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Date:   Mon, 24 Jul 2023 16:11:56 +0100
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Zhang Jianhua <chris.zjh@huawei.com>
Cc:     will@kernel.org, ryan.roberts@arm.com, joey.gouly@arm.com,
        anshuman.khandual@arm.com, ardb@kernel.org, mark.rutland@arm.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next v2] arm64: fix build warning for
 ARM64_MEMSTART_SHIFT
Message-ID: <ZL6UvLlyz3MyVfjr@arm.com>
References: <20230724172751.3048501-1-chris.zjh@huawei.com>
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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
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.

-- 
Catalin