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PDP10: Fix nested indirect address limit exceeded (from Bob Supnik)

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If the nested indirect/execute limit (INDMAX, XCTMAX) is set to 0, the simulator will loop indefinitely in an indirect address or execute loop, testing for interrupts before each memory reference. Thus, on an infinite loop, the simulator will never complete the instruction, but the instruction is interruptible. So for example, under TOPS-10:

.r ddt
1/    0    jrstf @1
1$g
^C
^C
.

The JRSTF will never finish, but it can be interrupted by any device, and double ^C will return control to the command line.

If INDMAX or XCTMAX is non-zero, the previous behavior of limiting loops to a specific depth is retained. However, the default value is now 0.

This closes issue #218.

Conflicts:
	doc/pdp10_doc.doc
This commit is contained in:
Mark Pizzolato 2016-02-19 12:28:56 -08:00
parent 5ffd11c636
commit 92fe35fb9c
3 changed files with 49 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
PDP10/pdp10_bug_history.txt
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@ -23,3 +23,6 @@ Bugs Found and Fixed During Simulator Debug
16. RHCS1: writing IE cannot trigger an interrupt
17. Tape bootstrap was set to 800bpi instead of 1600bpi
18. FIXR off by 1 in testing for lower limit to process
19. Indirect loops and XCT loops should run indefinitely,
test for interrupts on each memory reference

68
PDP10/pdp10_cpu.c
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@ -1,6 +1,6 @@
/* pdp10_cpu.c: PDP-10 CPU simulator
Copyright (c) 1993-2012, Robert M. Supnik
Copyright (c) 1993-2016, Robert M. Supnik
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the "Software"),
@ -25,6 +25,7 @@
cpu KS10 central processor
09-Feb-16 RMS Fixed nested indirects and executes (Tim Litt)
25-Mar-12 RMS Added missing parameters to prototypes (Mark Pizzolato)
17-Jul-07 RMS Fixed non-portable usage in SHOW HISTORY
28-Apr-07 RMS Removed clock initialization
@ -191,8 +192,8 @@ int32 flags = 0; /* flags */
int32 its_1pr = 0; /* ITS 1-proceed */
int32 stop_op0 = 0; /* stop on 0 */
int32 rlog = 0; /* extend fixup log */
int32 ind_max = 32; /* nested ind limit */
int32 xct_max = 32; /* nested XCT limit */
int32 ind_max = 0; /* nested ind limit */
int32 xct_max = 0; /* nested XCT limit */
int32 t20_idlelock = 0; /* TOPS-20 idle lock */
a10 pcq[PCQ_SIZE] = { 0 }; /* PC queue */
int32 pcq_p = 0; /* PC queue ptr */
@ -388,8 +389,8 @@ REG cpu_reg[] = {
{ FLDATA (F1PR, its_1pr, 0) },
{ BRDATA (PCQ, pcq, 8, VASIZE, PCQ_SIZE), REG_RO+REG_CIRC },
{ ORDATA (PCQP, pcq_p, 6), REG_HRO },
{ DRDATA (INDMAX, ind_max, 8), PV_LEFT + REG_NZ },
{ DRDATA (XCTMAX, xct_max, 8), PV_LEFT + REG_NZ },
{ DRDATA (INDMAX, ind_max, 8), PV_LEFT },
{ DRDATA (XCTMAX, xct_max, 8), PV_LEFT },
{ ORDATA (WRU, sim_int_char, 8) },
{ FLDATA (STOP_ILL, stop_op0, 0) },
{ BRDATA (REG, acs, 8, 36, AC_NUM * AC_NBLK) },
@ -857,17 +858,23 @@ its_2pr = its_1pr; /* save 1-proc flag */
XCT:
op = GET_OP (inst); /* get opcode */
ac = GET_AC (inst); /* get AC */
for (indrct = inst, i = 0; i < ind_max; i++) { /* calc eff addr */
for (indrct = inst, i = 0; ; i++) { /* calc eff addr */
ea = GET_ADDR (indrct);
xr = GET_XR (indrct);
if (xr)
ea = (ea + ((a10) XR (xr, MM_EA))) & AMASK;
if (TST_IND (indrct))
indrct = Read (ea, MM_EA);
if (TST_IND (indrct)) { /* indirect? */
if (i != 0) { /* not first cycle? */
int32 t = test_int (); /* test for intr */
if (t != 0) /* err or intr? */
ABORT (t);
if ((ind_max != 0) && (i >= ind_max)) /* limit exceeded? */
ABORT (STOP_IND);
}
indrct = Read (ea, MM_EA); /* fetch indirect */
}
else break;
}
if (i >= ind_max)
ABORT (STOP_IND); /* too many ind? stop */
if (hst_lnt) { /* history enabled? */
hst_p = (hst_p + 1); /* next entry */
if (hst_p >= hst_lnt)
@ -1072,10 +1079,15 @@ case 0255: if (flags & (ac << 14)) { /* JFCL */
CLRF (ac << 14);
}
break;
case 0256: if (xct_cnt++ >= xct_max) /* XCT */
ABORT (STOP_XCT);
inst = Read (ea, MM_OPND);
if (ac && !TSTF (F_USR) && !Q_ITS)
case 0256: if (xct_cnt++ != 0) { /* XCT: not first? */
int32 t = test_int (); /* test for intr */
if (t != 0) /* intr or err? */
ABORT (t);
if ((xct_max != 0) && (xct_cnt >= xct_max))
ABORT (STOP_XCT);
}
inst = Read (ea, MM_OPND); /* get opnd */
if (ac && !TSTF (F_USR) && !Q_ITS) /* PXCT? */
pflgs = pflgs | ac;
goto XCT;
case 0257: if (Q_ITS) goto MUUO; /* MAP */
@ -1831,17 +1843,23 @@ a10 calc_ea (d10 inst, int32 prv)
int32 i, ea, xr;
d10 indrct;
for (indrct = inst, i = 0; i < ind_max; i++) {
for (indrct = inst, i = 0; ; i++) {
ea = GET_ADDR (indrct);
xr = GET_XR (indrct);
if (xr)
ea = (ea + ((a10) XR (xr, prv))) & AMASK;
if (TST_IND (indrct))
if (TST_IND (indrct)) { /* indirect? */
if (i != 0) { /* not first cycle? */
int32 t = test_int (); /* test for intr */
if (t != 0) /* intr or error? */
ABORT (t);
if ((ind_max != 0) && (i >= ind_max)) /* limit exceeded? */
ABORT (STOP_IND);
}
indrct = Read (ea, prv);
}
else break;
}
if (i >= ind_max)
ABORT (STOP_IND);
return ea;
}
@ -1882,17 +1900,23 @@ d10 calc_jrstfea (d10 inst, int32 pflgs)
int32 i, xr;
d10 mb;
for (i = 0; i < ind_max; i++) {
for (i = 0; ; i++) {
mb = inst;
xr = GET_XR (inst);
if (xr)
mb = (mb & AMASK) + XR (xr, MM_EA);
if (TST_IND (inst))
if (TST_IND (inst)) { /* indirect? */
if (i != 0) { /* not first cycle? */
int32 t = test_int (); /* test for intr */
if (t != 0) /* intr or error? */
ABORT (t);
if ((ind_max != 0) && (i >= ind_max)) /* limit exceeded? */
ABORT (STOP_IND);
}
inst = Read (((a10) mb) & AMASK, MM_EA);
}
else break;
}
if (i >= ind_max)
ABORT (STOP_IND);
return (mb & DMASK);
}

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