linux-kernel - RE: [PATCH] drivers: net: wireless: ath: ath9: dfs: remove VLA usage

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Date:   Tue, 13 Mar 2018 12:32:17 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Daniel Micay' <danielmicay@...il.com>,
        Arend van Spriel <arend.vanspriel@...adcom.com>
CC:     Andreas Christoforou <andreaschristofo@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        QCA ath9k Development <ath9k-devel@....qualcomm.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] drivers: net: wireless: ath: ath9: dfs: remove VLA usage

From: Daniel Micay
> Sent: 10 March 2018 23:45
> 
> > Just wondering. Is this actually a VLA. FFT_NUM_SAMPLES was static const so
> > not really going to show a lot of variation. This array will always have the
> > same size on the stack.
> 
> The issue is that unlike in C++, a `static const` can't be used in a
> constant expression in C. It's unclear why C is defined that way but
> it's how it is and there isn't currently a GCC extension making more
> things into constant expressions like C++.

'static' and 'const' are both just qualifiers to a 'variable'
You can still take it's address.
The language allows you to cast away the 'const' and write to
the variable - the effect is probably 'implementation defined'.

It is probably required to be valid for 'static const' items
to be patchable.

	David