From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Tobin C. Harding" <me@tobin.cc>
Subject: Re: [PATCH v3] kernel.h: Skip single-eval logic on literals in
 min()/max()
Date: Mon, 12 Mar 2018 09:46:16 +1100
Message-ID: <20180311224616.GJ16734@eros>
References: <20180309200536.GA5670@beast>
 <CA+55aFy82Drgu2xm1GWaDz2Jyj5QBx3dW4AatXzmCx-b1YET5Q@mail.gmail.com>
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Cc: Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Jonathan Corbet <corbet@lwn.net>, Chris Mason <clm@fb.com>,
        Josef Bacik <jbacik@fb.com>, David Sterba <dsterba@suse.com>,
        "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Borislav Petkov <bp@suse.de>,
        Randy Dunlap <rdun
To: Linus Torvalds <torvalds@linux-foundation.org>
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On Fri, Mar 09, 2018 at 01:10:30PM -0800, Linus Torvalds wrote:
> On Fri, Mar 9, 2018 at 12:05 PM, Kees Cook <keescook@chromium.org> wrote:
> > When max() is used in stack array size calculations from literal values
> > (e.g. "char foo[max(sizeof(struct1), sizeof(struct2))]", the compiler
> > thinks this is a dynamic calculation due to the single-eval logic, which
> > is not needed in the literal case. This change removes several accidental
> > stack VLAs from an x86 allmodconfig build:
> 
> Ok, looks good.
> 
> I just have a couple of questions about applying it.
> 
> In particular, if this will help people working on getting rid of
> VLA's in the short term, I can apply it directly. But if people who
> are looking at it (anybody else than Kees?) don't much care, then this
> might be a 4.17 thing or at least "random -mm queue"?

It's easy enough to work on the other VLA removals without basing on
this, no rush.


thanks,
Tobin.