powerpc: Make load_hander handle upto 64k offset

If we change load_hander() to use an ori instead of addi, we can load handlers
upto 64k away provided we are still 64k aligned.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/exception-64s.h

@@ -55,7 +55,8 @@
  * word.
  */
 #define LOAD_HANDLER(reg, label)					\
-	addi	reg,reg,(label)-_stext;	/* virt addr of handler ... */
+	/* Handlers must be within 64K of kbase, which must be 64k aligned */ \
+	ori	reg,reg,(label)-_stext;	/* virt addr of handler ... */
 
 /* Exception register prefixes */
 #define EXC_HV	H

arch/powerpc/kernel/exceptions-64s.S

@@ -585,8 +585,8 @@ __end_interrupts:
  * Code from here down to __end_handlers is invoked from the
  * exception prologs above.  Because the prologs assemble the
  * addresses of these handlers using the LOAD_HANDLER macro,
- * which uses an addi instruction, these handlers must be in
- * the first 32k of the kernel image.
+ * which uses an ori instruction, these handlers must be in
+ * the first 64k of the kernel image.
  */
 
 /*** Common interrupt handlers ***/

arch/powerpc/kernel/setup_64.c

@@ -601,6 +601,11 @@ void __init setup_arch(char **cmdline_p)
 
 	kvm_linear_init();
 
+	/* Interrupt code needs to be 64K-aligned */
+	if ((unsigned long)_stext & 0xffff)
+		panic("Kernelbase not 64K-aligned (0x%lx)!\n",
+		      (unsigned long)_stext);
+
 	ppc64_boot_msg(0x15, "Setup Done");
 }