linux-kernel - Re: [PATCH -next] arm64: fix -Wundef warning for PUD

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Message-ID: <b09eef83-db27-d716-d8e2-505f37053ecd@huawei.com>
Date:   Mon, 24 Jul 2023 14:35:02 +0800
From:   "zhangjianhua (E)" <chris.zjh@...wei.com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        <catalin.marinas@....com>, <will@...nel.org>, <joey.gouly@....com>,
        <mark.rutland@....com>, <ardb@...nel.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] arm64: fix -Wundef warning for PUD_SHIFT


在 2023/7/24 11:26, Anshuman Khandual 写道:
>
> On 7/24/23 16:00, 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
>>        |     ^~~~~~~~~~~~~~~~~~~~
>>
>> The reason is that PUD_SHIFT isn't defined if CONFIG_PGTABLE_LEVELS ==
>> 3, and at this time PUD_SHIFT is equal to PGDIR_SHIFT, so define it.
> CONFIG_PGTABLE_LEVELS equals 3 only with CONFIG_VA_BITS = 39.
>
>> Fixes: 06e9bf2fd9b3 ("arm64: choose memstart_addr based on minimum sparsemem section alignment")
> This is not a fix, ARM64_MEMSTART_ALIGN would fallback being (1UL << SECTION_SIZE_BITS)
> when PUD_SHIFT is undefined (aka 0) but agreed that it's not clean.
Yes, it wouldn't be wrong in the end.
>> Signed-off-by: Zhang Jianhua <chris.zjh@...wei.com>
>> ---
>> v2:
>> 	Define PUD_SHIFT before use it instead of judgement
>> ---
>> ---
>>   arch/arm64/include/asm/kernel-pgtable.h | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
>> index 577773870b66..996a144e2929 100644
>> --- a/arch/arm64/include/asm/kernel-pgtable.h
>> +++ b/arch/arm64/include/asm/kernel-pgtable.h
>> @@ -59,6 +59,10 @@
>>   #define EARLY_KASLR	(0)
>>   #endif
>>   
>> +#ifndef PUD_SHIFT
>> +#define PUD_SHIFT PGDIR_SHIFT
>> +#endif
> Rather ARM64_MEMSTART_SHIFT block needs to be re-written in a more pgtable levels agnostic
> manner ? OR maybe something like this.
>
> diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
> index 577773870b66..5a83b4b249e8 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
> -#elif defined(CONFIG_ARM64_16K_PAGES)
> +#elif defined(CONFIG_ARM64_16K_PAGES) && defined(CONT_PMD_SHIFT)
>   #define ARM64_MEMSTART_SHIFT           CONT_PMD_SHIFT
> -#else
> +#elif defined(CONFIG_AR64_64K_PAGES) && defined(PMD_SHIFT)
>   #define ARM64_MEMSTART_SHIFT           PMD_SHIFT
> +#else
> +#define ARM64_MEMSTART_SHIFT           PGDIR_SHIFT
>   #endif
>
> The only cases where PUD_SHIFT or PMD_SHIFT (along with CONT_PMD_SHIFT) would not be defined is
> when XXX_SHIFT level itself matches PGDIR_SHIFT.
Thanks for your reply, this modification seems more comprehensive and 
appropriate. I will send v2 patch soon.
>> +
>>   #define SPAN_NR_ENTRIES(vstart, vend, shift) \
>>   	((((vend) - 1) >> (shift)) - ((vstart) >> (shift)) + 1)
>>