Try to deal with funny PXE stack problems...

diff --git a/NEWS b/NEWS
index 1864dcd..733987d 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,7 @@ them.
 
 Changes in 2.03:
        * Actually support comment lines in the configuration file.
+       * PXELINUX: Try to resolve some problems with stack switches.
 
 Changes in 2.02:
        * SYSLINUX: Security flaws have been found in the SYSLINUX

diff --git a/comboot.doc b/comboot.doc
index 6236fe8..c66a179 100644 (file)
--- a/comboot.doc
+++ b/comboot.doc
@@ -366,15 +366,15 @@ AX=000Ah  Get Derivative-Specific Information
                [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+8]       EDI
+               [fs:si+12]      ESI
+               [fs:si+16]      EBP
+               [fs:si+20]      -
+               [fs:si+24]      EBX
+               [fs:si+28]      EDX
+               [fs:si+32]      ECX
+               [fs:si+36]      EAX
+               [fs:si+40]      EFLAGS
                [fs:si+44]      PXE return IP   <- t.o.s. when PXELINUX invoked
                [fs:si+46]      PXE return CS
 

diff --git a/pxelinux.asm b/pxelinux.asm
index d4153e7..793134e 100644 (file)
--- a/pxelinux.asm
+++ b/pxelinux.asm
@@ -42,6 +42,7 @@ PKT_RETRY     equ 6                   ; Packet transmit retry count
 PKT_TIMEOUT    equ 12                  ; Initial timeout, timer ticks @ 55 ms
 TFTP_BLOCKSIZE_LG2 equ 9               ; log2(bytes/block)
 TFTP_BLOCKSIZE equ (1 << TFTP_BLOCKSIZE_LG2)
+%assign USE_PXE_PROVIDED_STACK 1       ; Use stack provided by PXE?
 
 ;
 ; TFTP operation codes
@@ -271,7 +272,7 @@ packet_buf_size     equ $-packet_buf
 
                section .text
                 org 7C00h
-StackBuf       equ $
+StackBuf       equ $                   ; Base of stack if we use our own
 
 ;
 ; Primary entry point.
@@ -280,8 +281,8 @@ bootsec             equ $
 _start:
                jmp 0:_start1           ; Canonicalize address
 _start1:
-               pushad                  ; Paranoia... in case of return to PXE
-               pushfd                  ; ... save as much state as possible
+               pushfd                  ; Paranoia... in case of return to PXE
+               pushad                  ; ... save as much state as possible
                push ds
                push es
                push fs
@@ -298,9 +299,15 @@ _start1:
                mov [InitStack],sp
                mov [InitStack+2],ss
 
+%if USE_PXE_PROVIDED_STACK
+               ; Apparently some platforms go bonkers if we
+               ; set up our own stack...
+               mov [BaseStack],sp
+               mov [BaseStack+4],ss
+%endif
+
                cli                     ; Paranoia
-               mov ss,ax
-               mov sp,StackBuf
+               lss esp,[BaseStack]
 
                sti                     ; Stack set up and ready
                cld                     ; Copy upwards
@@ -834,8 +841,7 @@ config_scan:
 local_boot:
                mov si,cs
                mov ds,si                       ; Restore DI
-               mov ss,si
-               mov esp,StackBuf                ; Reset the stack
+               lss esp,[BaseStack]
                mov [LocalBootType],ax
                call vgaclearmode
                mov si,localboot_msg
@@ -846,9 +852,9 @@ local_boot:
                pop fs
                pop es
                pop ds
-               popfd
                popad
                mov ax,[cs:LocalBootType]
+               popfd
                retf                            ; Return to PXE
 
 ;
@@ -878,8 +884,7 @@ abort_load:
                 mov ax,cs                       ; Restore CS = DS = ES
                 mov ds,ax
                 mov es,ax
-               mov ss,ax
-               mov sp,StackBuf                 ; Reset the stack
+               lss esp,[BaseStack]
                sti
                 call cwritestr                  ; Expects SI -> error msg
 al_ok:          jmp enter_command               ; Return to command prompt
@@ -898,8 +903,7 @@ kaboom:
                mov ax,cs
                mov es,ax
                mov ds,ax
-               mov ss,ax
-               mov sp,StackBuf
+               lss esp,[BaseStack]
                sti
 .patch:                mov si,bailmsg
                call writestr           ; Returns with AL = 0
@@ -1654,12 +1658,32 @@ unload_pxe:
                jmp .call_loop
 
 .call_done:
-               mov bx,0FF00h
+%if USE_PXE_PROVIDED_STACK
+               ; We need to switch to our local stack here...
+               pusha
+               pushf
+
+               mov si,sp
+               mov cx,[InitStack]
+               mov di,StackBuf
+               mov [BaseStack],di
+               mov [BaseStack+4],es
+               sub cx,si
+               sub di,cx
+               mov dx,cx                       ; New SP
+               ss rep movsb
+
+               cli
+               mov ss,cx                       ; CX == 0 here
+               mov sp,dx
+               
+               popf
+               popa
+%endif
 
                mov dx,[RealBaseMem]
                cmp dx,[BIOS_fbm]               ; Sanity check
                jna .cant_free
-               inc bx
 
                ; Check that PXE actually unhooked the INT 1Ah chain
                movzx eax,word [4*0x1a]
@@ -1671,7 +1695,6 @@ unload_pxe:
                jae .ok
                cmp ax,[BIOS_fbm]
                jae .cant_free
-               ; inc bx
 
 .ok:
                mov [BIOS_fbm],dx
@@ -2133,6 +2156,9 @@ pxe_udp_read_pkt:
 ;
 ; Misc initialized (data) variables
 ;
+               alignb 4, db 0
+BaseStack      dd StackBuf             ; SS:ESP of base stack
+               dw 0
 AppendLen       dw 0                    ; Bytes in append= command
 KbdTimeOut      dw 0                    ; Keyboard timeout (if any)
 CmdLinePtr     dw cmd_line_here        ; Command line advancing pointer