Re: sparse error on __int128

[Tony Camuso <tcamuso@redhat.com>]

On 01/04/2016 07:08 PM, Luc Van Oostenryck wrote:
> On Tue, Aug 11, 2015 at 07:32:31AM -0400, Tony Camuso wrote:
>> I think I've raised this question before, but I don't think I
>> got a response that indicated whether this is a sparse bug or
>> if there was a source or compile issue.
>>
>> Here is the error:
>> sparse /work/rh7/drivers/net/wireless/rtlwifi/rtl8723com/fw_common.i
>> /work/rh7/drivers/net/wireless/rtlwifi/rtl8723com/fw_common.i:5505:26: error: impossible combination of type specifiers: unsigned __int128
>> /work/rh7/drivers/net/wireless/rtlwifi/rtl8723com/fw_common.i:5505:26: error: Expected ) at end of cast operator
>> /work/rh7/drivers/net/wireless/rtlwifi/rtl8723com/fw_common.i:5505:26: error: got __int128
>>
>> Here is the offending line in context:
>>
>>   5503 static inline __attribute__((no_instrument_function)) u64 mul_u64_u32_shr(u64 a, u32 mul, unsigned int shift)
>>   5504 {
>>   5505  return (u64)(((unsigned __int128)a * mul) >> shift);
>>   5506 }
>>
>
>
> Hi,
>
> There is no source or compile issue here.
> It's just that __int128 is only defined by gcc on x86_64
> but is not defined by sparse.
>
> Now, __int128 is only used twice in the kernel:
> (mul_u64_u32_shr() & mul_u64_u64_shr()) and then only if
> supported by the platform and if __SIZEOF_INT128__ is defined.
> Since sparse doesn't define __SIZEOF_INT128__ there shouldn't be any problems
> but you have used sparse not on the code itself but on preprocessed code by gcc.
> If you run sparse directly on the C code or more simply by using "make C=1 ..."
> to build kernel code, no such problem occurs.
>
> Now, of course, one could argue that sparse should also define __int128
> on platforms where gcc define it, on x86_64 thus.

Hi, Luc.

Thank you for responding. We are using preprocessor files, because what we're
trying to do is to use sparse to identify exported symbols and all their
dependencies, so we need to pull in the .h files, which the preprocessor does
for us.

So, I will apply the argument you so graciously supplied and posit that sparse
should define __int128 on platforms where gcc defines it, e.g. x86_64. :)

It doesn't seem like a very intrusive change.

>
> Regards,
> Luc
>