From: Segher Boessenkool <segher@kernel.crashing.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
Paul Mackerras <paulus@samba.org>,
Anatolij Gustschin <agust@denx.de>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] powerpc: mpc5200: Remove VLA usage
Date: Mon, 2 Jul 2018 12:16:31 -0500 [thread overview]
Message-ID: <20180702171631.GA16221@gate.crashing.org> (raw)
In-Reply-To: <87fu12mnf7.fsf@concordia.ellerman.id.au>
On Mon, Jul 02, 2018 at 11:33:32AM +1000, Michael Ellerman wrote:
> What if we write it:
>
> char saved_0x500[0x600 - 0x500];
>
> Hopefully the compiler is smart enough not to generate a VLA for that :)
It is a VLA if the array size is not an integer constant expression. This
is defined by C; the compiler has nothing to do with it. 0x600-0x500 is
an integer constant expression, so this is not a VLA.
But if you meant if GCC will ever do a dynamic stack allocation for a fixed
size local variable: yes indeed, I hope not!
(Sometimes GCC can avoid this even with VLAs; but in this example we do
not even have a VLA, so it's easier than that :-) )
Segher
next prev parent reply other threads:[~2018-07-02 17:16 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-29 18:53 [PATCH] powerpc: mpc5200: Remove VLA usage Kees Cook
2018-06-29 21:02 ` Arnd Bergmann
2018-06-29 21:44 ` Kees Cook
2018-07-02 1:33 ` Michael Ellerman
2018-07-02 15:52 ` Kees Cook
2018-07-02 17:16 ` Segher Boessenkool [this message]
2018-07-03 1:41 ` Michael Ellerman
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