powerpc: Build kernel with -mcmodel=medium

Finally remove the two level TOC and build with -mcmodel=medium.

Unfortunately we can't build modules with -mcmodel=medium due to
the tricks the kernel module loader plays with percpu data:

# -mcmodel=medium breaks modules because it uses 32bit offsets from
# the TOC pointer to create pointers where possible. Pointers into the
# percpu data area are created by this method.
#
# The kernel module loader relocates the percpu data section from the
# original location (starting with 0xd...) to somewhere in the base
# kernel percpu data space (starting with 0xc...). We need a full
# 64bit relocation for this to work, hence -mcmodel=large.

On older kernels we fall back to the two level TOC (-mminimal-toc)

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 13 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 116f0868695b..1697a25ebe91 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -169,6 +169,7 @@ _GLOBAL(generic_secondary_thread_init)
 
         /* get a valid TOC pointer, wherever we're mapped at */
         bl      .relative_toc
+        tovirt(r2,r2)
 
 #ifdef CONFIG_PPC_BOOK3E
         /* Book3E initialization */
@@ -195,6 +196,7 @@ _GLOBAL(generic_secondary_smp_init)
 
         /* get a valid TOC pointer, wherever we're mapped at */
         bl      .relative_toc
+        tovirt(r2,r2)
 
 #ifdef CONFIG_PPC_BOOK3E
         /* Book3E initialization */
@@ -531,6 +533,7 @@ _GLOBAL(pmac_secondary_start)
 
         /* get TOC pointer (real address) */
         bl      .relative_toc
+        tovirt(r2,r2)
 
         /* Copy some CPU settings from CPU 0 */
         bl      .__restore_cpu_ppc970
@@ -665,6 +668,13 @@ _GLOBAL(enable_64b_mode)
  * This puts the TOC pointer into r2, offset by 0x8000 (as expected
  * by the toolchain).  It computes the correct value for wherever we
  * are running at the moment, using position-independent code.
+ *
+ * Note: The compiler constructs pointers using offsets from the
+ * TOC in -mcmodel=medium mode. After we relocate to 0 but before
+ * the MMU is on we need our TOC to be a virtual address otherwise
+ * these pointers will be real addresses which may get stored and
+ * accessed later with the MMU on. We use tovirt() at the call
+ * sites to handle this.
  */
 _GLOBAL(relative_toc)
         mflr    r0
@@ -681,8 +691,9 @@ p_toc:	.llong	__toc_start + 0x8000 - 0b
  * This is where the main kernel code starts.
  */
 _INIT_STATIC(start_here_multiplatform)
-        /* set up the TOC (real address) */
-        bl      .relative_toc
+        /* set up the TOC */
+        bl      .relative_toc
+        tovirt(r2,r2)
 
         /* Clear out the BSS. It may have been done in prom_init,
          * already but that's irrelevant since prom_init will soon