* Re: [Xenomai] [Xenomai-git] Philippe Gerum : boilerplate: add offsetof() shorthand
[not found] <E1ZIZjP-0001py-FB@sd-51317.xenomai.org>
@ 2015-07-24 13:20 ` Gilles Chanteperdrix
2015-07-24 13:59 ` Philippe Gerum
0 siblings, 1 reply; 6+ messages in thread
From: Gilles Chanteperdrix @ 2015-07-24 13:20 UTC (permalink / raw)
To: xenomai
git repository hosting wrote:
> Module: xenomai-3
> Branch: next
> Commit: 2a584d6763c64f9e566b5f53094d57dd72688857
> URL:
> http://git.xenomai.org/?p=xenomai-3.git;a=commit;h=2a584d6763c64f9e566b5f53094d57dd72688857
>
> Author: Philippe Gerum <rpm@xenomai.org>
> Date: Thu Jul 23 19:13:29 2015 +0200
>
> boilerplate: add offsetof() shorthand
>
> ---
>
> include/boilerplate/compiler.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/include/boilerplate/compiler.h
> b/include/boilerplate/compiler.h
> index e27d165..876e004 100644
> --- a/include/boilerplate/compiler.h
> +++ b/include/boilerplate/compiler.h
> @@ -54,4 +54,8 @@
> #define __aligned(__n) __attribute__((aligned (__n)))
> #endif
>
> +#ifndef offsetof
> +#define offsetof(__type, __member) __builtin_offsetof(__type, __member)
> +#endif
offsetof should be defined by glibc headers. By adding a definition, you
risk a compiler warning about multiple definitions if someone uses the
proper glibc header.
--
Gilles.
https://click-hack.org
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xenomai] [Xenomai-git] Philippe Gerum : boilerplate: add offsetof() shorthand
2015-07-24 13:20 ` [Xenomai] [Xenomai-git] Philippe Gerum : boilerplate: add offsetof() shorthand Gilles Chanteperdrix
@ 2015-07-24 13:59 ` Philippe Gerum
2015-07-24 14:04 ` Gilles Chanteperdrix
0 siblings, 1 reply; 6+ messages in thread
From: Philippe Gerum @ 2015-07-24 13:59 UTC (permalink / raw)
To: Gilles Chanteperdrix, xenomai
On 07/24/2015 03:20 PM, Gilles Chanteperdrix wrote:
>
> git repository hosting wrote:
>> Module: xenomai-3
>> Branch: next
>> Commit: 2a584d6763c64f9e566b5f53094d57dd72688857
>> URL:
>> http://git.xenomai.org/?p=xenomai-3.git;a=commit;h=2a584d6763c64f9e566b5f53094d57dd72688857
>>
>> Author: Philippe Gerum <rpm@xenomai.org>
>> Date: Thu Jul 23 19:13:29 2015 +0200
>>
>> boilerplate: add offsetof() shorthand
>>
>> ---
>>
>> include/boilerplate/compiler.h | 4 ++++
>> 1 file changed, 4 insertions(+)
>>
>> diff --git a/include/boilerplate/compiler.h
>> b/include/boilerplate/compiler.h
>> index e27d165..876e004 100644
>> --- a/include/boilerplate/compiler.h
>> +++ b/include/boilerplate/compiler.h
>> @@ -54,4 +54,8 @@
>> #define __aligned(__n) __attribute__((aligned (__n)))
>> #endif
>>
>> +#ifndef offsetof
>> +#define offsetof(__type, __member) __builtin_offsetof(__type, __member)
>> +#endif
>
> offsetof should be defined by glibc headers. By adding a definition, you
> risk a compiler warning about multiple definitions if someone uses the
> proper glibc header.
>
>
There is hardly any risk of that kind when using the gcc builtin.
--
Philippe.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xenomai] [Xenomai-git] Philippe Gerum : boilerplate: add offsetof() shorthand
2015-07-24 13:59 ` Philippe Gerum
@ 2015-07-24 14:04 ` Gilles Chanteperdrix
2015-07-24 14:10 ` Philippe Gerum
0 siblings, 1 reply; 6+ messages in thread
From: Gilles Chanteperdrix @ 2015-07-24 14:04 UTC (permalink / raw)
To: Philippe Gerum; +Cc: xenomai
Philippe Gerum wrote:
> On 07/24/2015 03:20 PM, Gilles Chanteperdrix wrote:
>>
>> git repository hosting wrote:
>>> Module: xenomai-3
>>> Branch: next
>>> Commit: 2a584d6763c64f9e566b5f53094d57dd72688857
>>> URL:
>>> http://git.xenomai.org/?p=xenomai-3.git;a=commit;h=2a584d6763c64f9e566b5f53094d57dd72688857
>>>
>>> Author: Philippe Gerum <rpm@xenomai.org>
>>> Date: Thu Jul 23 19:13:29 2015 +0200
>>>
>>> boilerplate: add offsetof() shorthand
>>>
>>> ---
>>>
>>> include/boilerplate/compiler.h | 4 ++++
>>> 1 file changed, 4 insertions(+)
>>>
>>> diff --git a/include/boilerplate/compiler.h
>>> b/include/boilerplate/compiler.h
>>> index e27d165..876e004 100644
>>> --- a/include/boilerplate/compiler.h
>>> +++ b/include/boilerplate/compiler.h
>>> @@ -54,4 +54,8 @@
>>> #define __aligned(__n) __attribute__((aligned (__n)))
>>> #endif
>>>
>>> +#ifndef offsetof
>>> +#define offsetof(__type, __member) __builtin_offsetof(__type,
>>> __member)
>>> +#endif
>>
>> offsetof should be defined by glibc headers. By adding a definition, you
>> risk a compiler warning about multiple definitions if someone uses the
>> proper glibc header.
