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Date:   Thu, 31 Aug 2017 12:16:53 +1000
From:   Michael Ellerman <>
To:     Joe Stringer <>,
        Andrew Morton <>
Cc:     LKML <>,
        Ian Abbott <>, Arnd Bergmann <>,
        Michal Nazarewicz <>,
        Kees Cook <>
Subject: Re: [PATCH] compiler: Don't perform compiletime_assert with -O0.

Joe Stringer <> writes:

> On 30 August 2017 at 15:59, Andrew Morton <> wrote:
>> On Tue, 29 Aug 2017 16:01:14 -0700 Joe Stringer <> 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


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