Re: [PATCHv3 1/5] efi/runtime-wrappers: detect FW irq flag corruption

[Robin Murphy]

On 25/04/16 15:24, Matt Fleming wrote:
> On Mon, 25 Apr, at 04:18:41PM, Ard Biesheuvel wrote:
> > On 25 April 2016 at 16:15, Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> wrote:
> > > On Mon, 25 Apr, at 03:12:01PM, Robin Murphy wrote:
> > > > > +static void efi_call_virt_check_flags(unsigned long flags, const char *call)
> > > > > +{
> > > > > +    unsigned long cur_flags;
> > > > > +    bool mismatch;
> > > > > +
> > > > > +    local_save_flags(cur_flags);
> > > > > +
> > > > > +    mismatch = !!((cur_flags ^ flags) & ARCH_EFI_IRQ_FLAGS_MASK);
> > > >
> > > > nit: the assignment itself is already a conversion to bool, so the
> > > > excitement is redundant here.
> > >
> > > This was intentional. I asked Mark to make this change so that it's
> > > explicit for the developer that we're performing the type conversion.
> >
> > But replacing an implicit boolean cast with an explicit one makes
> > little sense, no? Don't we simply want '!= 0' here if you need a
> > boolean expression?
>
> Aha but '!!' is fewer characters to type!!
>
> I'm not that bothered as long as we don't stuff an int into a bool
> without giving the programmer some idea we're doing that. It's not
> about the compiler getting it wrong, more about a developer
> introducing a bug when they change the code in the future.
>
> Unless anyone objects, I'll fix this up to use '!= 0' when I apply it.

Agreed - the belt and braces approach isn't necessarily bad if the cost
of cocking it up is significant, and !=0 is as explicit as you can get.
After all, if Joe Random Hacker can't infer the behaviour from looking 4
lines up to see the variable definition, then I wouldn't count on him
understanding !! either ;)

Thanks,
Robin.

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