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SubjectRe: [PATCH 05/21] powerpc: Avoid comparison of unsigned long >= 0 in pfn_valid
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Le 04/03/2018 à 11:55, Michael Ellerman a écrit :
> Mathieu Malaterre <malat@debian.org> writes:
>
>> Rewrite comparison since all values compared are of type `unsigned long`.
>>
>> Fix a warning (treated as error in W=1):
>>
>> CC arch/powerpc/kernel/irq.o
>> In file included from ./include/linux/bug.h:5:0,
>> from ./include/linux/cpumask.h:13,
>> from ./include/linux/smp.h:13,
>> from ./include/linux/kernel_stat.h:5,
>> from arch/powerpc/kernel/irq.c:35:
>> ./include/linux/dma-mapping.h: In function ‘dma_map_resource’:
>> ./arch/powerpc/include/asm/page.h:129:32: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
>> #define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr)
>> ^
>> Suggested-by: Segher Boessenkool <segher@kernel.crashing.org>
>> Signed-off-by: Mathieu Malaterre <malat@debian.org>
>> ---
>> arch/powerpc/include/asm/page.h | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
>> index 8da5d4c1cab2..19dea64e7ed2 100644
>> --- a/arch/powerpc/include/asm/page.h
>> +++ b/arch/powerpc/include/asm/page.h
>> @@ -126,7 +126,8 @@ extern long long virt_phys_offset;
>>
>> #ifdef CONFIG_FLATMEM
>> #define ARCH_PFN_OFFSET ((unsigned long)(MEMORY_START >> PAGE_SHIFT))
>> -#define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr)
>> +#define pfn_valid(pfn) \
>> + (((pfn) - ARCH_PFN_OFFSET) < (max_mapnr - ARCH_PFN_OFFSET))
>
> I'm not a big fan of this one, because the original code is *far* more
> obvious as to what it's doing.
>
> I'm not sure if we can make this one a static inline, or whether that
> would help, but it would be worth investigating.
>

The following seems to give a good result:

diff --git a/arch/powerpc/include/asm/page.h
b/arch/powerpc/include/asm/page.h
index 8da5d4c1cab2..6f74938483b7 100644
--- a/arch/powerpc/include/asm/page.h
+++ b/arch/powerpc/include/asm/page.h
@@ -126,7 +126,15 @@ extern long long virt_phys_offset;

#ifdef CONFIG_FLATMEM
#define ARCH_PFN_OFFSET ((unsigned long)(MEMORY_START >> PAGE_SHIFT))
-#define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr)
+#ifndef __ASSEMBLY__
+extern unsigned long max_mapnr;
+static inline bool pfn_valid(unsigned long pfn)
+{
+ unsigned long min_pfn = ARCH_PFN_OFFSET;
+
+ return pfn >= min_pfn && pfn < max_mapnr;
+}
+#endif
#endif

#define virt_to_pfn(kaddr) (__pa(kaddr) >> PAGE_SHIFT)

Christophe

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