[prefix] Allow prefix to specify an arbitrary maximum address for relocation

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/core/relocate.c

  */
 __asmcall void relocate ( struct i386_all_regs *ix86 ) {
 	struct memory_map memmap;
-	unsigned long start, end, size, padded_size;
+	unsigned long start, end, size, padded_size, max;
 	unsigned long new_start, new_end;
 	unsigned i;
 
 	      "...need %lx bytes for %d-byte alignment\n",
 	      start, end, padded_size, max_align );
 
+	/* Determine maximum usable address */
+	max = MAX_ADDR;
+	if ( ix86->regs.ebp && ( ix86->regs.ebp < max ) ) {
+		max = ix86->regs.ebp;
+		DBG ( "Limiting relocation to [0,%lx)\n", max );
+	}
+
 	/* Walk through the memory map and find the highest address
 	 * below 4GB that iPXE will fit into.
 	 */
 
 		DBG ( "Considering [%llx,%llx)\n", region->start, region->end);
 		
-		/* Truncate block to MAX_ADDR.  This will be less than
-		 * 4GB, which means that we can get away with using
-		 * just 32-bit arithmetic after this stage.
+		/* Truncate block to maximum address.  This will be
+		 * less than 4GB, which means that we can get away
+		 * with using just 32-bit arithmetic after this stage.
 		 */
-		if ( region->start > MAX_ADDR ) {
-			DBG ( "...starts after MAX_ADDR=%lx\n", MAX_ADDR );
+		if ( region->start > max ) {
+			DBG ( "...starts after max=%lx\n", max );
 			continue;
 		}
 		r_start = region->start;
-		if ( region->end > MAX_ADDR ) {
-			DBG ( "...end truncated to MAX_ADDR=%lx\n", MAX_ADDR );
-			r_end = MAX_ADDR;
+		if ( region->end > max ) {
+			DBG ( "...end truncated to max=%lx\n", max );
+			r_end = max;
 		} else {
 			r_end = region->end;
 		}

src/arch/i386/prefix/exeprefix.S

 	call	alloc_basemem
 	xorl	%esi, %esi
 	movl	$EXE_DECOMPRESS_ADDRESS, %edi
-	clc
+	xorl	%ebp, %ebp
 	call	install_prealloc
 
 	/* Set up real-mode stack */

src/arch/i386/prefix/libprefix.S

 #ifndef KEEP_IT_REAL
 
 	/* Preserve registers */
-	pushfw
 	pushl	%eax
 	pushl	%ebp
 
 	/* Restore registers and return */
 	popl	%ebp
 	popl	%eax
-	popfw
 	ret
 
 #else /* KEEP_IT_REAL */
 	/* Preserve registers */
 	pushl	%esi
 	pushl	%edi
+	pushl	%ebp
 	/* Allocate space for .text16 and .data16 */
 	call	alloc_basemem
 	/* Image source = %cs:0000 */
 	xorl	%esi, %esi
 	/* Image destination = default */
 	xorl	%edi, %edi
-	/* Allow relocation */
-	clc
+	/* Allow arbitrary relocation */
+	xorl	%ebp, %ebp
 	/* Install text and data segments */
 	call	install_prealloc
 	/* Restore registers and return */
+	popl	%ebp
 	popl	%edi
 	popl	%esi
 	ret
  *   %bx  : .data16 segment address
  *   %esi : Image source physical address (or zero for %cs:0000)
  *   %edi : Decompression temporary area physical address (or zero for default)
- *   CF set : Avoid relocating to top of memory
+ *   %ebp : Maximum end address for relocation (or zero for no maximum)
  * Corrupts:
  *   none
  ****************************************************************************
 	pushw	%ds
 	pushw	%es
 	cld			/* Sanity: clear the direction flag asap */
-	pushfw
 
 	/* Set up %ds for (read-only) access to .prefix */
 	pushw	%cs
 	movw	%ax, (init_librm_vector+2)
 	lcall	*init_librm_vector
 
-	/* Skip relocation if CF was set on entry */
-	popfw
-	pushfw
-	jc	skip_relocate
-
 	/* Call relocate() to determine target address for relocation.
 	 * relocate() will return with %esi, %edi and %ecx set up
 	 * ready for the copy to the new location.
 	/* Initialise librm at new location */
 	progress "  init_librm\n"
 	lcall	*init_librm_vector
-skip_relocate:
 #endif
 
 	/* Close access to payload */
 	lcall	*close_payload_vector
 
 	/* Restore registers */
-	popfw
 	popw	%es
 	popw	%ds
 	popal

src/arch/i386/prefix/romprefix.S

 	 * picked up by the initial shell prompt, and we will drop
 	 * into a shell.
 	 */
-	stc			/* Inhibit relocation */
+	movl	$0xa0000, %ebp	/* Inhibit relocation during POST */
 	pushw	%cs
 	call	exec
 2:
  * Called by the PnP BIOS when it wants to boot us.
  */
 bev_entry:
-	clc			/* Allow relocation */
+	xorl	%ebp, %ebp	/* Allow relocation */
 	pushw	%cs
 	call	exec
 	lret
 	/* Leave keypress in buffer and start iPXE.  The keypress will
 	 * cause the usual initial Ctrl-B prompt to be skipped.
 	 */
-	clc			/* Allow relocation */
+	xorl	%ebp, %ebp	/* Allow relocation */
 	pushw	%cs
 	call	exec
 1:	/* Try to call original INT 19 vector */
 	pushw	%cs
 	popw	%ds
 
-	/* Preserve state of CF */
-	lahf
-
 	/* Print message as soon as possible */
 	movw	$prodstr, %si
 	xorw	%di, %di
 
 	/* Store magic word on BIOS stack and remember BIOS %ss:sp */
 	pushl	$STACK_MAGIC
-	movw	%ss, %dx
-	movw	%sp, %bp
+	movw	%ss, %cx
+	movw	%sp, %dx
 
 	/* Obtain a reasonably-sized temporary stack */
 	xorw	%bx, %bx
 	movw	$0x7c00, %sp
 
 	/* Install iPXE */
-	sahf
-	pushfw
 	call	alloc_basemem
-	popfw
 	movl	image_source, %esi
 	movl	decompress_to, %edi
 	call	install_prealloc
 	pushl	$main
 	pushw	%cs
 	call	prot_call
-	popl	%ecx /* discard */
+	popl	%eax /* discard */
 
 	/* Uninstall iPXE */
 	call	uninstall
 
 	/* Restore BIOS stack */
-	movw	%dx, %ss
-	movw	%bp, %sp
+	movw	%cx, %ss
+	movw	%dx, %sp
 
 	/* Check magic word on BIOS stack */
 	popl	%eax

src/arch/i386/prefix/undiloader.S

 	/* Save registers */
 	pushl	%esi
 	pushl	%edi
+	pushl	%ebp
 	pushw	%ds
 	pushw	%es
 	pushw	%bx
 	movw	%es:14(%di), %ax
 	movl	image_source, %esi
 	movl	decompress_to, %edi
-	clc			/* Allow relocation */
+	xorl	%ebp, %ebp		/* Allow relocation */
 	call	install_prealloc
 	popw	%di
 	/* Call UNDI loader C code */
 	popw	%bx
 	popw	%es
 	popw	%ds
+	popl	%ebp
 	popl	%edi
 	popl	%esi
 	lret