Fix setregs() on 88110, so that binaries do not skip their first instruction.

Makes binaries beyond init(8) running on MVME197, to some extent.

1 files changed, 21 insertions, 6 deletions

diff --git a/sys/arch/m88k/m88k/m88k_machdep.c b/sys/arch/m88k/m88k/m88k_machdep.c
index 737e888038c..4f276442de9 100644
--- a/sys/arch/m88k/m88k/m88k_machdep.c
+++ b/sys/arch/m88k/m88k/m88k_machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: m88k_machdep.c,v 1.32 2007/11/17 05:36:23 miod Exp $	*/
+/*	$OpenBSD: m88k_machdep.c,v 1.33 2007/11/20 21:47:12 miod Exp $	*/
 /*
  * Copyright (c) 1998, 1999, 2000, 2001 Steve Murphree, Jr.
  * Copyright (c) 1996 Nivas Madhur
@@ -154,18 +154,33 @@ setregs(p, pack, stack, retval)
 
 	/*
 	 * We want to start executing at pack->ep_entry. The way to
-	 * do this is force the processor to fetch from ep_entry. Set
-	 * NIP to something bogus and invalid so that it will be a NOOP.
-	 * And set sfip to ep_entry with valid bit on so that it will be
-	 * fetched.  mc88110 - just set exip to pack->ep_entry.
+	 * do this is force the processor to fetch from ep_entry.
+	 * However, since we will return throug m{88100,88110}_syscall(),
+	 * we need to setup registers so that the success return, when
+	 * ``incrementing'' the instruction pointers, will cause the
+	 * binary to start at the expected address.
 	 */
 #ifdef M88110
 	if (CPU_IS88110) {
-		tf->tf_exip = pack->ep_entry & XIP_ADDR;
+		/*
+		 * Delay slot in exip, so we'll start at enip + 4.
+		 * This relies on the fact that binaries start with
+		 *
+		 *	br.n	1f
+		 *	 first instruction
+		 * 1:	second instruction
+		 *
+		 * So by pretending exip is a delay slot, m88110_syscall()
+		 * will resume at enip + 4... which really is the first
+		 * instruction we want to run.
+		 */
+		tf->tf_exip = (pack->ep_entry & XIP_ADDR) | 1;
+		tf->tf_enip = pack->ep_entry & XIP_ADDR;
 	}
 #endif
 #ifdef M88100
 	if (CPU_IS88100) {
+		/* we'll start at sfip / sfip + 4 */
 		tf->tf_snip = pack->ep_entry & NIP_ADDR;
 		tf->tf_sfip = (pack->ep_entry & FIP_ADDR) | FIP_V;
 	}