ARM: PIE: Add macro for generating PIE resume trampoline

Add a helper that generates a short snippet of code that updates PIE
relocations, loads the stack pointer and calls a C (or asm) function.
The code gets placed into a PIE section.

Signed-off-by: Russ Dill <Russ.Dill@ti.com>

arch/arm/include/asm/suspend.h

@@ -1,7 +1,32 @@
 #ifndef __ASM_ARM_SUSPEND_H
 #define __ASM_ARM_SUSPEND_H
 
+#include <asm/pie.h>
+
 extern void cpu_resume(void);
 extern int cpu_suspend(unsigned long, int (*)(unsigned long));
 
+/**
+ * ARM_PIE_RESUME - generate a PIE trampoline for resume
+ * @proc:	SoC, should match argument used with PIE_OVERLAY_SECTION()
+ * @func:	C or asm function to call at resume
+ * @stack:	stack to use before calling func
+ */
+#define ARM_PIE_RESUME(proc, func, stack)				\
+static void __naked __noreturn __pie(proc) proc##_resume_trampoline2(void) \
+{									\
+	__asm__ __volatile__(						\
+	"	mov	sp, %0\n"					\
+	: : "r"((stack)) : "sp");					\
+									\
+	func();								\
+}									\
+									\
+void __naked __noreturn __pie(proc) proc##_resume_trampoline(void)	\
+{									\
+	pie_relocate_from_pie();					\
+	proc##_resume_trampoline2();					\
+}									\
+EXPORT_PIE_SYMBOL(proc##_resume_trampoline)
+
 #endif