powerpc/64: don't refer nr_cpu_ids in asm code when it's undefined

generic_secondary_common_init() calls LOAD_REG_ADDR(r7, nr_cpu_ids)
conditionally on CONFIG_SMP. However, if 'NR_CPUS == 1', kernel doesn't
use the nr_cpu_ids, and in C code, it's just:
  #if NR_CPUS == 1
  #define nr_cpu_ids
  ...

This series makes declaration of nr_cpu_ids conditional on NR_CPUS == 1,
and that reveals the issue, because compiler can't link the
LOAD_REG_ADDR(r7, nr_cpu_ids) against nonexisting symbol.

Current code looks unsafe for those who build kernel with CONFIG_SMP=y and
NR_CPUS == 1. This is weird configuration, but not disallowed.

Fix the linker error by replacing LOAD_REG_ADDR() with LOAD_REG_IMMEDIATE()
conditionally on NR_CPUS == 1.

As the following patch adds CONFIG_FORCE_NR_CPUS option that has the
similar effect on nr_cpu_ids, make the generic_secondary_common_init()
conditional on it too.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Yury Norov <yury.norov@gmail.com>

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index cf2c08902c0569da7c075c6ef386088b98d14125..d36939029701cd886dc4bf80a28e555d4739c65d 100644 (file)
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -400,8 +400,12 @@ generic_secondary_common_init:
 #else
        LOAD_REG_ADDR(r8, paca_ptrs)    /* Load paca_ptrs pointe         */
        ld      r8,0(r8)                /* Get base vaddr of array       */
+#if (NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS)
+       LOAD_REG_IMMEDIATE(r7, NR_CPUS)
+#else
        LOAD_REG_ADDR(r7, nr_cpu_ids)   /* Load nr_cpu_ids address       */
        lwz     r7,0(r7)                /* also the max paca allocated   */
+#endif
        li      r5,0                    /* logical cpu id                */
 1:
        sldi    r9,r5,3                 /* get paca_ptrs[] index from cpu id */