Name: Make PPC64 Use r14 For Per-Cpu Data
Status: Untested
Version: ppc64
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (authored)

To quote Anton Blanchard <anton@samba.org>:

I just had a look at what a percpu data access looks like on ppc64:

        lhz 0,18(13)            /* smp_processor_id() */
        ld 8,.LC92@toc(2)       /* __per_cpu_offset */
        ld 9,.LC108@toc(2)      /* per_cpu__total_mmio_ffs */
        sldi 0,0,3              /* smp_processor_id() * 8 */
        mr 10,9                 /* gcc sucks */
        ldx 11,8,0              /* __per_cpu_offset[smp_processor_id()] */
        ldx 9,10,11             /* finally, load our per cpu variable */

Reserve r14 for the per-cpu pointer, and try to convince the linker to
do the right thing.

diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal ppc64-2.5-paca-r14/arch/ppc64/Makefile linux-ppc64-2.5/arch/ppc64/Makefile
--- ppc64-2.5-paca-r14/arch/ppc64/Makefile	2004-06-07 12:05:50.000000000 +1000
+++ linux-ppc64-2.5/arch/ppc64/Makefile	2004-07-08 15:10:21.236833494 +1000
@@ -27,7 +27,7 @@ CHECK		:= $(CHECK) -m64 -D__powerpc__=1
 LDFLAGS		:= -m elf64ppc
 LDFLAGS_vmlinux	:= -Bstatic -e $(KERNELLOAD) -Ttext $(KERNELLOAD)
 CFLAGS		+= -msoft-float -pipe -Wno-uninitialized -mminimal-toc \
-		   -mtraceback=none
+		   -mtraceback=none -ffixed-r14
 
 ifeq ($(CONFIG_POWER4_ONLY),y)
 	CFLAGS += $(call check_gcc,-mcpu=power4,)