Am 29.01.2016 um 00:56 schrieb Nicolai Stange:
> Commit 16da306849d0 ("um: kill pfn_t")
> introduced a compile warning for defconfig:
>
> arch/um/kernel/skas/mmu.c:38:206: warning: right shift count >= width of
> type
> [-Wshift-count-overflow]
>
> Aforementioned patch changes the definition of the phys_to_pfn() macro from
>
> ((pfn_t) ((p) >> PAGE_SHIFT))
>
> to
>
> ((p) >> PAGE_SHIFT)
>
> This effectively changes the phys_to_pfn() expansion's type from
> unsigned long long to unsigned long.
>
> Through the callchain init_stub_pte()->mk_pte(), the expansion of
> phys_to_pfn() is (indirectly) fed into the 'phys' argument of the
> pte_set_val(pte, phys, prot) macro, eventually leading to
>
> (pte).pte_high = (phys) >> 32;
>
> This results in the warning from above.
>
> Since UML only deals with 32 bit addresses, the upper 32 bits from 'phys'
> used to be zero anyway.
>
> Zero out the pte value's high part in pte_set_val() in order to get rid
> of the offending shift.
>
> Fixes: 16da306849d0 ("um: kill pfn_t")
> Signed-off-by: Nicolai Stange <nicsta...@gmail.com>
> ---
> arch/um/include/asm/page.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/um/include/asm/page.h b/arch/um/include/asm/page.h
> index e13d41c..61e235f 100644
> --- a/arch/um/include/asm/page.h
> +++ b/arch/um/include/asm/page.h
> @@ -46,8 +46,8 @@ typedef struct { unsigned long pgd; } pgd_t;
> smp_wmb(); \
> (to).pte_low = (from).pte_low; })
> #define pte_is_zero(pte) (!((pte).pte_low & ~_PAGE_NEWPAGE) &&
> !(pte).pte_high)
> -#define pte_set_val(pte, phys, prot) \
> - ({ (pte).pte_high = (phys) >> 32; \
> +#define pte_set_val(pte, phys, prot) \
> + ({ (pte).pte_high = 0; \
> (pte).pte_low = (phys) | pgprot_val(prot); })
I think we can completely kill .pte_high.
Thanks,
//richard
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