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

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Message-ID: <4938685e-d293-4970-b964-3b9f560d45dd@arm.com>
Date:   Tue, 25 Jul 2023 09:52:18 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Zhang Jianhua <chris.zjh@...wei.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



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.