Preserve ES:DI instead of probing for $PnPsyslinux-3.53-pre5

The $PnP probe has been found to lock up at least one machine for
reasons unknown.  Drop it; instead, burn the extra few bytes in the
bootsector to save away ES:DI for later restore.

8 files changed, 55 insertions, 50 deletions

diff --git a/bootsect.inc b/bootsect.inc
index 78ad12af..00605171 100644
--- a/bootsect.inc
+++ b/bootsect.inc
@@ -142,38 +142,14 @@ replace_bootstrap:
 		; For PXE, ES:BX -> PXENV+, and this would corrupt
 		; that use.
 
-		; Hunt for $PnP header if one exists
-		mov ax,0F000h
-		mov fs,ax
-		xor bx,bx
-.findpnp:
-		cmp dword [fs:bx], "$PnP"
-		jz .foundpnp
-.againpnp:
-		inc bx
-		cmp bx,-21h		; Don't get a segment overflow error!
-		jbe .findpnp
-		jmp .donepnp		; No $PnP header found
-.foundpnp:
-		movzx cx,byte [fs:bx+5]	; Size of $PnP header
-		cmp cl,21h
-		jb .againpnp		; Invalid $PnP header (too short)
-		push bx
-		xor ax,ax
-.checkpnp:
-		add al,byte [fs:bx]
-		inc bx
-		loop .checkpnp
-		pop bx
-		and al,al
-		jnz .findpnp
-
-		; Found a valid $PnP header, point ES:DI to it
-		mov [es:di+8], bx	; New DI
-		mov [es:di+4], fs	; New ES
-%endif
+		; Restore ES:DI -> $PnP (if we were ourselves called
+		; that way...)
+		mov ax,[OrigESDI]
+		mov bx,[OrigESDI+2]
 
-.donepnp:
+		mov [es:di+8],ax	; New DI
+		mov [es:di+4],bx	; New ES
+%endif
 		pop bx			; Copy from...
 		pop ax			; Copy list count
 
diff --git a/com32/include/syslinux/config.h b/com32/include/syslinux/config.h
index d0cb4c26..8b2ed4c9 100644
--- a/com32/include/syslinux/config.h
+++ b/com32/include/syslinux/config.h
@@ -68,6 +68,7 @@ union syslinux_derivative_info {
     uint16_t ax;
     uint16_t cx;
     uint16_t dx;
+    uint16_t _pad;
     const void *esbx;
     const void *fssi;
     const void *gsdi;
@@ -79,13 +80,16 @@ union syslinux_derivative_info {
     uint8_t ch;
     uint8_t drive_number;
     uint8_t dh;
+    uint16_t _pad;
     const void *ptab_ptr;
+    const uint32_t *esdi_ptr;
   } disk;			/* syslinux/extlinux */
   struct {
     uint8_t filesystem;
     uint8_t ah;
     uint16_t cx;
     uint16_t apiver;
+    uint16_t _pad;
     const void *pxenvptr;
     const void *stack;
   } pxe;			/* pxelinux */
@@ -96,7 +100,9 @@ union syslinux_derivative_info {
     uint8_t ch;
     uint8_t drive_number;
     uint8_t dh;
+    uint16_t _pad;
     const void *spec_packet;
+    const uint32_t *esdi_ptr;
   } iso;			/* isolinux */
 };
 
diff --git a/comboot.doc b/comboot.doc
index c8546b25..3c806c3b 100644
--- a/comboot.doc
+++ b/comboot.doc
@@ -367,9 +367,19 @@ AX=000Ah [2.00]	Get Derivative-Specific Information
 		DL	drive number
 		CL	sector size as a power of 2 (9 = 512 bytes) [3.35]
 		ES:BX	pointer to partition table entry (if DL >= 80h)
+		FS:SI	pointer to initial ES:DI value [3.53]
 
 		Note: This function was broken in EXTLINUX 3.00-3.02.
 
+		On boot, ES:DI is supposed to point to the BIOS $PnP
+		structure, although in practice most operating systems
+		will search for it in memory.  However, preserving
+		this while chainloading is probably a good idea.
+
+		Note that FS:SI is a pointer to a memory location
+		containing the original ES:DI value, not the value
+		itself.
+
 
 	[PXELINUX]
 	Input:	AX	000Ah
@@ -417,6 +427,7 @@ AX=000Ah [2.00]	Get Derivative-Specific Information
 		DL	drive number
 		CL	11 (sector size as a power of 2) [3.35]
 		ES:BX	pointer to El Torito spec packet
+		FS:SI	pointer to initial ES:DI value [3.53]
 
