- Change the lookup() function to report success or failure using the carry

flag rather than explicitly halting if a lookup failed.
- Add a loop around the call to lookup() to traverse an array of
  nul-terminated strings for possible paths to the boot loader.  A double
  nul character denotes the end of the list.
- Add a new message to say that the boot failed if all of the path lookups
  for a boot loader file failed.
- Add '/boot/loader' as a second boot path.  If you build an ISO using
  risky options to mkisofs such as -U then the loader will be called
  '/boot/loader' rather than '/BOOT/LOADER;0'.  This allows cdboot to work
  with such risky ISO images.
- Bump version to 1.2 to denote added functionality.

The basic idea as well as some of the code were provided by the submitter,
but I added some extra code to use a loop rather than hard-code just 2
possible paths.

PR:		misc/43543
Submitted by:	kientzle
MFC after:	1 week

sys/boot/i386/cdboot/cdboot.s

@@ -139,10 +139,26 @@ load_vd:	push %eax			# Save %eax
 		jmp error			# Halt
 have_vd:					# Have Primary VD
 #
-# Lookup the loader binary.
+# Try to look up the loader binary using the paths in the loader_paths
+# array.
 #
-		mov $loader_path,%si		# File to lookup
-		call lookup			# Try to find it
+		mov $loader_paths,%si		# Point to start of array
+lookup_path:	push %si			# Save file name pointer
+		call lookup			# Try to find file
+		pop %di				# Restore file name pointer
+		jnc lookup_found		# Found this file
+		xor %al,%al			# Look for next
+		mov $0xffff,%cx			#  path name by
+		repnz				#  scanning for
+		scasb				#  nul char
+		inc %di				# Skip nul
+		mov %di,%si			# Point %si at next path
+		mov (%si),%al			# Get first char of next path
+		or %al,%al			# Is it double nul?
+		jnz lookup_path			# No, try it.
+		mov $msg_failed,%si		# Failed message
+		jmp error			# Halt
+lookup_found:					# Found a loader file
 #
 # Load the binary into the buffer.  Due to real mode addressing limitations
 # we have to read it in in 64k chunks.
@@ -266,7 +282,8 @@ pm_end:		sti				# Turn interrupts back on now
 # Lookup the file in the path at [SI] from the root directory.
 #
 # Trashes: All but BX
-# Returns: BX = pointer to record
+# Returns: CF = 0 (success), BX = pointer to record
+#          CF = 1 (not found)
 #
 lookup:		mov $VD_ROOTDIR+MEM_VOLDESC,%bx	# Root directory record
 		push %si
@@ -286,17 +303,21 @@ lookup_dir:	lodsb				# Get first char of path
 		dec %si				# Undo lodsb side effect
 		call find_file			# Lookup first path item
 		jnc lookup_dir			# Try next component
-		mov $msg_lookupfail,%si		# Not found.
+		mov $msg_lookupfail,%si		# Not found message
+		call putstr
+		stc				# Set carry
+		ret
 		jmp error
 lookup_done:	mov $msg_lookupok,%si		# Success message
 		call putstr
+		clc				# Clear carry
 		ret
 
 #
 # Lookup file at [SI] in directory whose record is at [BX].
 #
 # Trashes: All but returns
-# Returns: CF = 0 (success), BX = pointer to record, SX = next path item
+# Returns: CF = 0 (success), BX = pointer to record, SI = next path item
 #          CF = 1 (not found), SI = preserved
 #
 find_file:	mov DIR_EXTENT(%bx),%eax	# Load extent
@@ -536,7 +557,7 @@ name_len:	.byte 0x0			# Length of current name
 
 twiddle_index:	.byte 0x0
 
-msg_welcome:	.asciz	"CD Loader 1.01\r\n\n"
+msg_welcome:	.asciz	"CD Loader 1.2\r\n\n"
 msg_bootinfo:	.asciz	"Building the boot loader arguments\r\n"
 msg_relocate:	.asciz	"Relocating the loader and the BTX\r\n"
 msg_jump:	.asciz	"Starting the BTX loader\r\n"
@@ -548,6 +569,9 @@ msg_lookup2:	.asciz  "... "
 msg_lookupok:	.asciz  "Found\r\n"
 msg_lookupfail:	.asciz  "File not found\r\n"
 msg_load2big:	.asciz  "File too big\r\n"
-loader_path:	.asciz  "/BOOT/LOADER"
+msg_failed:	.asciz	"Boot failed\r\n"
 twiddle_chars:	.ascii	"|/-\\"
+loader_paths:	.asciz  "/BOOT/LOADER"
+		.asciz	"/boot/loader"
+		.byte 0