[PATCH] wireless: Use linux/stddef.h instead of stddef.h

[PATCH] wireless: Use linux/stddef.h instead of stddef.h

[Hauke Mehrtens]

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/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
 
 /***************************** VERSION *****************************/
 /*
-- 
2.20.1

Re: [PATCH] wireless: Use linux/stddef.h instead of stddef.h

[Jérôme Pouiller]

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/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)


-- 
Jérôme Pouiller

Re: [PATCH] wireless: Use linux/stddef.h instead of stddef.h

[Hauke Mehrtens]

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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@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/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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Re: [PATCH] wireless: Use linux/stddef.h instead of stddef.h

[Jérôme Pouiller]

On Tuesday 26 May 2020 23:02:56 CEST Hauke Mehrtens wrote:
> 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@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/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.

In this case, maybe the problem should be resolved directly in
uapi/linux/stddef.h?

I have found other headers that use offsetof and may have the same problem
(currently, they do not include stddef.h. So, some of the macros do not
compile):
   - include/uapi/linux/fuse.h
   - include/uapi/linux/genwqe/genwqe_card.h
   - include/uapi/linux/gfs2_ondisk.h

-- 
Jérôme Pouiller

Re: [PATCH] wireless: Use linux/stddef.h instead of stddef.h

[Hauke Mehrtens]

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On 5/27/20 4:03 PM, Jérôme Pouiller wrote:
> On Tuesday 26 May 2020 23:02:56 CEST Hauke Mehrtens wrote:
>> 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@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/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.
> 
> In this case, maybe the problem should be resolved directly in
> uapi/linux/stddef.h?
> 
> I have found other headers that use offsetof and may have the same problem
> (currently, they do not include stddef.h. So, some of the macros do not
> compile):
>    - include/uapi/linux/fuse.h
>    - include/uapi/linux/genwqe/genwqe_card.h
>    - include/uapi/linux/gfs2_ondisk.h
> 
Hi,

Would you prefer to add this to include/uapi/linux/stddef.h:
#ifndef offsetof
#define offsetof(TYPE, MEMBER)	((size_t)&((TYPE *)0)->MEMBER)
#endif

and then include linux/stddef.h in all header files which use offsetof?

include/uapi/linux/fuse.h checks for __KERNEL__ and then includes
linux/types.h or stdint.h, my initial approach would be to do this in a
similar way for stddef.h.


What is the kernel policy of including system header files like stddef.h?

Hauke


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