All of lore.kernel.org
 help / color / mirror / Atom feed
From: Joe Stringer <joe@ovn.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Ian Abbott <abbotti@mev.co.uk>, Arnd Bergmann <arnd@arndb.de>,
	Michal Nazarewicz <mina86@mina86.com>,
	Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH] compiler: Don't perform compiletime_assert with -O0.
Date: Wed, 30 Aug 2017 23:52:39 -0700	[thread overview]
Message-ID: <CAPWQB7E_5jx+f8Z9d-1uqGdGEamskfUufKi62x-YZeG2TdBH7w@mail.gmail.com> (raw)
In-Reply-To: <878ti08oru.fsf@concordia.ellerman.id.au>

On 30 August 2017 at 19:16, Michael Ellerman <mpe@ellerman.id.au> wrote:
> Joe Stringer <joe@ovn.org> writes:
>
>> On 30 August 2017 at 15:59, Andrew Morton <akpm@linux-foundation.org> wrote:
>>> On Tue, 29 Aug 2017 16:01:14 -0700 Joe Stringer <joe@ovn.org> wrote:
>>>
>>>> Recent changes[0] to make use of __compiletime_assert() from
>>>> container_of() increased the usage of this macro, allowing developers to
>>>> notice type conflicts in usage of container_of() at compile time.
>>>> However, the implementation of __compiletime_assert relies on compiler
>>>> optimizations to report an error. This means that if a developer uses
>>>> "-O0" with any code that performs container_of(), the compiler will
>>>> always report an error regardless of whether there is an actual problem
>>>> in the code.
>>>>
>>>> This patch disables compile_time_assert when optimizations are disabled
>>>> to allow such code to compile with CFLAGS="-O0".
>>>
>>> I'm wondering if we should backport this into -stable.  Probably not,
>>> as I doubt if many people use -O0 - it's a pretty weird thing to do.  I
>>> used to use it a bit because it makes the ".lst" files (intermingled .c
>>> and .s files) make more sense.  In fact I'm wondering how you even
>>> noticed this?
>>
>> Local debugging, was trying to get a better understanding of the
>> underlying assembly and the code I was using just happened to use
>> container_of().
>
> Does the kernel actually build with -O0? I didn't think it actually
> worked.

I haven't tried the whole kernel, but you can set these CFLAGS on
specific files with a one-liner in a makefile:

CFLAGS_foo.o = -O0

      reply	other threads:[~2017-08-31  6:53 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-29 23:01 Joe Stringer
2017-08-30 10:26 ` Michal Nazarewicz
2017-08-30 18:03   ` Joe Stringer
2017-08-30 22:59 ` Andrew Morton
2017-08-30 23:22   ` Joe Stringer
2017-08-31  2:16     ` Michael Ellerman
2017-08-31  6:52       ` Joe Stringer [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAPWQB7E_5jx+f8Z9d-1uqGdGEamskfUufKi62x-YZeG2TdBH7w@mail.gmail.com \
    --to=joe@ovn.org \
    --cc=abbotti@mev.co.uk \
    --cc=akpm@linux-foundation.org \
    --cc=arnd@arndb.de \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mina86@mina86.com \
    --cc=mpe@ellerman.id.au \
    --subject='Re: [PATCH] compiler: Don'\''t perform compiletime_assert with -O0.' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.