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Message-Id: <20180309163241.a421e216999bd0b1f43a64c2@linux-foundation.org>
Date: Fri, 9 Mar 2018 16:32:41 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kees Cook <keescook@...omium.org>, Linux Kernel Mailing List
<linux-kernel@...r.kernel.org>, Josh Poimboeuf <jpoimboe@...hat.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>, "Gustavo A. R. Silva"
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<rostedt@...dmis.org>, Jonathan Corbet <corbet@....net>, Chris Mason
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"David S. Miller" <davem@...emloft.net>, Alexey Kuznetsov
<kuznet@....inr.ac.ru>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, Ingo
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Subject: Re: [PATCH v3] kernel.h: Skip single-eval logic on literals in
min()/max()
On Fri, 9 Mar 2018 16:28:51 -0800 Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Fri, Mar 9, 2018 at 4:07 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > A brief poke failed to reveal a workaround - gcc-4.4.4 doesn't appear
> > to know that __builtin_constant_p(x) is a constant. Or something.
>
> LOL.
>
> I suspect it might be that it wants to evaluate
> __builtin_choose_expr() at an earlier stage than it evaluates
> __builtin_constant_p(), so it's not that it doesn't know that
> __builtin_constant_p() is a constant, it just might not know it *yet*.
>
> Maybe.
>
> Side note, if it's not that, but just the "complex" expression that
> has the logical 'and' etc, maybe the code could just use
>
> __builtin_constant_p((x)+(y))
>
> or something.
I'll do a bit more poking at it.
> But yeah:
>
> > Sigh. Wasn't there some talk about modernizing our toolchain
> > requirements?
>
> Maybe it's just time to give up on 4.4. We wanted 4.5 for "asm goto",
> and once we upgrade to 4.5 I think Arnd said that no distro actually
> ships it, so we might as well go to 4.6.
>
> So maybe this is just the excuse to finally make that official, if
> there is no clever workaround any more.
I wonder which gcc versions actually accept Kees's addition.
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