--- head-2.2.16.S	Fri Jan 15 16:57:25 1999
+++ head.S	Sat Feb 16 19:09:00 2002
@@ -84,8 +84,20 @@
 #ifdef __SMP__
 	orw  %bx,%bx
 	jz  1f				/* Initial CPU cleans BSS */
+
+/*
+ * If Open Firmware is running, leave the eflags register as-is so
+ * Open Firmware's debugger can step through the startup code.
+ * The kernel will run under Open Firmware without this modification,
+ * but the debugger won't work.
+ */
+	movl $CL_BASE_ADDR,%ebp
+	cmpl $0x2057464F, 0x7f0(%ebp)	/* Magic number "OFW " */
+	je 2f
+	
 	pushl $0
 	popfl
+2:	
 	jmp checkCPUtype
 1:
 #endif __SMP__
@@ -104,6 +116,17 @@
  * in 16-bit mode for the "real" operations.
  */
 	call setup_idt
+
+/*
+ * If Open Firmware is running, leave the eflags register as-is so
+ * Open Firmware's debugger can step through the startup code.
+ * The kernel will run under Open Firmware without this modification,
+ * but the debugger won't work.
+ */
+	movl $CL_BASE_ADDR,%ebp
+	cmpl $0x2057464F, 0x7fc(%ebp)	/* Magic number "OFW " */
+	je 1f
+	
 /*
  * Initialize eflags.  Some BIOS's leave bits like NT set.  This would
  * confuse the debugger if this code is traced.
@@ -111,6 +134,8 @@
  */
 	pushl $0
 	popfl
+1:
+
 /*
  * Copy bootup parameters out of the way. First 2kB of
  * _empty_zero_page is for boot parameters, second 2kB
@@ -294,6 +319,32 @@
 	addl $8,%edi
 	dec %ecx
 	jne rp_sidt
+	
+	/*
+	 * If Open Firmware loaded us, incorporate its handlers for
+	 * vectors 1 (debugger) and 3 (breakpoint) into our new trap table.
+	 */
+
+	movl $CL_BASE_ADDR,%ebp
+	cmpl $0x2057464F, 0x7fc(%ebp)	/* Magic number "OFW " */
+	jne 1f
+	
+	movl 0x7f4(%ebp),%ebp			/* IDT address */
+	lea SYMBOL_NAME(idt_table),%edi
+
+	/* Vector 1 - debugger */	
+	movl 8(%ebp),%eax
+	movl %eax,8(%edi)
+	movl 0xc(%ebp),%eax
+	movl %eax,0xc(%edi)
+	
+	/* Vector 3 - breakpoint */	
+	movl 0x18(%ebp),%eax
+	movl %eax,0x18(%edi)
+	movl 0x1c(%ebp),%eax
+	movl %eax,0x1c(%edi)
+1:	
+
 	ret
 
 ENTRY(stack_start)
--- traps-2.2.16.c	Thu Jun  8 07:26:42 2000
+++ traps.c	Sat Feb 16 19:09:00 2002
@@ -682,9 +682,18 @@
 		EISA_bus = 1;
 	set_call_gate(&default_ldt,lcall7);
 	set_trap_gate(0,&divide_error);
-	set_trap_gate(1,&debug);
-	set_trap_gate(2,&nmi);
-	set_system_gate(3,&int3);	/* int3-5 can be called from all */
+
+#define PARAM	((unsigned char *)empty_zero_page)
+#define OFW_SIGNATURE (*(unsigned long *) (PARAM+0x7fc))
+	/* Leave Open Firmware's debugger active if its signature is present */
+	if (OFW_SIGNATURE == 0x2057464F) {  /* Magic number "OFW " */
+		set_trap_gate(2,&nmi);
+	} else {
+		set_trap_gate(1,&debug);
+		set_trap_gate(2,&nmi);
+		set_system_gate(3,&int3);   /* int3-5 can be called from all */
+	}
+
 	set_system_gate(4,&overflow);
 	set_system_gate(5,&bounds);
 	set_trap_gate(6,&invalid_op);