Re [PATCH] x86/CET: Fix build following c/s 43b98e7190

[Jan Beulich <jbeulich@xxxxxxxx>]

> OSSTest reports:
> 
>   x86_64.S: Assembler messages:
>   x86_64.S:57: Error: no such instruction: `setssbsy'
>   /home/osstest/build.150510.build-amd64/xen/xen/Rules.mk:183: recipe for 
> target 'head.o' failed
>   make[4]: Leaving directory 
> '/home/osstest/build.150510.build-amd64/xen/xen/arch/x86/boot'
>   make[4]: *** [head.o] Error 1
> 
> All use of CET instructions, even those inside alternative blocks, needs to be
> behind CONFIG_XEN_SHSTK, as it indicates suitable toolchain support.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

That's quite a bit of #ifdef-ary here. Simple (operand-less) insns
like SETSSBSY could easily be made available via .byte directives.
Would you be amenable to to ack-ing a patch to replace some of the
#ifdef-s (at least the ones at the lstar, cstar, and sysenter
entry points), after 4.14?

Jan