Re: [PATCH] x86/shadow: don't use #if in macro invocations

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 18/02/2026 9:03 am, Jan Beulich wrote:
> As per the standard this is UB, i.e. we're building on a defacto extension
> in the compilers we use. Misra C:2012 rule 20.6 disallows this altogether,
> though. Use helper always-inline functions instead.
>
> In sh_audit_l1_table(), along with reducing the scope of "gfn", which now
> isn't used anymore by the if() side of the conditional, also reduce the
> scope of two other adjacent variables.
>
> For audit_magic() note that both which parameters are needed and what
> their types are is attributed to AUDIT_FAIL() accessing variables which
> aren't passed as arguments to it.
>
> No functional change intended. Of course codegen does change with this,
> first and foremost in register allocation.
>
> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

I included this patch on an interim branch of other MISRA fixes of mine
to get a run.

https://gitlab.com/xen-project/hardware/xen-staging/-/jobs/13198988953

There's one more violation still to fix:

    if ( unlikely((level == 1)
                  && sh_mfn_is_a_page_table(target_mfn)
#if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC )
                  /* Unless the page is out of sync and the guest is
                     writing to it. */
                  && !(mfn_oos_may_write(target_mfn)
                       && (ft == ft_demand_write))
#endif /* OOS */
                  ) )
        sflags &= ~_PAGE_RW;



I also looked at this one previously.  Making mfn_oos_may_write()
visible outside of SHOPT_OUT_OF_SYNC is quite invasive.

Here, I suggest dropping the unlikely() as the easiest fix.  It's almost
certainly useless anyway.

~Andrew