From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2 02/10] netfilter: Avoid assigning 'const' pointer to
 non-const pointer
Date: Fri, 24 Jan 2020 09:24:43 +0100
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To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Will Deacon <will@kernel.org>, LKML <linux-kernel@vger.kernel.org>, linux-arch <linux-arch@vger.kernel.org>, kernel-team <kernel-team@android.com>, Michael Ellerman <mpe@ellerman.id.au>, Linus Torvalds <torvalds@linux-foundation.org>, Segher Boessenkool <segher@kernel.crashing.org>, Christian Borntraeger <borntraeger@de.ibm.com>, Luc Van Oostenryck <luc.vanoostenryck@gmail.com>, Arnd Bergmann <arnd@arndb.de>, Peter Oberparleiter <oberpar@linux.ibm.com>, Masahiro Yamada <masahiroy@kernel.org>, Pablo Neira Ayuso <pablo@netfilter.org>, Jozsef Kadlecsik <kadlec@netfilter.org>, Florian Westphal <fw@strlen.de>, "David S. Miller" <davem@davemloft.net>

On Thu, Jan 23, 2020 at 11:07:59AM -0800, Nick Desaulniers wrote:

> Good thing it's the variable being modified was not declared const; I
> get spooked when I see -Wdiscarded-qualifiers because of Section
> 6.7.3.6 of the ISO C11 draft spec:
> 
> ```
> If an attempt is made to modify an object defined with a
> const-qualified type through use
> of an lvalue with non-const-qualified type, the behavior is undefined.
> If an attempt is
> made to refer to an object defined with a volatile-qualified type
> through use of an lvalue
> with non-volatile-qualified type, the behavior is undefined.133)
> 
> 133) This applies to those objects that behave as if they were defined
> with qualified types, even if they are
> never actually defined as objects in the program (such as an object at
> a memory-mapped input/output
> address).
> ```
> 
> Which is about the modification of a const-declared variable (explicit
> UB which Clang actively exploits), 

Just for curiosity's sake. What does clang actually do in that case?