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-rw-r--r--core/pxelinux.asm19
1 files changed, 14 insertions, 5 deletions
diff --git a/core/pxelinux.asm b/core/pxelinux.asm
index ff0f36c8..929ab673 100644
--- a/core/pxelinux.asm
+++ b/core/pxelinux.asm
@@ -255,12 +255,21 @@ _start1:
mov ds,ax
mov es,ax
+%if 0 ; debugging code only... not intended for production use
; Clobber the stack segment, to test for specific pathologies
mov di,STACK_BASE
mov cx,STACK_LEN >> 1
mov ax,0xf4f4
rep stosw
+ ; Clobber the tail of the 64K segment, too
+ extern __bss1_end
+ mov di,__bss1_end
+ sub cx,di ; CX = 0 previously
+ shr cx,1
+ rep stosw
+%endif
+
; That is all pushed onto the PXE stack. Save the pointer
; to it and switch to an internal stack.
mov [InitStack],sp
@@ -2258,11 +2267,11 @@ do_reset_pxe:
TRACER 'F'
;
-; Look to see if we are on an EFI CSM system. Some EFI
-; CSM systems put the BEV stack in low memory, which means
-; a return to the PXE stack will crash the system. However,
-; INT 18h works reliably, so in that case hack the stack and
-; point the "return address" to an INT 18h instruction.
+; Look to see if we are on an EFI CSM system. Some EFI CSM systems
+; (AMI CSM) put the BEV stack in low memory (just below 64K), which
+; means a return to the PXE stack will crash the system. However, INT
+; 18h works reliably, so in that case hack the stack and point the
+; "return address" to an INT 18h instruction.
;
; Hack the stack instead of the much simpler "just invoke INT 18h
; if we want to reset", so that chainloading other NBPs will work.