Re: [Qemu-devel] [RFC PATCH v2 10/15] cpu-model/s390: Add cpu class initialization routines

Alexander Graf
2015-02-20T19:21:46Z

> Am 20.02.2015 um 19:59 schrieb Michael Mueller <mimu@linux.vnet.ibm.com>:
>
> On Fri, 20 Feb 2015 10:11:55 -0800
> Richard Henderson <rth@twiddle.net> wrote:
>
>>> +static inline uint64_t big_endian_bit(unsigned long nr)
>>> +{
>>> + return 1ul << (BITS_PER_LONG - (nr % BITS_PER_LONG));
>>> +};
>>
>> This is buggy. NR=0 should map to 63, not 64.
>
> I'm sure I was asked to replace my constant 64 and 63 with that defines and at the end I messed
> it up... :-(
>
>>
>>> + return !!(*ptr & big_endian_bit(nr));
>>
>> Personally I dislike !! as an idiom. Given that big_endian_bit isn't used
>> anywhere else, can we integrate it and change this to
>>
>> static inline int test_facility(unsigned long nr, uint64_t *fac_list)
>> {
>> unsigned long word = nr / BITS_PER_LONG;
>> unsigned long be_bit = 63 - (nr % BITS_PER_LONG);
>> return (fac_list[word] >> be_bit) & 1;
>> }
>
> Yes, I just use it in this context. I will integrate your version.
>
> BTW I changed the whole facility defining code to be generated by an external helper at compile
> time. That is more simple and safe to change. I will send it with v3. See attachment for an
> example of the generated header file.

Please make sure to use ULL with constants and uint64_t on variables. Long is almost always wrong in QEMU.

Alex

>
> Thanks,
> Michael
>
> <gen-facilities.h>