Re: [PATCH -next] powerpc/book3s64: fix link error with CONFIG_PPC_RADIX_MMU=n

From: Christophe Leroy
Date: Mon Sep 07 2020 - 04:12:06 EST



Le 07/09/2020 à 03:51, Yang Yingliang a écrit :

On 2020/9/6 14:50, Christophe Leroy wrote:


Le 05/09/2020 à 13:25, Yang Yingliang a écrit :
Fix link error when CONFIG_PPC_RADIX_MMU is disabled:
powerpc64-linux-gnu-ld: arch/powerpc/platforms/pseries/lpar.o:(.toc+0x0): undefined reference to `mmu_pid_bits'

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
---
  arch/powerpc/mm/book3s64/mmu_context.c | 4 ++++

In your commit log, you are just mentionning arch/powerpc/platforms/pseries/lpar.o, which is right.

You shouldn't need to modify arch/powerpc/mm/book3s64/mmu_context.c at all, see below.

  arch/powerpc/platforms/pseries/lpar.c  | 2 ++
  2 files changed, 6 insertions(+)

diff --git a/arch/powerpc/mm/book3s64/mmu_context.c b/arch/powerpc/mm/book3s64/mmu_context.c
index 0ba30b8b935b..a8e292cd88f0 100644
--- a/arch/powerpc/mm/book3s64/mmu_context.c
+++ b/arch/powerpc/mm/book3s64/mmu_context.c
@@ -152,6 +152,7 @@ void hash__setup_new_exec(void)
    static int radix__init_new_context(struct mm_struct *mm)
  {
+#ifdef CONFIG_PPC_RADIX_MMU

This shouldn't be required. radix__init_new_context() is only called when radix_enabled() returns true.
As it is a static function, when it is not called it gets optimised away, so you will never get an undefined reference to `mmu_pid_bits` there.
powerpc64-linux-gnu-ld: arch/powerpc/mm/book3s64/mmu_context.o:(.toc+0x0): undefined reference to `mmu_pid_bits'
powerpc64-linux-gnu-ld: arch/powerpc/mm/book3s64/mmu_context.o:(.toc+0x8): undefined reference to `mmu_base_pid'


mmu_context.c is always compiled, it uses mmu_pid_bits and mmu_base_pid.

Yes, mmu_context.c is always compiled, but as I explained, radix__init_new_context() is defined as 'static' so it is optimised out when radix_enabled() returns false because there is no caller in that case.

I just made the test with ppc64_defconfig + CONFIG_PPC_RADIX_MMU=n (GCC 8.1)

The only failure I got was on lpar.c, which I fixed by enclosing the entire radix_init_pseries() in an #ifdef.

Once this is fixed, the build is OK, without any modification to mmu_context.c

powerpc64-linux-objdump -x arch/powerpc/mm/book3s64/mmu_context.o shows only the following objects in the .toc:

RELOCATION RECORDS FOR [.toc]:
OFFSET TYPE VALUE
0000000000000000 R_PPC64_ADDR64 kmalloc_caches
0000000000000008 R_PPC64_ADDR64 vmemmap
0000000000000010 R_PPC64_ADDR64 __pmd_frag_nr
0000000000000018 R_PPC64_ADDR64 __pmd_frag_size_shift

mmu_pid_bits and mmu_base_pid are not part of the undefined objetcs:

0000000000000000 *UND* 0000000000000000 vmemmap
0000000000000000 *UND* 0000000000000000 .mm_iommu_init
0000000000000000 *UND* 0000000000000000 __pmd_frag_nr
0000000000000000 *UND* 0000000000000000 .ida_alloc_range
0000000000000000 *UND* 0000000000000000 .slb_setup_new_exec
0000000000000000 *UND* 0000000000000000 mmu_feature_keys
0000000000000000 *UND* 0000000000000000 .memset
0000000000000000 *UND* 0000000000000000 .memcpy
0000000000000000 *UND* 0000000000000000 .slice_init_new_context_exec
0000000000000000 *UND* 0000000000000000 ._mcount
0000000000000000 *UND* 0000000000000000 .__free_pages
0000000000000000 *UND* 0000000000000000 __pmd_frag_size_shift
0000000000000000 *UND* 0000000000000000 .slice_setup_new_exec
0000000000000000 *UND* 0000000000000000 .ida_free
0000000000000000 *UND* 0000000000000000 .pte_frag_destroy
0000000000000000 *UND* 0000000000000000 .kfree
0000000000000000 *UND* 0000000000000000 .pkey_mm_init
0000000000000000 *UND* 0000000000000000 .kmem_cache_alloc_trace
0000000000000000 *UND* 0000000000000000 .__warn_printk
0000000000000000 *UND* 0000000000000000 _mcount
0000000000000000 *UND* 0000000000000000 kmalloc_caches

Christophe