From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.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>,
"Tobin C. Harding" <me@tobin.cc>,
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 <rdunlap@infra
Subject: Re: [PATCH v3] kernel.h: Skip single-eval logic on literals in min()/max()
Date: Mon, 12 Mar 2018 16:57:59 -0700 [thread overview]
Message-ID: <CA+55aFwK7W0SsaP5eR+2TxOj-j_Mu_E11fRw2Gk8ptV71ebvww@mail.gmail.com> (raw)
In-Reply-To: <20180312155524.b421f07d7f08f24c57bd1887@linux-foundation.org>
On Mon, Mar 12, 2018 at 3:55 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> Replacing the __builtin_choose_expr() with ?: works of course.
Hmm. That sounds like the right thing to do. We were so myopically
staring at the __builtin_choose_expr() problem that we overlooked the
obvious solution.
Using __builtin_constant_p() together with a ?: is in fact our common
pattern, so that should be fine. The only real reason to use
__builtin_choose_expr() is if you want to get the *type* to vary
depending on which side you choose, but that's not an issue for
min/max.
> What will be the runtime effects?
There should be none. Gcc will turn the conditional for the ?: into a
constant, and DTRT.
Linus
next prev parent reply other threads:[~2018-03-12 23:57 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-09 20:05 [PATCH v3] kernel.h: Skip single-eval logic on literals in min()/max() Kees Cook
2018-03-09 21:10 ` Linus Torvalds
2018-03-09 21:47 ` Kees Cook
2018-03-11 22:46 ` Tobin C. Harding
2018-03-13 13:31 ` David Laight
2018-03-10 0:07 ` Andrew Morton
2018-03-10 0:28 ` Linus Torvalds
2018-03-10 0:32 ` Andrew Morton
2018-03-10 0:38 ` Linus Torvalds
2018-03-10 1:30 ` Kees Cook
2018-03-10 1:31 ` Kees Cook
2018-03-10 2:37 ` Linus Torvalds
[not found] ` <20180310023907.798690563@goodmis.org>
2018-03-10 3:10 ` [PATCH 3/3] tracing: Rewrite filter logic to be simpler and faster Steven Rostedt
2018-03-10 3:15 ` Steven Rostedt
2018-03-10 3:22 ` Steven Rostedt
2018-03-12 22:55 ` [PATCH v3] kernel.h: Skip single-eval logic on literals in min()/max() Andrew Morton
2018-03-12 23:57 ` Linus Torvalds [this message]
2018-03-13 4:28 ` Kees Cook
2018-03-13 21:02 ` Andrew Morton
2018-03-13 22:14 ` Kees Cook
2018-03-14 11:35 ` David Laight
2018-03-10 3:11 ` Randy Dunlap
2018-03-10 6:10 ` Miguel Ojeda
2018-03-10 7:03 ` Miguel Ojeda
2018-03-10 16:04 ` Linus Torvalds
2018-03-10 15:33 ` Kees Cook
2018-03-10 16:11 ` Linus Torvalds
2018-03-10 16:30 ` Linus Torvalds
2018-03-10 17:34 ` Miguel Ojeda
2018-03-10 17:51 ` Linus Torvalds
2018-03-10 19:08 ` Miguel Ojeda
2018-03-11 11:05 ` Ingo Molnar
2018-03-11 18:23 ` Linus Torvalds
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