Fix stack-switching mode (USE_PXE_PROVIDED_STACK == 0)

diff --git a/pxelinux.asm b/pxelinux.asm
index a83afd0..0af25a3 100644 (file)
--- a/pxelinux.asm
+++ b/pxelinux.asm
@@ -198,7 +198,8 @@ ConfigName  resb 256-4              ; Configuration file from DHCP option
 PathPrefix     resb 256                ; Path prefix derived from boot file
 DotQuadBuf     resb 16                 ; Buffer for dotted-quad IP address
 IPOption       resb 80                 ; ip= option buffer
-InitStack      resd 1                  ; Pointer to reset stack
+InitStack      resd 1                  ; Pointer to reset stack (SS:SP)
+PXEStack       resd 1                  ; Saved stack during PXE call
 
 ; Warning here: RBFG build 22 randomly overwrites memory location
 ; [0x5680,0x576c), possibly more.  It seems that it gets confused and
@@ -1549,11 +1550,21 @@ unmangle_name:
 ;
 ; This is the main PXENV+/!PXE entry point, using the PXENV+
 ; calling convention.  This is a separate local routine so
-; we can hook special things from it if necessary.
+; we can hook special things from it if necessary.  In particular,
+; some PXE stacks seem to not like being invoked from anything but
+; the initial stack, so humour it.
 ;
 
 pxenv:
+%if USE_PXE_PROVIDED_STACK == 0
+               mov [cs:PXEStack],sp
+               mov [cs:PXEStack+2],ss
+               lss sp,[cs:InitStack]
+%endif
 .jump:         call 0:pxe_thunk                ; Default to calling the thunk
+%if USE_PXE_PROVIDED_STACK == 0
+               lss sp,[cs:PXEStack]
+%endif
                cld                             ; Make sure DF <- 0
                ret
 
@@ -2512,7 +2523,8 @@ pxe_udp_read_pkt:
 ; Misc initialized (data) variables
 ;
                alignb 4, db 0
-BaseStack      dd StackBuf             ; SS:ESP of base stack
+BaseStack      dd StackBuf             ; ESP of base stack
+               dw 0                    ; SS of base stack
 NextSocket     dw 49152                ; Counter for allocating socket numbers
 KeepPXE                db 0                    ; Should PXE be kept around?