[PATCH 5/5] powerpc: Run relocatable kernel where it's loaded

[Paul Mackerras]

This demonstrates that the relocatable kernel doesn't have to run at
real address 0.  It only copies the interrupt vectors down and leaves
the rest of the kernel where it was loaded, and runs it there.

This is mostly just a proof of concept, since it doesn't do anything
to ensure that the kernel base address is 16kB-aligned, and we
probably want to move the kernel down to 0 in most cases (except for
kdump kernels) anyway.

Signed-off-by: Paul Mackerras <paulus at samba.org>
---
diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index abb3bfe..fdb8565 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -1377,6 +1377,7 @@ _STATIC(__after_prom_start)
 	/* process relocations for the final address of the kernel */
 	lis	r25,PAGE_OFFSET at highest	/* compute virtual base of kernel */
 	sldi	r25,r25,32
+	add	r25,r25,r26
 	mr	r3,r25
 	bl	.relocate
 #endif
@@ -1391,10 +1392,13 @@ _STATIC(__after_prom_start)
 	li	r3,0			/* target addr */
 	mr.	r4,r26			/* In some cases the loader may  */
 	beq	9f			/* have already put us at zero */
-	lis	r5,(copy_to_here - _stext)@ha
-	addi	r5,r5,(copy_to_here - _stext)@l /* # bytes of memory to copy */
 	li	r6,0x100		/* Start offset, the first 0x100 */
 					/* bytes were copied earlier.	 */
+#ifdef CONFIG_RELOCATABLE
+	li	r5,__end_interrupts - _stext	/* just copy interrupts */
+#else
+	lis	r5,(copy_to_here - _stext)@ha
+	addi	r5,r5,(copy_to_here - _stext)@l /* # bytes of memory to copy */
 
 	bl	.copy_and_flush		/* copy the first n bytes	 */
 					/* this includes the code being	 */
@@ -1404,15 +1408,16 @@ _STATIC(__after_prom_start)
 	mtctr	r8
 	bctr
 
+p_end:	.llong	_end - _stext
+
 4:	/* Now copy the rest of the kernel up to _end */
 	addis	r5,r26,(p_end - _stext)@ha
 	ld	r5,(p_end - _stext)@l(r5)	/* get _end */
+#endif
 	bl	.copy_and_flush		/* copy the rest */
 
 9:	b	.start_here_multiplatform
 
-p_end:	.llong	_end - _stext
-
 /*
  * Copy routine used to copy the kernel to start at physical address 0
  * and flush and invalidate the caches as needed.