Use a more conventional stack arrangement in PXELINUX. Also make itsyslinux-2.00-pre16

possible to query the invocation record for PXELINUX.

4 files changed, 73 insertions, 29 deletions

diff --git a/bootsect.inc b/bootsect.inc
index b114c4eb..ccf5331c 100644
--- a/bootsect.inc
+++ b/bootsect.inc
@@ -86,13 +86,12 @@ load_bootsec:
 		pop ecx			; Byte count to copy
 
 		cli
-%if IS_PXELINUX
-		lss sp,[Stack]		; Reset stack to PXE original
-		pop es
-%else
 		xor ebx,ebx
 		mov ds,bx
 		mov es,bx
+%if IS_PXELINUX
+		lss sp,[InitStack]	; Reset stack to PXE original
+%else
 		mov esp,7C00h
 		pushad
 		pushfd
diff --git a/comboot.doc b/comboot.doc
index f427246f..43c80f99 100644
--- a/comboot.doc
+++ b/comboot.doc
@@ -341,6 +341,7 @@ AX=000Ah	Get Derivative-Specific Information
 	Output:	AL	32h (PXELINUX)
 		DX	PXE API version detected (DH=major, DL=minor)
 		ES:BX	pointer to PXENV+ or !PXE structure
+		FS:SI	pointer to original stack with invocation record
 
 		Note: DX notes the API version detected by PXELINUX,
 		which may be more conservative than the actual version
@@ -354,6 +355,26 @@ AX=000Ah	Get Derivative-Specific Information
 		signature to determine which particular structure was
 		provided.
 
+		The FS:SI pointer points to the top of the original stack
+		provided by the PXE stack, with the following values
+		pushed at the time PXELINUX is started:
+
+		fs:[si+0]	GS		<- top of stack
+		fs:[si+2]	FS
+		fs:[si+4]	ES
+		fs:[si+6]	DS
+		fs:[si+8]	EFLAGS
+		fs:[si+12]	EDI
+		fs:[si+16]	ESI
+		fs:[si+20]	EBP
+		fs:[si+24]	-
+		fs:[si+28]	EBX
+		fs:[si+32]	EDX
+		fs:[si+36]	ECX
+		fs:[si+40]	EAX
+		fs:[si+44]	PXE return IP	<- t.o.s. when PXELINUX invoked
+		fs:[si+46]	PXE return CS
+
 
 	[ISOLINUX]
 	Input:	AX	000Ah
@@ -394,11 +415,13 @@ AX=000Ch	Perform final cleanup
 	INVOKING THIS CALL, NO OTHER API CALLS MAY BE INVOKED, NOR MAY
 	THE PROGRAM TERMINATE AND RETURN TO THE BOOT LOADER.  This
 	call basically tells the boot loader "get out of the way, I'll
-	handle it from here."  The boot loader will continue to
-	provide interrupt and BIOS call thunking services as long its
-	memory areas (0x1000-0xffff, 0x100000-0x100fff) are not
-	overwritten.  MAKE SURE TO DISABLE INTERRUPTS BEFORE
-	OVERWRITING THESE MEMORY AREAS.
+	handle it from here."
+
+	For COM32 images, the boot loader will continue to provide
+	interrupt and BIOS call thunking services as long its memory
+	areas (0x1000-0xffff, 0x100000-0x100fff) are not overwritten.
+	MAKE SURE TO DISABLE INTERRUPTS, AND INSTALL NEW GDT AND IDTS
+	BEFORE OVERWRITING THESE MEMORY AREAS.
 
 	The permissible values for DX are as follows:
 
diff --git a/comboot.inc b/comboot.inc
index 15b25fce..46463694 100644
--- a/comboot.inc
+++ b/comboot.inc
@@ -19,13 +19,15 @@
 
