linux-kernel - Re: [PATCH -next v2] arm64: fix build warning for ARM64_MEMSTART

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Message-ID: <9fcfe47f-9289-8eb5-ce4e-9f66648b0e89@huawei.com>
Date:   Tue, 25 Jul 2023 16:47:46 +0800
From:   "zhangjianhua (E)" <chris.zjh@...wei.com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>
CC:     <will@...nel.org>, <ryan.roberts@....com>, <joey.gouly@....com>,
        <ardb@...nel.org>, <mark.rutland@....com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next v2] arm64: fix build warning for
 ARM64_MEMSTART_SHIFT


在 2023/7/25 12:22, Anshuman Khandual 写道:
>
> On 7/24/23 20:41, Catalin Marinas wrote:
>> On Mon, Jul 24, 2023 at 05:27:51PM +0000, Zhang Jianhua wrote:
>>> When building with W=1, the following warning occurs.
>>>
>>> arch/arm64/include/asm/kernel-pgtable.h:129:41: error: "PUD_SHIFT" is not defined, evaluates to 0 [-Werror=undef]
>>>    129 | #define ARM64_MEMSTART_SHIFT            PUD_SHIFT
>>>        |                                         ^~~~~~~~~
>>> arch/arm64/include/asm/kernel-pgtable.h:142:5: note: in expansion of macro ‘ARM64_MEMSTART_SHIFT’
>>>    142 | #if ARM64_MEMSTART_SHIFT < SECTION_SIZE_BITS
>>>        |     ^~~~~~~~~~~~~~~~~~~~
>> Another thing that's missing here is that the warning is probably when
>> this file is included from asm-offests.h or some .S file.
>>
>>> diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
>>> index 577773870b66..51bdce66885d 100644
>>> --- a/arch/arm64/include/asm/kernel-pgtable.h
>>> +++ b/arch/arm64/include/asm/kernel-pgtable.h
>>> @@ -125,12 +125,14 @@
>>>    * (64k granule), or a multiple that can be mapped using contiguous bits
>>>    * in the page tables: 32 * PMD_SIZE (16k granule)
>>>    */
>>> -#if defined(CONFIG_ARM64_4K_PAGES)
>>> +#if defined(CONFIG_ARM64_4K_PAGES) && defined(PUD_SHIFT)
>>>   #define ARM64_MEMSTART_SHIFT		PUD_SHIFT
>> That's not the correct fix since PUD_SHIFT should always be defined.
>> When CONFIG_PGTABLE_LEVELS == 3, pgtable-types.h includes
>> asm-generic/pgtable-nopud.h and this defines PUD_SHIFT. We either got
> Right, PUD_SHIFT is always defined irrespective of page table levels.
>
>> ARM64_MEMSTART_SHIFT defined in the wrong file or kernel-pgtable.h does
>> not pull the relevant headers (either directly or via an included
>> header). Even if kernel-pgtable.h ends up including the nopud/nopmd
>> headers, P*D_SHIFT is guarded by an #indef __ASSEMBLY__ in those files.
>>
>> Something like below appears to fix this, though I'm not particularly
>> fond of guarding the ARM64_MEMSTART_* definitions by #ifndef
>> __ASSEMBLY__ for no apparent reason (could add a comment though):
>>
>> -----------------------8<---------------------------
>> diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
>> index 577773870b66..fcea7e87a6ca 100644
>> --- a/arch/arm64/include/asm/kernel-pgtable.h
>> +++ b/arch/arm64/include/asm/kernel-pgtable.h
>> @@ -118,6 +118,8 @@
>>   #define SWAPPER_RX_MMUFLAGS	(SWAPPER_RW_MMUFLAGS | PTE_RDONLY)
>>   #endif
>>   
>> +#ifndef __ASSEMBLY__
>> +
>>   /*
>>    * To make optimal use of block mappings when laying out the linear
>>    * mapping, round down the base of physical memory to a size that can
>> @@ -145,4 +147,6 @@
>>   #define ARM64_MEMSTART_ALIGN	(1UL << ARM64_MEMSTART_SHIFT)
>>   #endif
>>   
>> +#endif /* __ASSEMBLY__ */
>> +
>>   #endif	/* __ASM_KERNEL_PGTABLE_H */
>> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
>> index e4944d517c99..22b36f2d5d93 100644
>> --- a/arch/arm64/include/asm/pgtable-hwdef.h
>> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
>> @@ -6,6 +6,7 @@
>>   #define __ASM_PGTABLE_HWDEF_H
>>   
>>   #include <asm/memory.h>
>> +#include <asm/pgtable-types.h>
>>   
>>   /*
>>    * Number of page-table levels required to address 'va_bits' wide
>> diff --git a/arch/arm64/include/asm/pgtable-types.h b/arch/arm64/include/asm/pgtable-types.h
>> index b8f158ae2527..ae86e66fdb11 100644
>> --- a/arch/arm64/include/asm/pgtable-types.h
>> +++ b/arch/arm64/include/asm/pgtable-types.h
>> @@ -11,6 +11,8 @@
>>   
>>   #include <asm/types.h>
>>   
>> +#ifndef __ASSEMBLY__
>> +
>>   typedef u64 pteval_t;
>>   typedef u64 pmdval_t;
>>   typedef u64 pudval_t;
>> @@ -44,6 +46,8 @@ typedef struct { pteval_t pgprot; } pgprot_t;
>>   #define pgprot_val(x)	((x).pgprot)
>>   #define __pgprot(x)	((pgprot_t) { (x) } )
>>   
>> +#endif /* __ASSEMBLY__ */
>> +
>>   #if CONFIG_PGTABLE_LEVELS == 2
>>   #include <asm-generic/pgtable-nopmd.h>
>>   #elif CONFIG_PGTABLE_LEVELS == 3
>> -----------------------8<---------------------------
>>
>> To avoid guarding the ARM64_MEMSTART_* definitions, we could instead
>> move the P*D_SHIFT definitions in asm-generic/pgtable-nop*d.h outside
>> the #ifndef __ASSEMBLY__ block.
> OR could ARM64_MEMSTART_SHIFT and ARM64_MEMSTART_ALIGN computation blocks
> be moved inside arch/arm64/mm/init.c, where it is used exclusively. Seems
> to be solving the problem as well.

This method can avoid the current compilation warning, but does not 
solve the problem

that PUD_SHIFT and PMD_SHIFT undefined in fact, and it is contrary to 
XXX_SHIFT should

always be defined. Maybe it would be more appropriate to solve this 
issue directly.