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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@infradead.org>,
	Ian Abbott <abbotti@mev.co.uk>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Petr Mladek <pmladek@suse.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
	Linux Btrfs <linux-btrfs@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH v3] kernel.h: Skip single-eval logic on literals in min()/max()
Date: Fri, 9 Mar 2018 16:28:51 -0800	[thread overview]
Message-ID: <CA+55aFw9hWz1-YFVoHEiXDjqb9q7dz=rQVXr7YLkMuVLvbwaOg@mail.gmail.com> (raw)
In-Reply-To: <20180309160719.154a3158e2d8ee56e43a918f@linux-foundation.org>

On Fri, Mar 9, 2018 at 4:07 PM, Andrew Morton <akpm@linux-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.

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.

                    Linus

WARNING: multiple messages have this Message-ID (diff)
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: Fri, 9 Mar 2018 16:28:51 -0800	[thread overview]
Message-ID: <CA+55aFw9hWz1-YFVoHEiXDjqb9q7dz=rQVXr7YLkMuVLvbwaOg@mail.gmail.com> (raw)
In-Reply-To: <20180309160719.154a3158e2d8ee56e43a918f@linux-foundation.org>

On Fri, Mar 9, 2018 at 4:07 PM, Andrew Morton <akpm@linux-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.

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.

                    Linus

  reply	other threads:[~2018-03-10  0:28 UTC|newest]

Thread overview: 85+ 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 20:05 ` Kees Cook
2018-03-09 21:10 ` Linus Torvalds
2018-03-09 21:10   ` Linus Torvalds
2018-03-09 21:47   ` Kees Cook
2018-03-09 21:47     ` Kees Cook
2018-03-11 22:46   ` Tobin C. Harding
2018-03-11 22:46     ` Tobin C. Harding
2018-03-11 22:46     ` Tobin C. Harding
2018-03-13 13:31   ` David Laight
2018-03-13 13:31     ` David Laight
2018-03-10  0:07 ` Andrew Morton
2018-03-10  0:07   ` Andrew Morton
2018-03-10  0:28   ` Linus Torvalds [this message]
2018-03-10  0:28     ` Linus Torvalds
2018-03-10  0:32     ` Andrew Morton
2018-03-10  0:32       ` Andrew Morton
2018-03-10  0:38       ` Linus Torvalds
2018-03-10  0:38         ` Linus Torvalds
2018-03-10  1:30         ` Kees Cook
2018-03-10  1:30           ` Kees Cook
2018-03-10  1:31           ` Kees Cook
2018-03-10  1:31             ` Kees Cook
2018-03-10  2:37             ` Linus Torvalds
2018-03-10  2:37               ` Linus Torvalds
2018-03-12 22:55           ` Andrew Morton
2018-03-12 22:55             ` Andrew Morton
2018-03-12 23:57             ` Linus Torvalds
2018-03-12 23:57               ` Linus Torvalds
2018-03-13  4:28               ` Kees Cook
2018-03-13  4:28                 ` Kees Cook
2018-03-13 21:02                 ` Andrew Morton
2018-03-13 21:02                   ` Andrew Morton
2018-03-13 22:14                   ` Kees Cook
2018-03-13 22:14                     ` Kees Cook
2018-03-14 11:35                     ` David Laight
2018-03-14 11:35                       ` David Laight
2018-03-10  3:11   ` Randy Dunlap
2018-03-10  3:11     ` Randy Dunlap
2018-03-10  6:10     ` Miguel Ojeda
2018-03-10  6:10       ` Miguel Ojeda
2018-03-10  7:03       ` Miguel Ojeda
2018-03-10  7:03         ` Miguel Ojeda
2018-03-10 16:04         ` Linus Torvalds
2018-03-10 16:04           ` Linus Torvalds
2018-03-10 15:33       ` Kees Cook
2018-03-10 15:33         ` Kees Cook
2018-03-10 16:11         ` Linus Torvalds
2018-03-10 16:11           ` Linus Torvalds
2018-03-10 16:30         ` Linus Torvalds
2018-03-10 16:30           ` Linus Torvalds
2018-03-10 17:34           ` Miguel Ojeda
2018-03-10 17:34             ` Miguel Ojeda
2018-03-10 17:51             ` Linus Torvalds
2018-03-10 17:51               ` Linus Torvalds
2018-03-10 19:08               ` Miguel Ojeda
2018-03-10 19:08                 ` Miguel Ojeda
2018-03-11 11:05               ` Ingo Molnar
2018-03-11 11:05                 ` Ingo Molnar
2018-03-11 18:23                 ` Linus Torvalds
2018-03-11 18:23                   ` Linus Torvalds
2018-03-10  2:34 [PATCH 0/3] tracing: Rewrite the function filter code Steven Rostedt
2018-03-10  2:34 ` [PATCH 1/3] tracing: Combine enum and arrays into single macro in " Steven Rostedt
2018-03-12 10:31   ` Masami Hiramatsu
2018-03-10  2:34 ` [PATCH 2/3] tracing: Clean up and document pred_funcs_##type creation and use Steven Rostedt
2018-03-12 13:42   ` Masami Hiramatsu
2018-03-10  2:34 ` [PATCH 3/3] tracing: Rewrite filter logic to be simpler and faster Steven Rostedt
2018-03-10  3:10   ` Steven Rostedt
2018-03-10  3:10     ` Steven Rostedt
2018-03-10  3:15     ` Steven Rostedt
2018-03-10  3:15       ` Steven Rostedt
2018-03-10  3:22       ` Steven Rostedt
2018-03-10  3:22         ` Steven Rostedt
2018-03-10  3:18   ` Steven Rostedt
2018-03-12 12:42   ` Jiri Olsa
2018-03-12 18:38     ` Steven Rostedt
2018-03-12 15:10   ` Jiri Olsa
2018-03-12 18:40     ` Steven Rostedt
2018-03-12 18:54       ` Jiri Olsa
2018-03-12 19:10         ` Steven Rostedt
2018-03-12 23:52         ` Steven Rostedt
2018-03-13 10:14           ` Jiri Olsa
2018-03-13 14:12             ` Steven Rostedt
2018-03-13 14:27               ` Jiri Olsa
2018-03-11 19:54 ` [PATCH 0/3] tracing: Rewrite the function filter code Jiri Olsa

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