powerpc: Make the 64-bit kernel as a position-independent executable

This implements CONFIG_RELOCATABLE for 64-bit by making the kernel as
a position-independent executable (PIE) when it is set.  This involves
processing the dynamic relocations in the image in the early stages of
booting, even if the kernel is being run at the address it is linked at,
since the linker does not necessarily fill in words in the image for
which there are dynamic relocations.  (In fact the linker does fill in
such words for 64-bit executables, though not for 32-bit executables,
so in principle we could avoid calling relocate() entirely when we're
running a 64-bit kernel at the linked address.)

The dynamic relocations are processed by a new function relocate(addr),
where the addr parameter is the virtual address where the image will be
run.  In fact we call it twice; once before calling prom_init, and again
when starting the main kernel.  This means that reloc_offset() returns
0 in prom_init (since it has been relocated to the address it is running
at), which necessitated a few adjustments.

This also changes __va and __pa to use an equivalent definition that is
simpler.  With the relocatable kernel, PAGE_OFFSET and MEMORY_START are
constants (for 64-bit) whereas PHYSICAL_START is a variable (and
KERNELBASE ideally should be too, but isn't yet).

With this, relocatable kernels still copy themselves down to physical
address 0 and run there.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 23 insertions, 3 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 6cdfd44..84856be 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -1360,6 +1360,12 @@ _INIT_STATIC(__boot_from_prom)
 	 */
 	rldicr	r1,r1,0,59
 
+#ifdef CONFIG_RELOCATABLE
+	/* Relocate code for where we are now */
+	mr	r3,r26
+	bl	.relocate
+#endif
+
 	/* Restore parameters */
 	mr	r3,r31
 	mr	r4,r30
@@ -1368,11 +1374,19 @@ _INIT_STATIC(__boot_from_prom)
 	mr	r7,r27
 
 	/* Do all of the interaction with OF client interface */
+	mr	r8,r26
 	bl	.prom_init
 	/* We never return */
 	trap
 
 _STATIC(__after_prom_start)
+#ifdef CONFIG_RELOCATABLE
+	/* process relocations for the final address of the kernel */
+	lis	r25,PAGE_OFFSET@highest	/* compute virtual base of kernel */
+	sldi	r25,r25,32
+	mr	r3,r25
+	bl	.relocate
+#endif
 
 /*
  * We need to run with _stext at physical address PHYSICAL_START.
@@ -1381,10 +1395,9 @@ _STATIC(__after_prom_start)
  *
  * Note: This process overwrites the OF exception vectors.
  */
-	LOAD_REG_IMMEDIATE(r3, PHYSICAL_START)	/* target addr */
-	cmpd	r3,r26			/* In some cases the loader may  */
+	li	r3,0			/* target addr */
+	mr.	r4,r26			/* In some cases the loader may  */
 	beq	9f			/* have already put us at zero */
-	mr	r4,r26			/* source address */
 	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 */
@@ -1617,6 +1630,13 @@ _INIT_STATIC(start_here_multiplatform)
 	ori	r6,r6,MSR_RI
 	mtmsrd	r6			/* RI on */
 
+#ifdef CONFIG_RELOCATABLE
+	/* Save the physical address we're running at in kernstart_addr */
+	LOAD_REG_ADDR(r4, kernstart_addr)
+	clrldi	r0,r25,2
+	std	r0,0(r4)
+#endif
+
 	/* The following gets the stack set up with the regs */
 	/* pointing to the real addr of the kernel stack.  This is   */
 	/* all done to support the C function call below which sets  */