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Subject: Re: [PATCH] wireless: Use linux/stddef.h instead of stddef.h
To:     =?UTF-8?B?SsOpcsO0bWUgUG91aWxsZXI=?= <jerome.pouiller@silabs.com>
Cc:     johannes.berg@intel.com, ndesaulniers@google.com,
        pihsun@chromium.org, linux-wireless@vger.kernel.org
References: <20200521201422.16493-1-hauke@hauke-m.de>
 <2555103.LUZAIfNjjX@pc-42>
From:   Hauke Mehrtens <hauke@hauke-m.de>
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Message-ID: <d2db65dc-527b-b9a7-45a6-82a4df9cb732@hauke-m.de>
Date:   Tue, 26 May 2020 23:02:56 +0200
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On 5/25/20 11:35 AM, J=C3=A9r=C3=B4me Pouiller wrote:
> On Thursday 21 May 2020 22:14:22 CEST Hauke Mehrtens wrote:
>> When compiling inside the kernel include linux/stddef.h instead of
>> stddef.h. When I compile this header file in backports for power PC I
>> run into a conflict with ptrdiff_t. I was unable to reproduce this in
>> mainline kernel. I still would like to fix this problem in the kernel.=

>>
>> Fixes: 6989310f5d43 ("wireless: Use offsetof instead of custom macro."=
)
>> Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
>> ---
>>  include/uapi/linux/wireless.h | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/uapi/linux/wireless.h b/include/uapi/linux/wirele=
ss.h
>> index a2c006a364e0..24f3371ad826 100644
>> --- a/include/uapi/linux/wireless.h
>> +++ b/include/uapi/linux/wireless.h
>> @@ -74,7 +74,11 @@
>>  #include <linux/socket.h>              /* for "struct sockaddr" et al=
  */
>>  #include <linux/if.h>                  /* for IFNAMSIZ and co... */
>>
>> -#include <stddef.h>                     /* for offsetof */
>> +#ifdef __KERNEL__
>> +#      include <linux/stddef.h>        /* for offsetof */
>> +#else
>> +#      include <stddef.h>              /* for offsetof */
>> +#endif
>=20
> Hello,
>=20
> This patch also solves a warning I encountered when I launched sparse
> (with make C=3D1):
>=20
>   /usr/lib/gcc-cross/arm-linux-gnueabihf/9/include/stddef.h:406:9: warn=
ing: preprocessor token offsetof redefined
>   ./include/linux/stddef.h:17:9: this was the original definition
>=20
> However, I wonder if it useful to keep 'include <stddef.h>' when this f=
ile
> is included from userspace. If it does not compile anymore, there is
> problem somewhere else, no?
>=20
> (Globally, I always find suspicious a kernel source that includes a sys=
tem
> header)
Hi,

The wireless.h makes use of offsetof and this is defined in system
stddef.h and in include/linux/stddef.h. When we only include
linux/stddef.h it will work fine when compiled inside the kernel, but it
could cause problems when used in user space, because this would include
=2E/include/uapi/linux/stddef.h which does not define offsetof.

I think we need the #ifdef __KERNEL__ to make this work in the kernel
and in the user space.

Hauke


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