--- Net2/arch/i386/boot/boot2.s	2018/04/24 18:12:41	1.1
+++ Net2/arch/i386/boot/boot2.s	2018/04/24 18:20:57	1.1.1.2
@@ -28,13 +28,45 @@
 
 /*
  * HISTORY
- * $Log: boot2.s,v $
- * Revision 1.1  2018/04/24 18:12:41  root
- * Initial revision
+ * boot2.S,v
+Revision 1.3  1993/07/13  21:51:36  mycroft
+Fix addressing bug in bdb junk.
+
+Revision 1.2  1993/07/11  12:02:22  andrew
+Fixes from bde, including support for loading @ any MB boundary (e.g. a
+kernel linked for 0xfe100000 will load at the 1MB mark) and read-ahead
+buffering to speed booting from floppies.  Also works with aha174x
+controllers in enhanced mode.
+
+ *
+ * 93/07/06  bde
+ *	Delete LOADMSG define (not used).
+ *
+ * 93/06/29  bde
+ *	Use EXT.
+ *
+ *	Initialize GDT and IDT pointers at boot time.
+ *
+ *	Convert (drive | head | junk) to drive arg for boot() (not strictly
+ *	necessary - boot() only uses drive & 0x80).
  *
- * Revision 1.1  1993/03/21 18:08:33  cgd
- * after 0.2.2 "stable" patches applied
+ * 93/06/28  bde
+ *	Initialize top bits of %eax for setting _ouraddr.  start.s
+ *	initialized them suitably, but this isn't documented, and the BIOS
+ *	isn't documented to preserve them.
  *
+ *	Use addr32 for setting _ouraddr.  Without this, there were extra bytes
+ *	0, 0 after the store.  These decode as "add %al, (%bx,%si)" in 16-bit
+ *	mode would clobber something (except %al is very likely to be 0 :-).
+ *
+ *	Clear the bss.  This may be unnecessary.  Some is already cleared in
+ *	the disk image.
+ *
+ *	Loop if boot() returns.
+ *
+Revision 1.1  1993/03/21  18:08:33  cgd
+after 0.2.2 "stable" patches applied
+
  * Revision 2.2  92/04/04  11:35:26  rpd
  * 	From 2.5
  * 	[92/03/30            rvb]
@@ -46,34 +78,140 @@
  */
 
 #include	"asm.h"
-#define LOADMSG 1
+
+/* Conventional GDT indexes. */
+#define BOOT_CS_INDEX		3
+#define BOOT_CS16_INDEX		5
+#define BOOT_DS_INDEX		4
+#define DB_CS_INDEX		14
+#define DB_CS16_INDEX		15
+#define DB_DS_INDEX		16
+#define GDT_INDEX		17
+
+/* Vector numbers. */
+#define BREAKPOINT_VECTOR	3
+#define DEBUG_VECTOR		1
+
 /*
  * boot2() -- second stage boot
  */
 
-.globl _ouraddr
+.globl EXT(ouraddr)
 
 ENTRY(boot2)
-	movl	%cs, %ax
-	movl	%ax, %ds
-	movl	%ax, %es
 	data32
-	sall	$4, %eax
+	subl	%eax, %eax
+	mov	%cs, %ax
+	mov	%ax, %ds
+	mov	%ax, %es
 	data32
-	movl	%eax, _ouraddr
-	/* save the drive type and ID */ 
+	shll	$4, %eax
+	addr32
 	data32
-	pushl	%edx
+	movl	%eax, EXT(ouraddr)
+
+	/* fix up GDT entries for bootstrap */
+#define FIXUP(gdt_index) \
+	addr32; \
+	movl	%eax, EXT(Gdt)+(8*gdt_index)+2;	/* actually movw %ax */ \
+	addr32; \
+	movb	%bl, EXT(Gdt)+(8*gdt_index)+4
+
+	data32
+	shld	$16, %eax, %ebx
+	FIXUP(BOOT_CS_INDEX)
+	FIXUP(BOOT_CS16_INDEX)
+	FIXUP(BOOT_DS_INDEX)
+
+	/* fix up GDT entry for GDT, and GDT and IDT pointers */
+	data32
+	movl	%eax, %ecx
+	data32
+	addl	$ EXT(Gdt), %eax
+	data32
+	shld	$16, %eax, %ebx
+	FIXUP(GDT_INDEX)
+	addr32
+	data32
+	movl	%eax, EXT(Gdtr)+2
+	data32
+	addl	$ EXT(Idt), %ecx
+	addr32
+	data32
+	movl	%ecx, EXT(Idtr_prot)+2
+
+	/* %es = vector table segment for a while */
+	push	%es
+	data32
+	subl	%eax, %eax
+	mov	%ax, %es
+
+	/* fix up GDT entries for bdb */
+	data32
+	movl	$4*DEBUG_VECTOR, %esi
+	addr32
+	movl	%es: 2(%esi), %eax	/* actually movw to %ax */
+	data32
+	shll	$4, %eax
+	data32
+	shld	$16, %eax, %ebx
+	FIXUP(DB_CS_INDEX)
+	FIXUP(DB_CS16_INDEX)
+	FIXUP(DB_DS_INDEX)
+
+	/* Fetch entry points of bdb's protected mode trap handlers.  These
+	 * are stored at 2 before the corresponding entry points for real mode.
+	 */
+	data32
+	subl	%ebx, %ebx
+	addr32
+	movl	%es: (%esi), %ebx	/* actually movw to %bx */
+	data32
+	subl	%ecx, %ecx
+	addr32
+	movl	%es: 4*(BREAKPOINT_VECTOR-DEBUG_VECTOR)(%esi), %ecx
+					/* actually movw to %cx */
+
+	/* %es = bdb segment for a while */
+	data32
+	shrl	$4, %eax
+	mov	%ax, %es
+
+	/* fix up IDT entries for bdb */
+	movl	%es: -2(%ebx), %eax	/* actually movw to %ax */
+	addr32
+	movl	%eax, EXT(Idt)+8*DEBUG_VECTOR	/* actually movw %ax */
+	movl	%es: -2(%ecx), %eax	/* actually movw to %ax */
+	addr32
+	movl	%eax, EXT(Idt)+8*BREAKPOINT_VECTOR	/* actually movw %ax */
+
+	/* finished with groping in real mode segments */
+	pop	%es
+
 	/* change to protected mode */
 	data32
-	call	_real_to_prot
+	call	EXT(real_to_prot)
 
-	call	_boot
-	ret
+	/* clear the bss */
+	movl	$ EXT(edata), %edi	/* no EXT(_edata) - krufty ld */
+	movl	$ EXT(end), %ecx	/* or EXT(_end) */
+	subl	%edi, %ecx
+	subb	%al, %al
+	rep
+	stosb
+
+	movzbl	%dl, %edx	/* discard head (%dh) and random high bits */
+	pushl	%edx
+	call	EXT(boot)
+oops:
+	hlt
+	jmp	oops
 
 	.data
         .align 2
+#if 0 /* XXX this would give losing "_ouraddr :".  Better declared in C */
+EXT(ouraddr):
+#else
 _ouraddr:
+#endif
         .long 0
-
-