On 5/25/20 11:35 AM, Jérôme 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@xxxxxxxxxx>
>> ---
>> 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/wireless.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
>
> Hello,
>
> This patch also solves a warning I encountered when I launched sparse
> (with make C=1):
>
> /usr/lib/gcc-cross/arm-linux-gnueabihf/9/include/stddef.h:406:9: warning: preprocessor token offsetof redefined
> ./include/linux/stddef.h:17:9: this was the original definition
>
> However, I wonder if it useful to keep 'include <stddef.h>' when this file
> is included from userspace. If it does not compile anymore, there is
> problem somewhere else, no?
>
> (Globally, I always find suspicious a kernel source that includes a system
> 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
./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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