 ; Parameter registers definition; this is the definition
 ; of the stack frame used by INT 21h and INT 22h.
-%define		P_FLAGS		word [bp+40]
-%define		P_FLAGSL	byte [bp+40]
-%define		P_FLAGSH	byte [bp+41]
-%define		P_CS		word [bp+38]
-%define		P_IP		word [bp+36]
-%define		P_DS		word [bp+34]
-%define		P_ES		word [bp+32]
+%define		P_FLAGS		word [bp+44]
+%define		P_FLAGSL	byte [bp+44]
+%define		P_FLAGSH	byte [bp+45]
+%define		P_CS		word [bp+42]
+%define		P_IP		word [bp+40]
+%define		P_DS		word [bp+38]
+%define		P_ES		word [bp+36]
+%define		P_FS		word [bp+34]
+%define		P_GS		word [bp+32]
 %define		P_EAX		dword [bp+28]
 %define		P_AX		word [bp+28]
 %define		P_HAX		word [bp+30]
@@ -147,6 +149,8 @@ comboot_setup_api:
 comboot_int21:	cli
 		push ds
 		push es
+		push fs
+		push gs
 		pushad
 		cld
 		mov bp,cs
@@ -167,6 +171,8 @@ comboot_int21:	cli
 comboot_resume:
 		setc P_FLAGSL		; Propagate CF->error
 		popad
+		pop gs
+		pop fs
 		pop es
 		pop ds
 		iret
@@ -277,6 +283,8 @@ comboot_int22:
 		cli
 		push ds
 		push es
+		push fs
+		push gs
 		pushad
 		cld
 		mov bp,cs
@@ -453,6 +461,10 @@ comapi_derinfo:
 		mov P_BX,ax
 		mov ax,[StrucPtr+2]
 		mov P_ES,ax
+		mov ax,[InitStack]
+		mov P_SI,ax
+		mov ax,[InitStack+2]
+		mov P_FS,ax
 %elif IS_ISOLINUX
 		mov al,[DriveNo]
 		mov P_DL,al
diff --git a/pxelinux.asm b/pxelinux.asm
index 302ed0b3..fd00340e 100644
--- a/pxelinux.asm
+++ b/pxelinux.asm
@@ -194,7 +194,7 @@ RamdiskMax	resd 1			; Highest address for a ramdisk
 KernelSize	resd 1			; Size of kernel (bytes)
 SavedSSSP	resd 1			; Our SS:SP while running a COMBOOT image
 PMESP		resd 1			; Protected-mode ESP
-Stack		resd 1			; Pointer to reset stack
+InitStack	resd 1			; Pointer to reset stack
 PXEEntry	resd 1			; !PXE API entry point
 RebootTime	resd 1			; Reboot timeout, if set by option
 KernelClust	resd 1			; Kernel size in clusters
@@ -271,6 +271,8 @@ packet_buf_size	equ $-packet_buf
 
 		section .text
                 org 7C00h
+StackBuf	equ $
+
 ;
 ; Primary entry point.
 ;
@@ -290,12 +292,19 @@ _start1:
 
 		mov ax,cs
 		mov ds,ax
-		sti			; Stack already set up by PXE
+
+		; That is all pushed onto the PXE stack.  Save the pointer
+		; to it and switch to an internal stack.
+		mov [InitStack],sp
+		mov [InitStack+2],ss
+
+		cli			; Paranoia
+		mov ss,ax
+		mov sp,StackBuf
+
+		sti			; Stack set up and ready
 		cld			; Copy upwards
 
-		push ds
-		mov [Stack],sp
-		mov [Stack+2],ss
 ;
 ; Initialize screen (if we're using one)
 ;
@@ -803,10 +812,6 @@ config_scan:
 %define HAVE_UNLOAD_PREP
 %macro	UNLOAD_PREP 0
 		call unload_pxe
-		cli
-		xor ax,ax
-		mov ss,ax
-		mov sp,7C00h			; Set up a conventional stack
 %endmacro
 
 %include "runkernel.inc"
@@ -828,12 +833,15 @@ config_scan:
 ;
 local_boot:
 		call vgaclearmode
-		lss sp,[cs:Stack]		; Restore stack pointer
-		pop ds				; Restore DS
+		xor si,si
+		mov ds,si			; Restore DI
+		mov ss,si
+		mov sp,StackBuf			; Reset the stack
 		mov [LocalBootType],ax
 		mov si,localboot_msg
 		call writestr
 		; Restore the environment we were called with
+		lss sp,[InitStack]
 		pop gs
 		pop fs
 		pop es
@@ -870,7 +878,8 @@ abort_load:
                 mov ax,cs                       ; Restore CS = DS = ES
                 mov ds,ax
                 mov es,ax
-		lss sp,[Stack]			; Reset the stack
+		mov ss,ax
+		mov sp,StackBuf			; Reset the stack
 		sti
                 call cwritestr                  ; Expects SI -> error msg
 al_ok:          jmp enter_command               ; Return to command prompt
@@ -889,7 +898,8 @@ kaboom:
 		mov ax,cs
 		mov es,ax
 		mov ds,ax
-		lss sp,[Stack]
+		mov ss,ax
+		mov sp,StackBuf
 		sti
 .patch:		mov si,bailmsg
 		call writestr		; Returns with AL = 0