Create two easy-to-use entry points in libprefix: install and

install_prealloc.  I *think* these will suffice for all the 16-bit
prefixes.

src/arch/i386/prefix/dskprefix.S

 	.word 0xAA55
 
 start_runtime:
-	/* Install .text16 and .data16 to top of base memory */
-	call	alloc_basemem
-	call	install_basemem
-
-	/* Install .text and .data to 2MB mark */
-	movl	$(2<<20), %edi
-	call	install_highmem
+	call	install
 
 	/* Jump to .text16 segment */
 	pushw	%ax
 	lret
 	.section ".text16", "awx", @progbits
 1:
-	call	init_gdt
 	pushl	$initialise
 	data32 call	prot_call
 	popl	%eax /* discard */

src/arch/i386/prefix/libprefix.S

  * Parameters:
  *   %esi : byte offset within loaded image (must be a multiple of 16)
  *   %es:edi : destination address
- *   %ecx : length to install
+ *   %ecx : length of (decompressed) data
+ *   %edx : total length of block (including any uninitialised data portion)
  * Returns:
  *   none
  * Corrupts:
- *   %esi, %edi, %ecx
+ *   %esi, %edi, %ecx, %edx
  ****************************************************************************
  */
 	.section ".prefix.lib"
 install_block:
 	/* Preserve registers */
 	pushw	%ds
-	pushw	%ax
+	pushw	%eax
 	
 	/* Starting segment => %ds */
 	movw	%cs, %ax
 	movw	%ax, %ds
 	xorl	%esi, %esi
 
+	/* Calculate start and length of uninitialised data portion */
+	leal	(%edi,%ecx), %eax
+	subl	%ecx, %edx
+	
 	/* Do the copy */
 	cld
-	addr32 rep movsb /* or "call decompress16" */
+	rep addr32 movsb /* or "call decompress16" */
+
+	/* Zero remaining space */
+	movl	%eax, %edi
+	movl	%edx, %ecx
+	xorb	%al, %al
+	rep addr32 stosb
 
 	/* Restore registers */
-	popw	%ax
+	popw	%eax
 	popw	%ds
 	ret
 	.size install_block, . - install_block
  */
 	.section ".prefix.lib"
 	.code16
-	.globl alloc_basemem
 alloc_basemem:
 	/* FBMS => %ax as segment address */
 	movw	$0x40, %ax
  */
 	.section ".prefix.lib"
 	.code16
-	.globl install_basemem
 install_basemem:
 	/* Preserve registers */
 	pushw	%es
 	pushl	%esi
 	pushl	%edi
 	pushl	%ecx
+	pushl	%edx
 
 	/* Install .text16 */
 	movw	%ax, %es
 	xorl	%edi, %edi
 	movl	$_text16_load_offset, %esi
 	movl	$_text16_size, %ecx
+	movl	%ecx, %edx
 	call	install_block
 
 	/* Install .data16 */
 	xorl	%edi, %edi	
 	movl	$_data16_load_offset, %esi
 	movl	$_data16_progbits_size, %ecx
+	movl	$_data16_size, %edx
 	call	install_block
 
 	/* Restore registers */
+	popl	%edx
 	popl	%ecx
 	popl	%edi
 	popl	%esi
  * simpler.
  ****************************************************************************
  */
+	
+#ifndef KEEP_IT_REAL
+	
 	.section ".prefix.lib"
 	.align 16
 gdt:
 gdt_end:
 	.equ	gdt_length, gdt_end - gdt
 	.size gdt, . - gdt
+	
+#endif /* KEEP_IT_REAL */
 
 /****************************************************************************
  * set_segment_limits (real-mode near call)
  *   %cx : Segment limit ($REAL_DS or $FLAT_DS)
  ****************************************************************************
  */
+
+#ifndef KEEP_IT_REAL
+	
 	.section ".prefix.lib"
 	.code16
 set_segment_limits:
 	ret
 	.size set_segment_limits, . - set_segment_limits
 	
+#endif /* KEEP_IT_REAL */
+	
 /****************************************************************************
  * install_highmem (real-mode near call)
  *
  *   none
  ****************************************************************************
  */
+
+#ifndef KEEP_IT_REAL
+
 	.section ".prefix.lib"
 	.code16
-	.globl install_highmem
 install_highmem:
 	/* Preserve registers and interrupt status */
 	pushfl
 	pushl	%esi
 	pushl	%edi
 	pushl	%ecx
+	pushl	%edx
 		
 	/* Disable interrupts and flatten real mode */
 	cli
 	/* Install .text and .data to specified address */
 	xorw	%cx, %cx
 	movw	%cx, %es
-	movl	$_text_load_offset, %esi
-	movl	$_text_progbits_size, %ecx
+	movl	$_textdata_load_offset, %esi
+	movl	$_textdata_progbits_size, %ecx
+	movl	$_textdata_size, %edx
 	call	install_block
 
