[RFC][PATCH 5/7] x86/speculation: Change __FILL_RETURN_BUFFER to work with objtool

[Peter Zijlstra]

From: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>

Change __FILL_RETURN_BUFFER so that the stack state is deterministically
defined for each iteration and that objtool can have an accurate view
of the stack.

Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200414103618.12657-8-alexandre.chartre@xxxxxxxxxx
---
 arch/x86/include/asm/nospec-branch.h |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -4,6 +4,7 @@
 #define _ASM_X86_NOSPEC_BRANCH_H_
 
 #include <linux/static_key.h>
+#include <linux/frame.h>
 
 #include <asm/alternative.h>
 #include <asm/alternative-asm.h>
@@ -46,12 +47,14 @@
 #define __FILL_RETURN_BUFFER(reg, nr, sp)	\
 	mov	$(nr/2), reg;			\
 771:						\
+	ANNOTATE_INTRA_FUNCTION_CALL		\
 	call	772f;				\
 773:	/* speculation trap */			\
 	pause;					\
 	lfence;					\
 	jmp	773b;				\
 772:						\
+	ANNOTATE_INTRA_FUNCTION_CALL		\
 	call	774f;				\
 775:	/* speculation trap */			\
 	pause;					\
@@ -59,8 +62,8 @@
 	jmp	775b;				\
 774:						\
 	dec	reg;				\
-	jnz	771b;				\
-	add	$(BITS_PER_LONG/8) * nr, sp;
+	add	$(BITS_PER_LONG/8) * 2, sp;	\
+	jnz	771b;
 
 #ifdef __ASSEMBLY__