Re: [PATCH -tip v3 1/2] x86: xen: insn: Decode Xen and KVM emulate-prefix signature

Masami Hiramatsu
2019-09-06T10:28:29Z

On Fri, 6 Sep 2019 09:34:36 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, Sep 06, 2019 at 10:45:48AM +0900, Masami Hiramatsu wrote:
>
> > diff --git a/arch/x86/include/asm/xen/interface.h b/arch/x86/include/asm/xen/interface.h
> > index 62ca03ef5c65..fe33a9798708 100644
> > --- a/arch/x86/include/asm/xen/interface.h
> > +++ b/arch/x86/include/asm/xen/interface.h
> > @@ -379,12 +379,15 @@ struct xen_pmu_arch {
> > * Prefix forces emulation of some non-trapping instructions.
> > * Currently only CPUID.
> > */
> > +#include <asm/xen/prefix.h>
> > +
> > #ifdef __ASSEMBLY__
> > -#define XEN_EMULATE_PREFIX .byte 0x0f,0x0b,0x78,0x65,0x6e ;
> > +#define XEN_EMULATE_PREFIX .byte __XEN_EMULATE_PREFIX ;
> > #define XEN_CPUID XEN_EMULATE_PREFIX cpuid
> > #else
> > -#define XEN_EMULATE_PREFIX ".byte 0x0f,0x0b,0x78,0x65,0x6e ; "
> > +#define XEN_EMULATE_PREFIX ".byte " __XEN_EMULATE_PREFIX_STR " ; "
> > #define XEN_CPUID XEN_EMULATE_PREFIX "cpuid"
> > +
> > #endif
>
> Possibly you can do something like:
>
> #define XEN_EMULATE_PREFIX __ASM_FORM(.byte __XEN_EMULATE_PREFIX ;)
> #define XEN_CPUID XEN_EMULATE_PREFIX __ASM_FORM(cpuid)

Oops, this doesn't work, since __ASM_FORM(x) uses #x directly

# define __ASM_FORM(x) " " #x " "

which doesn't expand "x" if x is a macro. We have to use __stringify
like

# include <linux/stringify.h>
# define __ASM_FORM(x) " " __stringify(x) " "

So this needs aonther patch in the series :)

Thank you,

--
Masami Hiramatsu <mhiramat@kernel.org>