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

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Date:	Fri, 20 Feb 2015 20:21:45 +0100
From:	Alexander Graf <agraf@...e.de>
To:	Michael Mueller <mimu@...ux.vnet.ibm.com>
Cc:	Richard Henderson <rth@...ddle.net>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Gleb Natapov <gleb@...nel.org>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	"Jason J. Herne" <jjherne@...ux.vnet.ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Andreas Faerber <afaerber@...e.de>
Subject: Re: [Qemu-devel] [RFC PATCH v2 10/15] cpu-model/s390: Add cpu class initialization routines




> Am 20.02.2015 um 19:59 schrieb Michael Mueller <mimu@...ux.vnet.ibm.com>:
> 
> On Fri, 20 Feb 2015 10:11:55 -0800
> Richard Henderson <rth@...ddle.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>
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