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, 18 insertions, 1 deletions

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 78c2b024371a..31d8965e0847 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -67,7 +67,24 @@ LDFLAGS_vmlinux-y := -Bstatic
 LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie
 LDFLAGS_vmlinux := $(LDFLAGS_vmlinux-y)
 
-CFLAGS-$(CONFIG_PPC64)  := -mminimal-toc -mtraceback=no -mcall-aixdesc
+ifeq ($(CONFIG_PPC64),y)
+ifeq ($(call cc-option-yn,-mcmodel=medium),y)
+        # -mcmodel=medium breaks modules because it uses 32bit offsets from
+        # the TOC pointer to create pointers where possible. Pointers into the
+        # percpu data area are created by this method.
+        #
+        # The kernel module loader relocates the percpu data section from the
+        # original location (starting with 0xd...) to somewhere in the base
+        # kernel percpu data space (starting with 0xc...). We need a full
+        # 64bit relocation for this to work, hence -mcmodel=large.
+        KBUILD_CFLAGS_MODULE += -mcmodel=large
+else
+        export NO_MINIMAL_TOC := -mno-minimal-toc
+endif
+endif
+
+CFLAGS-$(CONFIG_PPC64)  := -mtraceback=no -mcall-aixdesc
+CFLAGS-$(CONFIG_PPC64)  += $(call cc-option,-mcmodel=medium,-mminimal-toc)
 CFLAGS-$(CONFIG_PPC32)  := -ffixed-r2 -mmultiple
 
 CFLAGS-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=power7,-mtune=power4)