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

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Tuesday, June 03, 2014 9:10 PM
> To: Wu, Feng
> Cc: andrew.cooper3@xxxxxxxxxx; ian.campbell@xxxxxxxxxx;
> stefano.stabellini@xxxxxxxxxx; keir.xen@xxxxxxxxx; xen-devel@xxxxxxxxxxxxx;
> boris.ostrovsky@xxxxxxxxxx; tim@xxxxxxx
> Subject: RE: [PATCH v3 4/5] x86: Port the basic alternative mechanism from
> Linux to Xen
> 
> >>> On 03.06.14 at 15:05, <feng.wu@xxxxxxxxx> wrote:
> 
> >
> >> -----Original Message-----
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: Tuesday, June 03, 2014 6:00 PM
> >> To: Wu, Feng
> >> Cc: andrew.cooper3@xxxxxxxxxx; ian.campbell@xxxxxxxxxx;
> >> stefano.stabellini@xxxxxxxxxx; keir.xen@xxxxxxxxx;
> xen-devel@xxxxxxxxxxxxx;
> >> boris.ostrovsky@xxxxxxxxxx; tim@xxxxxxx
> >> 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@xxxxxxxxx> 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

Thanks, good to know this!

Feng


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