|author||H. Peter Anvin <firstname.lastname@example.org>||2010-02-12 17:02:50 -0800|
|committer||H. Peter Anvin <email@example.com>||2010-02-12 17:02:50 -0800|
pxelinux: complete but disable debugging code, not for productionsyslinux-3.85-pre10
Disable some debugging code that was never intended for production use. The intent is to track down specific memory-clobbering bugs. Signed-off-by: H. Peter Anvin <firstname.lastname@example.org>
1 files changed, 14 insertions, 5 deletions
diff --git a/core/pxelinux.asm b/core/pxelinux.asm
index ff0f36c8..929ab673 100644
@@ -255,12 +255,21 @@ _start1:
+%if 0 ; debugging code only... not intended for production use
; Clobber the stack segment, to test for specific pathologies
mov cx,STACK_LEN >> 1
+ ; 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
; That is all pushed onto the PXE stack. Save the pointer
; to it and switch to an internal stack.
@@ -2258,11 +2267,11 @@ do_reset_pxe:
-; 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.