linux-kernel - Re: [PATCH -next] powerpc/book3s64: fix link error with CONFIG_PPC_RADIX

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Date:   Mon, 7 Sep 2020 10:11:01 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Yang Yingliang <yangyingliang@...wei.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] powerpc/book3s64: fix link error with
 CONFIG_PPC_RADIX_MMU=n



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@...wei.com>
>>> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
>>> ---
>>>   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