powerpc/64: Add an option to force run-at-load to test relocation

This adds a config option that can help exercise the case when
the kernel is not running at PAGE_OFFSET.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Kconfig

@@ -479,6 +479,15 @@ config RELOCATABLE
 	  setting can still be useful to bootwrappers that need to know the
 	  load address of the kernel (eg. u-boot/mkimage).
 
+config RELOCATABLE_TEST
+	bool "Test relocatable kernel"
+	depends on (PPC64 && RELOCATABLE)
+	default n
+	help
+	  This runs the relocatable kernel at the address it was initially
+	  loaded at, which tends to be non-zero and therefore test the
+	  relocation code.
+
 config CRASH_DUMP
 	bool "Build a kdump crash kernel"
 	depends on PPC64 || 6xx || FSL_BOOKE || (44x && !SMP)

arch/powerpc/kernel/head_64.S

@@ -107,12 +107,19 @@ __secondary_hold_acknowledge:
 	 * crash_kernel region.  The loader is responsible for
 	 * observing the alignment requirement.
 	 */
+
+#ifdef CONFIG_RELOCATABLE_TEST
+#define RUN_AT_LOAD_DEFAULT 1		/* Test relocation, do not copy to 0 */
+#else
+#define RUN_AT_LOAD_DEFAULT 0x72756e30  /* "run0" -- relocate to 0 by default */
+#endif
+
 	/* Do not move this variable as kexec-tools knows about it. */
 	. = 0x5c
 	.globl	__run_at_load
 __run_at_load:
 DEFINE_FIXED_SYMBOL(__run_at_load)
-	.long	0x72756e30	/* "run0" -- relocate to 0 by default */
+	.long	RUN_AT_LOAD_DEFAULT
 #endif
 
 	. = 0x60