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, 7 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index 1f8988585054..7cf274a2b334 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -2309,13 +2309,14 @@ static void __init prom_check_initrd(unsigned long r3, unsigned long r4)
 
 unsigned long __init prom_init(unsigned long r3, unsigned long r4,
                                unsigned long pp,
-                               unsigned long r6, unsigned long r7)
+                               unsigned long r6, unsigned long r7,
+                               unsigned long kbase)
 {       
         struct prom_t *_prom;
         unsigned long hdr;
-        unsigned long offset = reloc_offset();
 
 #ifdef CONFIG_PPC32
+        unsigned long offset = reloc_offset();
         reloc_got2(offset);
 #endif
 
@@ -2349,9 +2350,11 @@ unsigned long __init prom_init(unsigned long r3, unsigned long r4,
          */
         RELOC(of_platform) = prom_find_machine_type();
 
+#ifndef CONFIG_RELOCATABLE
         /* Bail if this is a kdump kernel. */
         if (PHYSICAL_START > 0)
                 prom_panic("Error: You can't boot a kdump kernel from OF!\n");
+#endif
 
         /*
          * Check for an initrd
@@ -2371,7 +2374,7 @@ unsigned long __init prom_init(unsigned long r3, unsigned long r4,
          * Copy the CPU hold code
          */
         if (RELOC(of_platform) != PLATFORM_POWERMAC)
-                copy_and_flush(0, KERNELBASE + offset, 0x100, 0);
+                copy_and_flush(0, kbase, 0x100, 0);
 
         /*
          * Do early parsing of command line
@@ -2474,7 +2477,7 @@ unsigned long __init prom_init(unsigned long r3, unsigned long r4,
         reloc_got2(-offset);
 #endif
 
-        __start(hdr, KERNELBASE + offset, 0);
+        __start(hdr, kbase, 0);
 
         return 0;
 }