Re: [PATCH 54/65] x86/stack: Annotate fnptr targets

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.11.2021 13:34, Andrew Cooper wrote:
> --- a/xen/include/asm-x86/current.h
> +++ b/xen/include/asm-x86/current.h
> @@ -173,7 +173,6 @@ unsigned long get_stack_dump_bottom (unsigned long sp);
>  #define switch_stack_and_jump(fn, instr, constr)                        \
>      ({                                                                  \
>          unsigned int tmp;                                               \
> -        (void)((fn) == (void (*)(void))NULL);                           \
>          BUILD_BUG_ON(!ssaj_has_attr_noreturn(fn));                      \
>          __asm__ __volatile__ (                                          \
>              SHADOW_STACK_WORK                                           \
> @@ -198,6 +197,7 @@ unsigned long get_stack_dump_bottom (unsigned long sp);
>  
>  /* The constraint may only specify non-call-clobbered registers. */
>  #define reset_stack_and_jump_ind(fn)                                    \
> +    (void)((fn) == (void (*)(void))NULL);                               \
>      switch_stack_and_jump(fn, "INDIRECT_JMP %", "b")
>  

While the risk of use in a context really requiring it is low, I
still think we'd be better off wrapping the whole thing in ({ })
then.

Jan