>>
>>
>
> There is hardly any risk of that kind when using the gcc builtin.
>
builtin or not, if I compile the following program:
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#define offsetof(__type, __member) __builtin_offsetof(__type,__member)
int main(void)
{
printf("Hello\n");
return EXIT_SUCCESS;
}
I get the following warning:
$ gcc -Wall -W -o foo foo.c
foo.c:5:0: warning: "offsetof" redefined [enabled by default]
#define offsetof(__type, __member) __builtin_offsetof(__type,__member)
^
In file included from /usr/include/alloca.h:24:0,
from /usr/include/stdlib.h:491,
from foo.c:3:
/usr/lib64/gcc/x86_64-slackware-linux/4.8.2/include/stddef.h:413:0: note:
this is the location of the previous definition
#define offsetof(TYPE, MEMBER) __builtin_offsetof (TYPE, MEMBER)
^
--
Gilles.
https://click-hack.org
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xenomai] [Xenomai-git] Philippe Gerum : boilerplate: add offsetof() shorthand
2015-07-24 14:04 ` Gilles Chanteperdrix
@ 2015-07-24 14:10 ` Philippe Gerum
2015-07-24 14:15 ` Gilles Chanteperdrix
0 siblings, 1 reply; 6+ messages in thread
From: Philippe Gerum @ 2015-07-24 14:10 UTC (permalink / raw)
To: Gilles Chanteperdrix; +Cc: xenomai
On 07/24/2015 04:04 PM, Gilles Chanteperdrix wrote:
>
> Philippe Gerum wrote:
>> On 07/24/2015 03:20 PM, Gilles Chanteperdrix wrote:
>>>
>>> git repository hosting wrote:
>>>> Module: xenomai-3
>>>> Branch: next
>>>> Commit: 2a584d6763c64f9e566b5f53094d57dd72688857
>>>> URL:
>>>> http://git.xenomai.org/?p=xenomai-3.git;a=commit;h=2a584d6763c64f9e566b5f53094d57dd72688857
>>>>
>>>> Author: Philippe Gerum <rpm@xenomai.org>
>>>> Date: Thu Jul 23 19:13:29 2015 +0200
>>>>
>>>> boilerplate: add offsetof() shorthand
>>>>
>>>> ---
>>>>
>>>> include/boilerplate/compiler.h | 4 ++++
>>>> 1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/include/boilerplate/compiler.h
>>>> b/include/boilerplate/compiler.h
>>>> index e27d165..876e004 100644
>>>> --- a/include/boilerplate/compiler.h
>>>> +++ b/include/boilerplate/compiler.h
>>>> @@ -54,4 +54,8 @@
>>>> #define __aligned(__n) __attribute__((aligned (__n)))
>>>> #endif
>>>>
>>>> +#ifndef offsetof
>>>> +#define offsetof(__type, __member) __builtin_offsetof(__type,
>>>> __member)
>>>> +#endif
>>>
>>> offsetof should be defined by glibc headers. By adding a definition, you
>>> risk a compiler warning about multiple definitions if someone uses the
>>> proper glibc header.
>>>
>>>
>>
>> There is hardly any risk of that kind when using the gcc builtin.
>>
>
> builtin or not, if I compile the following program:
>
> #include <stddef.h>
> #include <stdio.h>
> #include <stdlib.h>
>
> #define offsetof(__type, __member) __builtin_offsetof(__type,__member)
Your program is wrong in the first place, since offsetof() is defined by
stddef.h. Given that 3.x assumes a modern compiler with offsetof()
available from there, you are just asking for troubles, especially since
you explicitly omit the guard, which is not the best way to get things
working either.
What can be done is including stddef.h from compiler.h, and provide a
placeholder for offsetof() based on the null cast trick. That would make
more sense.
