On Thu, Mar 06, 2025 at 11:00:16PM +0100, Ingo Molnar wrote:
> * Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
> > Separating out the assembler-compatible defines from the types
> > headers appears to be a bigger patch, since it's all mixed in with C
> > syntax:
> >
> > <=-----------------------------------===============================
> > typedef struct { pud_t pud; } pmd_t;
> >
> > #define PMD_SHIFT PUD_SHIFT
> > #define PTRS_PER_PMD 1
> > #define PMD_SIZE (1UL << PMD_SHIFT)
> > #define PMD_MASK (~(PMD_SIZE-1))
> >
> > /*
> > * The "pud_xxx()" functions here are trivial for a folded two-level
> > * setup: the pmd is never bad, and a pmd always exists (as it's folded
> > * into the pud entry)
> > */
> > static inline int pud_none(pud_t pud) { return 0; }
> > static inline int pud_bad(pud_t pud) { return 0; }
> > static inline int pud_present(pud_t pud) { return 1; }
> > ================================================================>
> >
> > In any case I've removed the commit for the time being until this all
> > is cleared up.
>
> So there's a simple solution: define it on i386 too, via the patch
> below. It appears the double-definition doesn't create any warnings, on
> GCC at least.
Fine by me as long as it gets fixed. Currently it prevents the WERROR=y
to be used along with `make W=1` for x86_32 by both compilers.
> But if it's an issue, we could do something like this in
> <asm-generic/pgtable-nopmd.h>:
>
> #if defined(PTRS_PER_PMD) && (PTRS_PER_PMD != 1)
> # error "mm: Wait a minute, that's a super confusing pagetable setup ..."
> #endif
>
> ?
>
> Thanks,
>
> Ingo
>
> =========================>
> From: Ingo Molnar <mingo@xxxxxxxxxx>
> Date: Thu, 6 Mar 2025 22:53:49 +0100
> Subject: [PATCH] x86/mm: Define PTRS_PER_PMD for assembly code too
>
> Andy reported the following build warning from head_32.S:
>
> In file included from arch/x86/kernel/head_32.S:29:
> arch/x86/include/asm/pgtable_32.h:59:5: error: "PTRS_PER_PMD" is not defined, evaluates to 0 [-Werror=undef]
> 59 | #if PTRS_PER_PMD > 1
>
> The reason is that on 2-level i386 paging the folded in PMD's
> PTRS_PER_PMD constant is not defined in assembly headers,
> only in generic MM C headers.
>
> Instead of trying to fish out the definition from the generic
> headers, just define it - it even has a comment for it already...
>
> Reported-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> ---
> arch/x86/include/asm/pgtable-2level_types.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/pgtable-2level_types.h b/arch/x86/include/asm/pgtable-2level_types.h
> index 7f6ccff0ba72..4a12c276b181 100644
> --- a/arch/x86/include/asm/pgtable-2level_types.h
> +++ b/arch/x86/include/asm/pgtable-2level_types.h
> @@ -23,17 +23,17 @@ typedef union {
> #define ARCH_PAGE_TABLE_SYNC_MASK PGTBL_PMD_MODIFIED
>
> /*
> - * traditional i386 two-level paging structure:
> + * Traditional i386 two-level paging structure:
> */
>
> #define PGDIR_SHIFT 22
> #define PTRS_PER_PGD 1024
>
> -
> /*
> - * the i386 is two-level, so we don't really have any
> - * PMD directory physically.
> + * The i386 is two-level, so we don't really have any
> + * PMD directory physically:
> */
> +#define PTRS_PER_PMD 1
Should I give a try?
Okay, just
Tested-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
for x86_32 with Clang 19.1.7 and GCC 14.2.0.
--
With Best Regards,
Andy Shevchenko
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