powerpc: modules: change r2 save/restore offset for ELFv2 ABI.

ELFv2 uses a different stack offset (24 vs 40) to save r2.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

arch/powerpc/kernel/module_64.c

@@ -41,6 +41,12 @@
 #define DEBUGP(fmt , ...)
 #endif
 
+#if defined(_CALL_ELF) && _CALL_ELF == 2
+#define R2_STACK_OFFSET 24
+#else
+#define R2_STACK_OFFSET 40
+#endif
+
 /* Like PPC32, we need little trampolines to do > 24-bit jumps (into
    the kernel itself).  But on PPC64, these need to be used for every
    jump, actually, to reset r2 (TOC+0x8000). */
@@ -64,7 +70,7 @@ static struct ppc64_stub_entry ppc64_stub =
 	0x3d820000,			/* addis   r12,r2, <high> */
 	0x398c0000,			/* addi    r12,r12, <low> */
 	/* Save current r2 value in magic place on the stack. */
-	0xf8410028, /* std     r2,40(r1) */
+	0xf8410000|R2_STACK_OFFSET,	/* std     r2,R2_STACK_OFFSET(r1) */
 	0xe96c0020,			/* ld      r11,32(r12) */
 	0xe84c0028,			/* ld      r2,40(r12) */
 	0x7d6903a6,			/* mtctr   r11 */
@@ -338,7 +344,8 @@ static int restore_r2(u32 *instruction, struct module *me)
 		       me->name, *instruction);
 		return 0;
 	}
-	*instruction = 0xe8410028;	/* ld r2,40(r1) */
+	/* ld r2,R2_STACK_OFFSET(r1) */
+	*instruction = 0xe8410000 | R2_STACK_OFFSET;
 	return 1;
 }