This adds static information about the code regions where the stack
pointer cannot be relied upon. Kernel debuggers may then use this
information to determine which stack to switch to when having a need
to switch off of namely the NMI stack.

From: Jan Beulich <jbeulich@novell.com>

Index: 2.6.14-nlkd/arch/x86_64/ia32/ia32entry.S
===================================================================
--- 2.6.14-nlkd.orig/arch/x86_64/ia32/ia32entry.S	2005-11-09 11:12:58.000000000 +0100
+++ 2.6.14-nlkd/arch/x86_64/ia32/ia32entry.S	2005-11-04 17:18:10.000000000 +0100
@@ -60,6 +60,7 @@ ENTRY(ia32_sysenter_target)
 	CFI_REGISTER	rsp,rbp
 	swapgs
 	movq	%gs:pda_kernelstack, %rsp
+0:	STACK_INVALID ia32_sysenter_target, 0b
 	addq	$(PDA_STACKOFFSET),%rsp	
 	sti	
  	movl	%ebp,%ebp		/* zero extension */
@@ -169,6 +170,7 @@ ENTRY(ia32_cstar_target)
 	movl	%esp,%r8d
 	CFI_REGISTER	rsp,r8
 	movq	%gs:pda_kernelstack,%rsp
+0:	STACK_INVALID ia32_cstar_target, 0b
 	sti
 	SAVE_ARGS 8,1,1
 	movl 	%eax,%eax	/* zero extension */
@@ -211,8 +213,10 @@ cstar_do_call:	
 	/*CFI_REGISTER rflags,r11*/
 	movl RSP-ARGOFFSET(%rsp),%esp
 	CFI_RESTORE rsp
+0:	STACK_INVALID 0b, 1f
 	swapgs
 	sysretl
+1:
 	
 cstar_tracesys:	
 	CFI_RESTORE_STATE
Index: 2.6.14-nlkd/arch/x86_64/kernel/entry.S
===================================================================
--- 2.6.14-nlkd.orig/arch/x86_64/kernel/entry.S	2005-11-09 10:45:26.000000000 +0100
+++ 2.6.14-nlkd/arch/x86_64/kernel/entry.S	2005-11-07 14:56:02.000000000 +0100
@@ -190,6 +190,7 @@ ENTRY(system_call)
 	swapgs
 	movq	%rsp,%gs:pda_oldrsp 
 	movq	%gs:pda_kernelstack,%rsp
+0:	STACK_INVALID system_call, 0b
 	sti					
 	SAVE_ARGS 8,1
 	movq  %rax,ORIG_RAX-ARGOFFSET(%rsp) 
@@ -224,8 +225,10 @@ sysret_check:		
 	RESTORE_ARGS 0,-ARG_SKIP,1
 	/*CFI_REGISTER	rflags,r11*/
 	movq	%gs:pda_oldrsp,%rsp
+0:	STACK_INVALID 0b, 1f
 	swapgs
 	sysretq
+1:
 
 	/* Handle reschedules */
 	/* edx:	work, edi: workmask */	
Index: 2.6.14-nlkd/arch/x86_64/kernel/vmlinux.lds.S
===================================================================
--- 2.6.14-nlkd.orig/arch/x86_64/kernel/vmlinux.lds.S	2005-11-09 11:12:58.000000000 +0100
+++ 2.6.14-nlkd/arch/x86_64/kernel/vmlinux.lds.S	2005-11-04 16:19:33.000000000 +0100
@@ -30,6 +30,13 @@ SECTIONS
 
   _etext = .;			/* End of text section */
 
+#ifdef CONFIG_NLKD
+  . = ALIGN(8);			/* RSP invalid table */
+  __start___stack_invalid = .;
+  __stack_invalid : AT(ADDR(__stack_invalid) - LOAD_OFFSET) { *(__stack_invalid) }
+  __stop___stack_invalid = .;
+#endif
+
   . = ALIGN(16);		/* Exception table */
   __start___ex_table = .;
   __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) { *(__ex_table) }
Index: 2.6.14-nlkd/include/asm-x86_64/calling.h
===================================================================
--- 2.6.14-nlkd.orig/include/asm-x86_64/calling.h	2005-11-09 11:12:58.000000000 +0100
+++ 2.6.14-nlkd/include/asm-x86_64/calling.h	2005-11-07 10:25:38.000000000 +0100
@@ -158,6 +158,17 @@
 	RESTORE_ARGS 0,\addskip
 	.endm
 
+#ifndef MODULE
+	.macro STACK_INVALID from, to
+# ifdef CONFIG_NLKD
+	.section __stack_invalid, "a", @progbits
+	.align 8
+	.quad \from, \to
+	.previous
+# endif
+ 	.endm
+#endif
+
 	.macro icebp
 	.byte 0xf1
 	.endm