): 10000440
 

OUTPUT FROM MIPS GCC. (Version 2.1)
> gcc -v
gcc version 1.37.1 OSF 1.9.2.14 Ultrix Dec Mips Dec 29 1990
> bug-mips-gcc

Starting pc: 10000460
PC (in dummy): 10000464			<--- NOTE INCREMENT
PC (in dummy): 10000468
PC (in dummy): 1000046c
PC (in dummy): 10000470
PC (in dummy): 10000474


OUTPUT FROM SparcStation (IPC) CC. (SunOS rel. 4.1.1)
> bug-sun4-cc

Starting pc: 40a8
PC (in dummy): 40ac 			<--- NOTE INCREMENT
PC (in dummy): 40b0
PC (in dummy): 40b4
PC (in dummy): 40b8
PC (in dummy): 40bc

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