 	/* Unflatten real mode */
 	call	set_segment_limits
 
 	/* Restore registers and interrupt status */
+	popl	%edx
 	popl	%ecx
 	popl	%edi
 	popl	%esi
 	popfl
 	ret
 	.size install_highmem, . - install_highmem
+	
+#endif /* KEEP_IT_REAL */
+	
+/****************************************************************************
+ * install (real-mode near call)
+ * install_prealloc (real-mode near call)
+ *
+ * Install all text and data segments.
+ *
+ * Parameters:
+ *   %ax : .text16 segment address (install_prealloc only)
+ *   %bx : .data16 segment address (install_prealloc only)
+ * Returns:
+ *   %ax : .text16 segment address
+ *   %bx : .data16 segment address
+ *   %edi : .text physical address (if applicable)
+ * Corrupts:
+ *   none
+ ****************************************************************************
+ */
+	.section ".prefix.lib"
+	.code16
+	.globl install
+install:
+	/* Allocate space for .text16 and .data16 */
+	call	alloc_basemem
+	.size install, . - install
+	.globl install_prealloc
+install_prealloc:
+	/* Install .text16 and .data16 */
+	call	install_basemem
+
+#ifndef KEEP_IT_REAL
+	/* Install .text and .data to 2MB mark.  Use 2MB to avoid
+	 * problems with A20.
+	 */
+	movl	$(2<<20), %edi
+	call	install_highmem
+
+	/* Continue executing in .text16 segment */
+	pushw	%cs
+	pushw	$2f
+	pushw	%ax
+	pushw	$1f
+	lret
+	.section ".text16", "awx", @progbits
+1:
+	/* Set up protected-mode GDT, call relocate(), reset GDT */
+	call	init_gdt
+	pushl	$relocate
+	data32 call	prot_call
+	addw	$4, %sp
+	call	init_gdt
+
+	/* Return to executing in .prefix section */
+	lret
+	.section ".prefix.lib"
+2:
+#endif
+	ret
+	.size install_prealloc, . - install_prealloc

src/arch/i386/scripts/i386.lds

      * will default to:
      *
      *   _prefix_link_addr	= 0
-     *   _text_link_addr	= 0
+     *   _textdata_link_addr	= 0
      *   _load_addr		= 0
      *   _max_align		= 16
      * 
      * The 32-bit sections
      */
 
-    _text_link_addr = DEFINED ( _text_link_addr ) ? _text_link_addr : 0;
-    . = _text_link_addr;
+    _textdata_link_addr = ( DEFINED ( _textdata_link_addr ) ?
+			    _textdata_link_addr : 0 );
+    . = _textdata_link_addr;
+    _textdata = .;
+
     _text = .;
 
-    .text : AT ( _text_load_offset + __text ) {
+    .text : AT ( _textdata_load_offset + __text ) {
 	__text = .;
 	*(.text)
 	*(.text.*)
 
     _data = .;
 
-    .rodata : AT ( _text_load_offset + __rodata ) {
+    .rodata : AT ( _textdata_load_offset + __rodata ) {
 	__rodata = .;
 	*(.rodata)
 	*(.rodata.*)
     }
-    .data : AT ( _text_load_offset + __data ) {
+    .data : AT ( _textdata_load_offset + __data ) {
 	__data = .;
 	*(.data)
 	*(.data.*)
 	*(SORT(.tbl.*))		/* Various tables.  See include/tables.h */
-	_etext_progbits = .;
+	_etextdata_progbits = .;
     }
-    .bss : AT ( _text_load_offset + __bss ) {
+    .bss : AT ( _textdata_load_offset + __bss ) {
 	__bss = .;
 	_bss = .;
 	*(.bss)
 	*(COMMON)
 	_ebss = .;
     }
-    .stack : AT ( _text_load_offset + __stack ) {
+    .stack : AT ( _textdata_load_offset + __stack ) {
 	__stack = .;
 	*(.stack)
 	*(.stack.*)
 
     _edata = .;
 
+    _etextdata = .;
+
     _end = .;
 
     /*
     _data16_progbits_size   = _edata16_progbits - _data16;
     .			    = _data16_load_addr + _data16_progbits_size;
 
-    .			   -= _text_link_addr;
-    _text_load_offset	    = ALIGN ( _max_align );
-    _text_load_addr	    = _text_link_addr + _text_load_offset;
-    _text_size		    = _etext - _text;
-    _text_progbits_size	    = _etext_progbits - _text;
-    .			    = _text_load_addr + _text_progbits_size;
+    .			   -= _textdata_link_addr;
+    _textdata_load_offset   = ALIGN ( _max_align );
+    _textdata_load_addr	    = _textdata_link_addr + _textdata_load_offset;
+    _textdata_size	    = _etextdata - _textdata;
+    _textdata_progbits_size = _etextdata_progbits - _textdata;
+    .			    = _textdata_load_addr + _textdata_progbits_size;
 
     .			    = ALIGN ( _max_align );
 
     _assert = ASSERT ( ( . == ALIGN ( _max_align ) ),
 		       "_data16 is badly aligned" );
 
-    . = _text_load_addr - _text_link_addr;
+    . = _textdata_load_addr - _textdata_link_addr;
     _assert = ASSERT ( ( . == ALIGN ( _max_align ) ),
 		       "_text is badly aligned" );
 

src/arch/i386/transitions/librm.S

 	popw	%gs
 	popal
 	popfl
-	ret
+	data32 ret
 
 /****************************************************************************
  * real_call (protected-mode near call, 32-bit virtual return address)