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Subject: Re: GCC bug ? Re: [PATCH v2 10/10] powerpc/32s: Implement Kernel
 Userspace Access Protection
To:     Segher Boessenkool <segher@kernel.crashing.org>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, ruscur@russell.cc,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <cover.1552292207.git.christophe.leroy@c-s.fr>
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 <a008a182-f1db-073c-7d38-27bfd1fd8676@c-s.fr>
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From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <8501a33e-6c76-b6bd-9d8e-985313f94579@c-s.fr>
Date:   Wed, 22 Jan 2020 07:57:15 +0100
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Le 21/01/2020 à 20:55, Segher Boessenkool a écrit :
> On Tue, Jan 21, 2020 at 05:22:32PM +0000, Christophe Leroy wrote:
>> g1() should return 3, not 5.
> 
> What makes you say that?
> 
> "A return of 0 does not indicate that the
>   value is _not_ a constant, but merely that GCC cannot prove it is a
>   constant with the specified value of the '-O' option."
> 

GCC doc also says:

"if you use it in an inlined function and pass an argument of the 
function as the argument to the built-in, GCC never returns 1 when you 
call the inline function with a string constant"

Does GCC considers (void*)0 as a string constant ?

Christophe