 		Note: Some very broken El Torito implementations do
 		not provide the spec packet information.  If so, ES:BX
diff --git a/comboot.inc b/comboot.inc
index 33414bc4..2c1c8826 100644
--- a/comboot.inc
+++ b/comboot.inc
@@ -460,13 +460,7 @@ comapi_pxecall	equ comapi_err			; Not available
 ;
 comapi_derinfo:
 		mov P_AL,my_id
-%if IS_SYSLINUX || IS_MDSLINUX || IS_EXTLINUX
-		mov al,[DriveNumber]
-		mov P_DL,al
-		mov P_ES,cs
-		mov P_BX,PartInfo
-		mov P_CL,SECTOR_SHIFT
-%elif IS_PXELINUX
+%if IS_PXELINUX
 		mov ax,[APIVer]
 		mov P_DX,ax
 		mov ax,[StrucPtr]
@@ -477,12 +471,21 @@ comapi_derinfo:
 		mov P_SI,ax
 		mov ax,[InitStack+2]
 		mov P_FS,ax
-%elif IS_ISOLINUX
+%else
+		; Physical medium...
+
+		mov P_CL,SECTOR_SHIFT
 		mov al,[DriveNumber]
 		mov P_DL,al
+		mov P_FS,cs
+		mov P_SI,OrigESDI
+%if IS_SYSLINUX || IS_MDSLINUX || IS_EXTLINUX
+		mov P_ES,cs
+		mov P_BX,PartInfo
+%elif IS_ISOLINUX
 		mov P_ES,cs
 		mov P_BX,spec_packet
-		mov P_CL,SECTOR_SHIFT
+%endif
 %endif
 		clc
 		ret
diff --git a/extlinux.asm b/extlinux.asm
index 54fda21e..6666f794 100644
--- a/extlinux.asm
+++ b/extlinux.asm
@@ -148,7 +148,8 @@ xbs_vgatmpbuf	equ 2*trackbufsize
 StackBuf	equ $-44-32		; Start the stack here (grow down - 4K)
 PartInfo	equ StackBuf		; Saved partition table entry
 FloppyTable	equ PartInfo+16		; Floppy info table (must follow PartInfo)
-OrigFDCTabPtr	equ StackBuf-4		; The high dword on the stack
+OrigFDCTabPtr	equ StackBuf-8		; The 2nd high dword on the stack
+OrigESDI	equ StackBuf-4		; The high dword on the stack
 
 ;
 ; Primary entry point.  Tempting as though it may be, we can't put the
@@ -217,12 +218,14 @@ start:
 		xor ax,ax
 		mov ss,ax
 		mov sp,StackBuf		; Just below BSS
+		push es			; Save initial ES:DI -> $PnP pointer
+		push di
 		mov es,ax
 ;
 ; DS:SI may contain a partition table entry.  Preserve it for us.
 ;
 		mov cx,8		; Save partition info
-		mov di,sp
+		mov di,PartInfo
 		rep movsw
 
 		mov ds,ax		; Now we can initialize DS...
diff --git a/isolinux.asm b/isolinux.asm
index 4fbb7724..ba7a6a66 100644
--- a/isolinux.asm
+++ b/isolinux.asm
@@ -215,9 +215,10 @@ xbs_vgatmpbuf	equ 2*trackbufsize
 ;; CD-ROM sector (2K) of the file, so the number one priority is actually
 ;; loading the rest.
 ;;
-StackBuf	equ $-44			; 44 bytes needed for
-						; the bootsector chainloading
-						; code!
+StackBuf	equ $-44		; 44 bytes needed for
+					; the bootsector chainloading
+					; code!
+OrigESDI	equ StackBuf-4          ; The high dword on the stack
 
 bootsec		equ $
 
@@ -241,6 +242,8 @@ _start1:	mov [cs:InitStack],sp		; Save initial stack pointer
 		xor ax,ax
 		mov ss,ax
 		mov sp,StackBuf			; Set up stack
+		push es			; Save initial ES:DI -> $PnP pointer
+		push di
 		mov ds,ax
 		mov es,ax
 		mov fs,ax
@@ -828,7 +831,6 @@ crlf_msg	db CR, LF
 null_msg	db 0
 
 		alignb 4, db 0
-StackPtr	dw StackBuf, 0			; SS:SP for stack reset
 MaxTransfer	dw 32				; Max sectors per transfer
 
 rl_checkpt	equ $				; Must be <= 800h
diff --git a/ldlinux.asm b/ldlinux.asm
index 48c9cd0b..ff900435 100644
--- a/ldlinux.asm
+++ b/ldlinux.asm
@@ -154,7 +154,8 @@ xbs_vgatmpbuf	equ 2*trackbufsize
 StackBuf	equ $-44-32		; Start the stack here (grow down - 4K)
 PartInfo	equ StackBuf		; Saved partition table entry
 FloppyTable	equ PartInfo+16		; Floppy info table (must follow PartInfo)
-OrigFDCTabPtr	equ StackBuf-4		; The high dword on the stack
+OrigFDCTabPtr	equ StackBuf-8		; The 2nd high dword on the stack
+OrigESDI	equ StackBuf-4		; The high dword on the stack
 
 ;
 ; Primary entry point.  Tempting as though it may be, we can't put the
@@ -224,12 +225,14 @@ start:
 		xor ax,ax
 		mov ss,ax
 		mov sp,StackBuf		; Just below BSS
+		push es			; Save initial ES:DI -> $PnP pointer
+		push di
 		mov es,ax
 ;
 ; DS:SI may contain a partition table entry.  Preserve it for us.
 ;
 		mov cx,8		; Save partition info
-		mov di,sp
+		mov di,PartInfo
 		rep movsw
 
 		mov ds,ax		; Now we can initialize DS...
diff --git a/stack.inc b/stack.inc
index 0e39b6ea..4b9fbc64 100644
--- a/stack.inc
+++ b/stack.inc
@@ -31,11 +31,12 @@
 		mov es,%1
 %if IS_SYSLINUX || IS_EXTLINUX
                 mov ss,%1                       ; Just in case...
-                mov sp,StackBuf-2*3		; Reset stack
+                mov sp,StackBuf-2*5		; Reset stack
 %elif IS_PXELINUX
 		lss esp,[BaseStack]
 %elif IS_ISOLINUX
-		lss sp,[StackPtr]
+		mov ss,%1
+		mov sp,StackBuf-2*2
 %else
 		NEED TO KNOW HOW TO RESET STACK
 %endif