Re: [PATCH] x86/cet: Fix build on newer versions of GCC

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Tue, Aug 17, 2021 at 11:56:56AM +0100, Andrew Cooper wrote:
> Some versions of GCC complain with:
> 
>   traps.c:405:22: error: 'get_shstk_bottom' defined but not used 
> [-Werror=unused-function]
>    static unsigned long get_shstk_bottom(unsigned long sp)
>                         ^~~~~~~~~~~~~~~~
>   cc1: all warnings being treated as errors
> 
> Change #ifdef to if ( IS_ENABLED(...) ) to make the sole user of
> get_shstk_bottom() visible to the compiler.
> 
> Fixes: 35727551c070 ("x86/cet: Fix shskt manipulation error with 
> BUGFRAME_{warn,run_fn}")
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> CC: Wei Liu <wl@xxxxxxx>
> CC: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> 
> Not actually tested.  I don't seem to have a new enough GCC to hand.

I have just compile-tested it and it seems to fix the issue (indeed it
failed before with CONFIG_XEN_SHSTK disabled).

> Most of the delta here is indentation.  This diff is more easily reviewed with
> `git show --ignore-all-space`

Wouldn't this make the compiler include the code even if
CONFIG_XEN_SHSTK is disabled (not a huge issue...)? Or is it smart
enough to optimize it out in that case?

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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