Re: [PATCH v4 15/17] x86/traps: Fixup general protection faults caused by UMIP

[H. Peter Anvin]

Luck <tony.luck@xxxxxxxxx>
From: hpa@xxxxxxxxx
Message-ID: <C4474E45-EAE0-45D3-8DB1-78AA1C2548A8@xxxxxxxxx>

On February 24, 2017 11:36:19 AM PST, Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx> wrote:
>On Fri, 2017-02-24 at 11:11 -0800, Andy Lutomirski wrote:
>> > In a previous version Andy Lutomirsky suggested that
>> >         if (user_mode(regs) && (fixup_umip_exception(regs) == 0))
>> >
>> > was easier to read :). Although at the time fixup_umip_exception
>> > returned a numeric value. Now it only returns true/false for
>> > successful/failed emulation. If with true/false not comparing to
>> true
>> > makes it easier to read, I will make the change.
>> 
>> I think == true is silly :)
>
>Then I'll make the change.
>
>Thanks and BR,
>Ricardo

It's worse than silly, it is potentially toxic.

true is a macro which it's defined as 1.  Thus

     foo == true

... doesn't actually mean what people *think* it does, which is roughly the same thing as

    !!foo

However, if foo is not a boolean, this is *very* different; consider if foo is 2.
-- 
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