Re: [PATCH v2 2/6] x86: reduce CET-SS related #ifdef-ary

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/09/2020 13:30, Jan Beulich wrote:
> Commit b586a81b7a90 ("x86/CET: Fix build following c/s 43b98e7190") had
> to introduce a number of #ifdef-s to make the build work with older tool
> chains. Introduce an assembler macro covering for tool chains not
> knowing of CET-SS, allowing some conditionals where just SETSSBSY is the
> problem to be dropped again.
>
> No change to generated code.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Now that I've done this I'm no longer sure which direction is better to
> follow: On one hand this introduces dead code (even if just NOPs) into
> CET-SS-disabled builds. Otoh this is a step towards breaking the tool
> chain version dependency of the feature.

I've said before.  You cannot break the toolchain dependency without
hardcoding memory operands.  I'm not prepared to let that happen.

There is no problem requiring newer toolchains for newer features
(you're definitely not having CET-IBT, for example), and there is a
(unacceptably, IMO) large cost to this work.

~Andrew