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 19:59:28 +0100
From:	Michael Mueller <mimu@...ux.vnet.ibm.com>
To:	Richard Henderson <rth@...ddle.net>
Cc:	qemu-devel@...gnu.org, kvm@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
	Gleb Natapov <gleb@...nel.org>, Alexander Graf <agraf@...e.de>,
	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

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.

Thanks,
Michael


View attachment "gen-facilities.h" of type "text/x-chdr" (2453 bytes)