Re: [PATCH v3 4/5] x86: Port the basic alternative mechanism from Linux to Xen

["Jan Beulich" <JBeulich@suse.com>]

>>> On 03.06.14 at 15:05, <feng.wu@intel.com> wrote:

> 
>> -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@suse.com]
>> Sent: Tuesday, June 03, 2014 6:00 PM
>> To: Wu, Feng
>> Cc: andrew.cooper3@citrix.com; ian.campbell@citrix.com;
>> stefano.stabellini@citrix.com; keir.xen@gmail.com; xen-devel@lists.xen.org;
>> boris.ostrovsky@oracle.com; tim@xen.org 
>> Subject: Re: [PATCH v3 4/5] x86: Port the basic alternative mechanism from
>> Linux to Xen
>> 
>> >>> On 30.05.14 at 10:56, <feng.wu@intel.com> wrote:
>> > +#ifdef K8_NOP1
>> > +static const unsigned char k8nops[] __initconst = {
>> > +    K8_NOP1,
>> > +    K8_NOP2,
>> > +    K8_NOP3,
>> > +    K8_NOP4,
>> > +    K8_NOP5,
>> > +    K8_NOP6,
>> > +    K8_NOP7,
>> > +    K8_NOP8
>> > +};
>> > +static const unsigned char * const k8_nops[ASM_NOP_MAX+1] __initconst =
>> {
>> > +    NULL,
>> > +    k8nops,
>> > +    k8nops + 1,
>> > +    k8nops + 1 + 2,
>> > +    k8nops + 1 + 2 + 3,
>> > +    k8nops + 1 + 2 + 3 + 4,
>> > +    k8nops + 1 + 2 + 3 + 4 + 5,
>> > +    k8nops + 1 + 2 + 3 + 4 + 5 + 6,
>> > +    k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7
>> > +};
>> > +#endif
>> > +
>> > +#ifdef P6_NOP1
>> > +static const unsigned char p6nops[] __initconst = {
>> > +    P6_NOP1,
>> > +    P6_NOP2,
>> > +    P6_NOP3,
>> > +    P6_NOP4,
>> > +    P6_NOP5,
>> > +    P6_NOP6,
>> > +    P6_NOP7,
>> > +    P6_NOP8
>> > +};
>> > +static const unsigned char * const p6_nops[ASM_NOP_MAX+1] __initconst =
>> {
>> > +    NULL,
>> > +    p6nops,
>> > +    p6nops + 1,
>> > +    p6nops + 1 + 2,
>> > +    p6nops + 1 + 2 + 3,
>> > +    p6nops + 1 + 2 + 3 + 4,
>> > +    p6nops + 1 + 2 + 3 + 4 + 5,
>> > +    p6nops + 1 + 2 + 3 + 4 + 5 + 6,
>> > +    p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7
>> > +};
>> > +#endif
>> 
>> The uses of __initconst together with -fPIC cause build problems on
>> older gcc. I fixed this up in a temporary way, but put a work item on
>> my todo list to deal with this properly while at once converting
>> alternative.o to alternative.init.o (as the file consists of only init
>> code and data).
> 
> BTW, is there any difference after converting alternative.o to 
> alternative.init.o, since
> everything in alternative.c has already been __init__?

Yes, there is: String literals will also get moved to .init.*. Plus
inadvertent addition of non-init code/date would get detected at
build time.

Jan