x86: rename stack_pointer to kernel_trap_sp

Choose a less generic name for such a special case.  Add
a comment explaining the odd use in X86_32.

Change the one user of stack_pointer.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/oprofile/backtrace.c

@@ -77,7 +77,7 @@ void
 x86_backtrace(struct pt_regs * const regs, unsigned int depth)
 {
 	struct frame_head *head = (struct frame_head *)frame_pointer(regs);
-	unsigned long stack = stack_pointer(regs);
+	unsigned long stack = kernel_trap_sp(regs);
 
 	if (!user_mode_vm(regs)) {
 		if (depth)

include/asm-x86/ptrace.h

@@ -182,7 +182,13 @@ static inline int v8086_mode(struct pt_regs *regs)
 #endif
 }
 
-static inline unsigned long stack_pointer(struct pt_regs *regs)
+/*
+ * X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode
+ * when it traps.  So regs will be the current sp.
+ *
+ * This is valid only for kernel mode traps.
+ */
+static inline unsigned long kernel_trap_sp(struct pt_regs *regs)
 {
 #ifdef CONFIG_X86_32
 	return (unsigned long)regs;