Knut Petersen's hack for Award BIOS bugs

diff --git a/NEWS b/NEWS
index 59f0bcf..2895e7c 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -8,6 +8,8 @@ Changes in 2.10:
          these kinds of images by default.  Patch by Patrick
          LoPresti.
        * Major menu improvement from Murali Ganapathy.
+       * ISOLINUX: Wonderfully sick and brilliant workaround for
+         severe bugs in certain Award BIOSes; from Knut Petersen.
 
 Changes in 2.09:
        * SYSLINUX: Remove residual setuid crap from

diff --git a/isolinux.asm b/isolinux.asm
index 33d2231..aebc6d4 100644 (file)
--- a/isolinux.asm
+++ b/isolinux.asm
@@ -301,7 +301,7 @@ initial_csum:       xor edi,edi
                mov dl,[DriveNo]
                mov si,spec_packet
                int 13h
-               jc spec_query_failed    ; Shouldn't happen (BIOS bug)
+               jc award_hack                   ; changed for BrokenAwardHack
                mov dl,[DriveNo]
                cmp [sp_drive],dl               ; Should contain the drive number
                jne spec_query_failed
@@ -386,11 +386,135 @@ integrity_ok:
 %endif
                jmp all_read                    ; Jump to main code
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Start of BrokenAwardHack --- 10-nov-2002           Knut_Petersen@t-online.de
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;
+;; There is a problem with certain versions of the AWARD BIOS ... 
+;; the boot sector will be loaded and executed correctly, but, because the
+;; int 13 vector points to the wrong code in the BIOS, every attempt to
+;; load the spec packet will fail. We scan for the equivalent of
+;;
+;;     mov     ax,0201h
+;;     mov     bx,7c00h
+;;     mov     cx,0006h
+;;     mov     dx,0180h
+;;     pushf
+;;     call    <direct far>
+;;
+;; and use <direct far> as the new vector for int 13. The code above is
+;; used to load the boot code into ram, and there should be no reason
+;; for anybody to change it now or in the future. There are no opcodes
+;; that use encodings relativ to IP, so scanning is easy. If we find the
+;; code above in the BIOS code we can be pretty sure to run on a machine
+;; with an broken AWARD BIOS ... 
+;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+                                                                            ;;
+%ifdef DEBUG_MESSAGES                                                       ;;
+                                                                            ;;
+award_notice   db      "Trying BrokenAwardHack first ...",CR,LF,0           ;;
+award_not_orig db      "BAH: Original Int 13 vector   : ",0                 ;;
+award_not_new  db      "BAH: Int 13 vector changed to : ",0                 ;;
+award_not_succ db      "BAH: SUCCESS",CR,LF,0                               ;;
+award_not_fail db      "BAH: FAILURE"                                       ;;
+award_not_crlf db      CR,LF,0                                              ;;
+                                                                            ;;
+%endif                                                                      ;;
+                                                                            ;;
+award_oldint13 dd      0                                                    ;;
+award_string   db      0b8h,1,2,0bbh,0,7ch,0b9h,6,0,0bah,80h,1,09ch,09ah    ;;
+                                                                            ;;
+                                               ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+award_hack:    mov     si,spec_err_msg         ; Moved to this place from
+               call    writemsg                ; spec_query_faild
+                                               ;
+%ifdef DEBUG_MESSAGES                          ;
+                                               ;
+               mov     si,award_notice         ; display our plan
+               call    writemsg                ;
+               mov     si,award_not_orig       ; display original int 13
+               call    writemsg                ; vector
+%endif                                         ;
+               mov     eax,[13h*4]             ;
+               mov     [award_oldint13],eax    ;
+                                               ;
+%ifdef DEBUG_MESSAGES                          ;
+                                               ;
+               call    writehex8               ;
+               mov     si,award_not_crlf       ; 
+               call    writestr                ;
+%endif                                         ;
+               push    es                      ; save ES
+               mov     ax,0f000h               ; ES = BIOS Seg
+               mov     es,ax                   ;
+               cld                             ;
+               xor     di,di                   ; start at ES:DI = f000:0
+award_loop:    push    di                      ; save DI
+               mov     si,award_string         ; scan for award_string
+               mov     cx,7                    ; length of award_string = 7dw
+               repz    cmpsw                   ; compare
+               pop     di                      ; restore DI
+               jcxz    award_found             ; jmp if found
+               inc     di                      ; not found, inc di
+               jno     award_loop              ; 
+                                               ;
+award_failed:  pop     es                      ; No, not this way :-((
+award_fail2:                                   ;
+                                               ;
+%ifdef DEBUG_MESSAGES                          ;
+                                               ;
+               mov     si,award_not_fail       ; display failure ...
+               call    writemsg                ;
+%endif                                         ;
+               mov     eax,[award_oldint13]    ; restore the original int
+               or      eax,eax                 ; 13 vector if there is one
+               jz      spec_query_failed       ; and try other workarounds
+               mov     [13h*4],eax             ;
+               jmp     spec_query_failed       ;
+                                               ;
+award_found:   mov     eax,[es:di+0eh]         ; load possible int 13 addr
+               pop     es                      ; restore ES
+                                               ;
+               cmp     eax,[award_oldint13]    ; give up if this is the
+               jz      award_failed            ; active int 13 vector,
+               mov     [13h*4],eax             ; otherwise change 0:13h*4
+                                               ;
+                                               ;
+%ifdef DEBUG_MESSAGES                          ;
+                                               ;
+               push    eax                     ; display message and 
+               mov     si,award_not_new        ; new vector address
+               call    writemsg                ;
+               pop     eax                     ;
+               call    writehex8               ;
+               mov     si,award_not_crlf       ;
+               call    writestr                ;
+%endif                                         ;
+               mov     ax,4B01h                ; try to read the spec packet
+               mov     dl,[DriveNo]            ; now ... it should not fail
+               mov     si,spec_packet          ; any longer
+               int     13h                     ; 
+               jc      award_fail2             ;
+                                               ;
+%ifdef DEBUG_MESSAGES                          ;
+                                               ;
+               mov     si,award_not_succ       ; display our SUCCESS
+               call    writemsg                ;
+%endif                                         ;
+               jmp     found_drive             ; and leave error recovery code
+                                               ;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; End of BrokenAwardHack ----            10-nov-2002 Knut_Petersen@t-online.de
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+
                ; INT 13h, AX=4B01h, DL=<passed in value> failed.
                ; Try to scan the entire 80h-FFh from the end.
+
 spec_query_failed:
-               mov si,spec_err_msg
-               call writemsg
+
+               ; some code moved to BrokenAwardHack
 
                mov dl,0FFh
 .test_loop:    pusha