From e7a934904c144c8b26f24a4c08d9ef15731b2830 Mon Sep 17 00:00:00 2001
From: Mark Pizzolato <mark@infocomm.com>
Date: Thu, 17 Apr 2014 13:07:37 -0700
Subject: [PATCH] PDP11: Added support for the NEXT command to step over
 subroutine calls.

---
 PDP11/pdp11_cpu.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/PDP11/pdp11_cpu.c b/PDP11/pdp11_cpu.c
index b0e6ae4e..e759aed2 100644
--- a/PDP11/pdp11_cpu.c
+++ b/PDP11/pdp11_cpu.c
@@ -312,6 +312,7 @@ extern CPUTAB cpu_tab[];
 t_stat cpu_ex (t_value *vptr, t_addr addr, UNIT *uptr, int32 sw);
 t_stat cpu_dep (t_value val, t_addr addr, UNIT *uptr, int32 sw);
 t_stat cpu_reset (DEVICE *dptr);
+t_bool cpu_is_pc_a_subroutine_call (t_addr **ret_addrs);
 t_stat cpu_set_hist (UNIT *uptr, int32 val, char *cptr, void *desc);
 t_stat cpu_show_hist (FILE *st, UNIT *uptr, int32 val, void *desc);
 t_stat cpu_show_virt (FILE *st, UNIT *uptr, int32 val, void *desc);
@@ -3019,10 +3020,43 @@ if (pcq_r)
     pcq_r->qptr = 0;
 else return SCPE_IERR;
 sim_brk_types = sim_brk_dflt = SWMASK ('E');
+sim_vm_is_subroutine_call = &cpu_is_pc_a_subroutine_call;
 set_r_display (0, MD_KER);
 return SCPE_OK;
 }
 
+t_bool cpu_is_pc_a_subroutine_call (t_addr **ret_addrs)
+{
+#define MAX_SUB_RETURN_SKIP 10
+static t_addr returns[MAX_SUB_RETURN_SKIP + 1] = {0};
+
+if (SCPE_OK != get_aval (PC, &cpu_dev, &cpu_unit))      /* get data */
+    return FALSE;
+if ((sim_eval[0] & 0177000) == 0004000) {               /* JSR */
+    int32 dst, dstspec;
+    t_addr i, max_returns = MAX_SUB_RETURN_SKIP;
+    int32 save_Regs[8];
+
+    memcpy (save_Regs, R, sizeof(R));       /* save register state */
+    PC = PC + 2;                            /* account for instruction fetch */
+    dstspec = sim_eval[0] & 077;
+    dst = GeteaW (dstspec);
+    if (CPUT (CPUT_05|CPUT_20) &&           /* 11/05, 11/20 */
+        ((dstspec & 070) == 020))           /* JSR (R)+? */
+        dst = R[dstspec & 07];              /* use post incr */
+    memcpy (R, save_Regs, sizeof(R));       /* restore register state */
+    returns[0] = PC + (1 - fprint_sym (stdnul, PC, sim_eval, &cpu_unit, SWMASK ('M')));
+    if (((t_addr)dst > returns[0]) && ((dst - returns[0]) < max_returns*2))
+        max_returns = (dst - returns[0])/2;
+    for (i=1; i<max_returns; i++)
+        returns[i] = returns[i-1] + 2;      /* Possible skip return */
+    returns[i] = 0;                         /* Make sure the address list ends with a zero */
+    *ret_addrs = returns;
+    return TRUE;
+    }
+return FALSE;
+}
+
 /* Boot setup routine */
 
 void cpu_set_boot (int32 pc)