isolinux: handle a core file greater than 64K

Handle a core file greater than 64K, and handle the case of a BIOS
which can't handle 64K wraparounds.  The latter is messy with CD-ROMs,
since the standard load address (0x7c00) is not 2K aligned.  We will
have to do something similar for disk-based derivatives when dealing
with 4K sector drives.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/core/isolinux.asm b/core/isolinux.asm
index 2151af2..1d75465 100644 (file)
--- a/core/isolinux.asm
+++ b/core/isolinux.asm
@@ -404,8 +404,8 @@ found_file:
                sub eax,SECTOR_SIZE-3           ; ... minus sector loaded
                shr eax,2                       ; bytes->dwords
                mov [ImageDwords],eax           ; boot file dwords
-               add eax,(2047 >> 2)
-               shr eax,9                       ; dwords->sectors
+               add eax,((SECTOR_SIZE-1) >> 2)
+               shr eax,SECTOR_SHIFT-2          ; dwords->sectors
                mov [ImageSectors],ax           ; boot file sectors
 
                mov eax,[bi_file]               ; Address of code to load
@@ -417,34 +417,52 @@ found_file:
                call crlf
 %endif
 
-               ; Just in case some BIOSes have problems with
-               ; segment wraparound, use the normalized address
-               mov bx,((7C00h+2048) >> 4)
-               mov es,bx
-               xor bx,bx
+               ; Load the rest of the file.  However, just in case there
+               ; are still BIOSes with 64K wraparound problems, we have to
+               ; take some extra precautions.  Since the normal load
+               ; address (7C00h) is *not* 2K-sector-aligned, the safest
+               ; way to deal with this is to load into the xfer_buf_seg
+               ; and then copy the data in place.
+               mov bx,(7C00h+SECTOR_SIZE) >> 4
                mov bp,[ImageSectors]
-%ifdef DEBUG_MESSAGES
-               push ax
-               mov si,size_msg
-               call writemsg
-               mov ax,bp
-               call writehex4
-               call crlf
-               pop ax
-%endif
+
+.more:
+               push bx
+               push bp
+               mov dx,xfer_buf_seg
+               mov es,dx
+               mov fs,dx
+               xor bx,bx
+
+               cmp bp,0x10000 >> SECTOR_SHIFT
+               jbe .ok
+               mov bp,0x10000 >> SECTOR_SHIFT
+.ok:
+               push bp
                call getlinsec
+               pop dx
+               pop bp
+               pop bx
+
+               mov es,bx
+               xor si,si
+               xor di,di
+               mov cx,dx
+               shl cx,SECTOR_SHIFT-2
+               fs rep movsd
+
+               mov cx,dx
+               shl cx,SECTOR_SHIFT-4
+               add bx,cx
+               sub bp,dx
+               jnz .more
 
                push ds
                pop es
 
-%ifdef DEBUG_MESSAGES
-               mov si,loaded_msg
-               call writemsg
-%endif
-
                ; Verify the checksum on the loaded image.
 verify_image:
-               mov si,7C00h+2048
+               mov si,7C00h+SECTOR_SIZE
                mov bx,es
                mov ecx,[ImageDwords]
                mov edi,[FirstSecSum]           ; First sector checksum
@@ -778,7 +796,7 @@ getlinsec_ebios:
                push ss
                pop ds                          ; DS <- SS
                 mov ah,42h                      ; Extended Read
-               int 13h
+               call int13
                pop ds
                popad
                lea sp,[si+16]                  ; Remove DAPA
@@ -803,7 +821,7 @@ getlinsec_ebios:
                pushad                          ; Try resetting the device
                xor ax,ax
                mov dl,[DriveNumber]
-               int 13h
+               call int13
                popad
                loop .retry                     ; CX-- and jump if not zero
 
@@ -879,7 +897,7 @@ getlinsec_cbios:
                mov bp,retry_count
 .retry:
                pushad
-               int 13h
+               call int13
                popad
                jc .error
 .resume:
@@ -1030,8 +1048,6 @@ startup_msg:      db 'Starting up, DL = ', 0
 spec_ok_msg:   db 'Loaded spec packet OK, drive = ', 0
 secsize_msg:   db 'Sector size ', 0
 offset_msg:    db 'Main image LBA = ', 0
-size_msg:      db 'Sectors to load = ', 0
-loaded_msg:    db 'Loaded boot image, verifying...', CR, LF, 0
 verify_msg:    db 'Image checksum verified.', CR, LF, 0
 allread_msg    db 'Main image read, jumping to main code...', CR, LF, 0
 %endif