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From: Jan Beich <jbeich@FreeBSD.org>
To: Hans Petter Selasky <hps@selasky.org>
Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org,
 src-committers@freebsd.org
Subject: Re: svn commit: r329371 - head/sys/compat/linuxkpi/common/include/asm
References: <201802161520.w1GFKLiA049085@repo.freebsd.org>
 <mv08-30rc-wny@FreeBSD.org>
 <6f790c90-8c65-ab0b-4a58-2814be55f09f@selasky.org>
Date: Sat, 17 Feb 2018 10:33:40 +0100
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Hans Petter Selasky <hps@selasky.org> writes:

> On 02/17/18 01:42, Jan Beich wrote:
>
>> Hans Petter Selasky <hselasky@FreeBSD.org> writes:
>>
>>> Author: hselasky
>>> Date: Fri Feb 16 15:20:21 2018
>>> New Revision: 329371
>>> URL: https://svnweb.freebsd.org/changeset/base/329371
>>>
>>> Log:
>>>    Allow the cmpxchg() macro in the LinuxKPI to work on pointers without
>>>    generating compiler warnings, -Wint-conversion .
>> [...]
>>
>> To generate errors instead ?
>>
>> $ make clean all -C /usr/ports/graphics/drm-next-kmod
>> [...]
>> drm_lock.c:72:10: error: flexible array member 'u8' in a union is not allowed
>>                  prev = cmpxchg(lock, old, new);
>>                         ^
>
> I believe this is a regression issue in GCC:
>
> https://gcc.gnu.org/ml/gcc-patches/2016-07/msg01505.html

If you didn't notice that bug is for C++, not C. GCC and Clang accept
flexible array members in unions only in C++. cmpxchg() from linuxkpi
doesn't seem to be used anywhere in the tree. If the macro didn't expand
there's nothing to produce an error for.

Anyway, I confirm r329447 fixed graphics/drm-next-kmod build.