Re: [PATCH] KVM: x86: fix cocci warnings

From: Nick Desaulniers <ndesaulniers@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	David Bolvansky <david.bolvansky@gmail.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
	Vihas Mak <makvihas@gmail.com>,
	seanjc@google.com, wanpengli@tencent.com, jmattson@google.com,
	joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com,
	bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
	hpa@zytor.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: x86: fix cocci warnings
Date: Tue, 16 Nov 2021 10:16:22 -0800	[thread overview]
Message-ID: <CAKwvOdmy6Fo-FvximsRN+i0sZ5ZgWjWdD-m2fLN-rhvBuqO9mw@mail.gmail.com> (raw)
In-Reply-To: <04b7e240-8e1d-1402-3cef-e65469bd9317@redhat.com>

On Tue, Nov 16, 2021 at 1:50 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 11/15/21 10:59, Vitaly Kuznetsov wrote:
> > One minor remark: 'kvm_set_pte_rmapp()' handler is passed to
> > 'kvm_handle_gfn_range()' which does
> >
> >          bool ret = false;
> >
> >          for_each_slot_rmap_range(...)
> >                  ret |= handler(...);
> >
> > and I find '|=' to not be very natural with booleans. I'm not sure it's
> > worth changing though.
>
> Changing that would be "harder" than it seems because "ret = ret ||
> handler(...)" is wrong, and "|" is even more unnatural than "|=" (so
> much that clang warns about it).
>
> In fact I wonder if "|=" with a bool might end up warning with clang,
> which we should check before applying this patch.  It doesn't seem to be
> in the original commit[1], but better safe than sorry: Nick, does clang
> intend to warn also about "ret |= fn()" and "ret &= fn()"?  Technically,
> it is a bitwise operation with side-effects in the RHS.

I think that warning had more to due with typo's where `||` or `&&`
was meant (to short circuit the side effects) but `|` or `&` was typed
by accident, keeping both side effects.  I'm not sure what the typo
would be in `ret |= fn();`.

>
> Paolo
>
> [1] https://github.com/llvm/llvm-project/commit/f59cc9542bfb461
>

-- 
Thanks,
~Nick Desaulniers