linux-kernel - Re: [PATCH -next v3] arm64: fix build warning for ARM64_MEMSTART

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Message-ID: <ZMvefmB6unOE+OPB@arm.com>
Date:   Thu, 3 Aug 2023 18:06:06 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Zhang Jianhua <chris.zjh@...wei.com>
Cc:     will@...nel.org, mark.rutland@....com, ryan.roberts@....com,
        joey.gouly@....com, ardb@...nel.org, anshuman.khandual@....com,
        bhe@...hat.com, thunder.leizhen@...wei.com, broonie@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v3] arm64: fix build warning for
 ARM64_MEMSTART_SHIFT

On Tue, Jul 25, 2023 at 08:24:04PM +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
>       |     ^~~~~~~~~~~~~~~~~~~~
> 
> The reason is that PUD_SHIFT isn't defined if CONFIG_PGTABLE_LEVELS == 3
> and CONFIG_VA_BITS == 39.

The correct description is that the generic PUD_SHIFT isn't defined for
asm files, we still have it defined for C files (there's an #ifndef
__ASSEMBLY__ guard).

> Now move the macro ARM64_MEMSTART_SHIFT and
> ARM64_MEMSTART_ALIGN to arch/arm64/mm/init.c where it is used to avoid
> this issue, and also there is no other place to call these two macro.
> 
> Signed-off-by: Zhang Jianhua <chris.zjh@...wei.com>

This fix works for me. I'll leave it to Will for 6.6 as apart from the
warning with W=1, there's no other issue (ARM64_MEMSTART_* are not used
in any asm files).

Reviewed-by: Catalin Marinas <catalin.marinas@....com>