Re: [PATCH v2] librte_eal/common: Fix cast from pointer to integer of different size

[Pawel Wodkowski <pawelx.wodkowski-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On 2015-03-04 02:58, Qiu, Michael wrote:
> On 3/3/2015 9:38 PM, Wodkowski, PawelX wrote:
>>> -----Original Message-----
>>> From: Qiu, Michael
>>> Sent: Tuesday, March 03, 2015 11:00 AM
>>> To: Wodkowski, PawelX; dev-VfR2kkLFssw@public.gmane.org
>>> Subject: Re: [dpdk-dev] [PATCH v2] librte_eal/common: Fix cast from pointer to
>>> integer of different size
>>>
>>> On 3/3/2015 4:25 PM, Wodkowski, PawelX wrote:
>>>> On 2015-03-03 03:20, Michael Qiu wrote:
>>>>> /i686-native-linuxapp-gcc/include/rte_memcpy.h:592:23: error:
>>>>> cast from pointer to integer of different size
>>>>> [-Werror=pointer-to-int-cast]
>>>>>
>>>>>     dstofss = 16 - (int)((long long)(void *)dst & 0x0F) + 16;
>>>>>
>>>>> Type 'long long' is 64-bit in i686 platform while 'void *'
>>>>> is 32-bit.
>>>>>
>>>>> Signed-off-by: Michael Qiu <michael.qiu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
>>>>> ---
>>>>> v2 --> v1:
>>>>> 	Remove unnecessary casting (void *)
>>>>>
>>>>>    lib/librte_eal/common/include/arch/x86/rte_memcpy.h | 4 ++--
>>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
>>> b/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
>>>>> index 7b2d382..85a5f4d 100644
>>>>> --- a/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
>>>>> +++ b/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
>>>>> @@ -589,12 +589,12 @@ COPY_BLOCK_64_BACK15:
>>>>>    	 * unaligned copy functions require up to 15 bytes
>>>>>    	 * backwards access.
>>>>>    	 */
>>>>> -	dstofss = 16 - (int)((long long)(void *)dst & 0x0F) + 16;
>>>>> +	dstofss = 16 - (int)((long)dst & 0x0F) + 16;
>>>>>    	n -= dstofss;
>>>>>    	rte_mov32((uint8_t *)dst, (const uint8_t *)src);
>>>>>    	src = (const uint8_t *)src + dstofss;
>>>>>    	dst = (uint8_t *)dst + dstofss;
>>>>> -	srcofs = (int)((long long)(const void *)src & 0x0F);
>>>>> +	srcofs = (int)((long)src & 0x0F);
>>>>>
>>>>>    	/**
>>>>>    	 * For aligned copy
>>>>>
>>>> I think you should use here size_t, (u)ptrdiff_t or (u)intptr_t as this
>>> Yes, but 'long' is enough, does it limit anything, or has any issue with
>>> multiple platforms?
>>>
>> Those types ((u)ptrdiff_t, (u)intptr_t) exists specially for
>> pointer-to-int and int-to-pointer casts. Using integer primitives might
>> produce further warnings/error in the future and need further patches
>> fixing the same place.
>
> OK, I will send out the v3 patch.
>
>> Also why make offset variables signed and different type? This introduce
>> a lot of unnecessary explicit and implicit casts or type promotions.
>
> But Is it suitable to make offset (u)ptrdiff_t or (u)intptr_t?
>

I think, as final result is offset, its type should be size_t (the same 
type as type of offsetof() macro). This way you can use 
uptrdiff_t/uintptr_t and does not need of any signed-unsigned casting.

> Thanks,
> Michael
>
>>>> will be more portable.
>>>> Also type of dstofss and srcofs should be changed accordingly.
>>> No, I think, it should be offset.
>>>
>>> Thanks,
>>> Michael
>>
>
>


-- 
Pawel