>
> int main(void)
> {
> printf("Hello\n");
> return EXIT_SUCCESS;
> }
>
> I get the following warning:
>
> $ gcc -Wall -W -o foo foo.c
> foo.c:5:0: warning: "offsetof" redefined [enabled by default]
> #define offsetof(__type, __member) __builtin_offsetof(__type,__member)
> ^
> In file included from /usr/include/alloca.h:24:0,
> from /usr/include/stdlib.h:491,
> from foo.c:3:
> /usr/lib64/gcc/x86_64-slackware-linux/4.8.2/include/stddef.h:413:0: note:
> this is the location of the previous definition
> #define offsetof(TYPE, MEMBER) __builtin_offsetof (TYPE, MEMBER)
> ^
>
>
--
Philippe.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xenomai] [Xenomai-git] Philippe Gerum : boilerplate: add offsetof() shorthand
2015-07-24 14:10 ` Philippe Gerum
@ 2015-07-24 14:15 ` Gilles Chanteperdrix
2015-07-24 14:25 ` Philippe Gerum
0 siblings, 1 reply; 6+ messages in thread
From: Gilles Chanteperdrix @ 2015-07-24 14:15 UTC (permalink / raw)
To: Philippe Gerum; +Cc: xenomai
Philippe Gerum wrote:
> On 07/24/2015 04:04 PM, Gilles Chanteperdrix wrote:
>>
>> Philippe Gerum wrote:
>>> On 07/24/2015 03:20 PM, Gilles Chanteperdrix wrote:
>>>>
>>>> git repository hosting wrote:
>>>>> Module: xenomai-3
>>>>> Branch: next
>>>>> Commit: 2a584d6763c64f9e566b5f53094d57dd72688857
>>>>> URL:
>>>>> http://git.xenomai.org/?p=xenomai-3.git;a=commit;h=2a584d6763c64f9e566b5f53094d57dd72688857
>>>>>
>>>>> Author: Philippe Gerum <rpm@xenomai.org>
>>>>> Date: Thu Jul 23 19:13:29 2015 +0200
>>>>>
>>>>> boilerplate: add offsetof() shorthand
>>>>>
>>>>> ---
>>>>>
>>>>> include/boilerplate/compiler.h | 4 ++++
>>>>> 1 file changed, 4 insertions(+)
>>>>>
>>>>> diff --git a/include/boilerplate/compiler.h
>>>>> b/include/boilerplate/compiler.h
>>>>> index e27d165..876e004 100644
>>>>> --- a/include/boilerplate/compiler.h
>>>>> +++ b/include/boilerplate/compiler.h
>>>>> @@ -54,4 +54,8 @@
>>>>> #define __aligned(__n) __attribute__((aligned (__n)))
>>>>> #endif
>>>>>
>>>>> +#ifndef offsetof
>>>>> +#define offsetof(__type, __member) __builtin_offsetof(__type,
>>>>> __member)
>>>>> +#endif
>>>>
>>>> offsetof should be defined by glibc headers. By adding a definition,
>>>> you
>>>> risk a compiler warning about multiple definitions if someone uses the
>>>> proper glibc header.
>>>>
>>>>
>>>
>>> There is hardly any risk of that kind when using the gcc builtin.
>>>
>>
>> builtin or not, if I compile the following program:
>>
>> #include <stddef.h>
>> #include <stdio.h>
>> #include <stdlib.h>
>>
>> #define offsetof(__type, __member) __builtin_offsetof(__type,__member)
>
>
> Your program is wrong in the first place, since offsetof() is defined by
> stddef.h. Given that 3.x assumes a modern compiler with offsetof()
> available from there, you are just asking for troubles, especially since
> you explicitly omit the guard, which is not the best way to get things
> working either.
I did that on purpose to illustrate the case that would happen if stddef
was included after compiler.h, because the compiler stddef.h does not
contain any guard. The guard in compiler.h does not work if compiler.h is
included first.
>
> What can be done is including stddef.h from compiler.h, and provide a
> placeholder for offsetof() based on the null cast trick. That would make
> more sense.
Not really, stddef.h has been defining offetof for ages.
--
Gilles.
https://click-hack.org
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xenomai] [Xenomai-git] Philippe Gerum : boilerplate: add offsetof() shorthand
2015-07-24 14:15 ` Gilles Chanteperdrix
@ 2015-07-24 14:25 ` Philippe Gerum
0 siblings, 0 replies; 6+ messages in thread
From: Philippe Gerum @ 2015-07-24 14:25 UTC (permalink / raw)
To: Gilles Chanteperdrix; +Cc: xenomai
On 07/24/2015 04:15 PM, Gilles Chanteperdrix wrote:
>
> Philippe Gerum wrote:
>> On 07/24/2015 04:04 PM, Gilles Chanteperdrix wrote:
>>>
>>> Philippe Gerum wrote:
>>>> On 07/24/2015 03:20 PM, Gilles Chanteperdrix wrote:
>>>>>
>>>>> git repository hosting wrote:
>>>>>> Module: xenomai-3
>>>>>> Branch: next
>>>>>> Commit: 2a584d6763c64f9e566b5f53094d57dd72688857
>>>>>> URL:
>>>>>> http://git.xenomai.org/?p=xenomai-3.git;a=commit;h=2a584d6763c64f9e566b5f53094d57dd72688857
>>>>>>
>>>>>> Author: Philippe Gerum <rpm@xenomai.org>
>>>>>> Date: Thu Jul 23 19:13:29 2015 +0200
>>>>>>
>>>>>> boilerplate: add offsetof() shorthand
>>>>>>
>>>>>> ---
>>>>>>
>>>>>> include/boilerplate/compiler.h | 4 ++++
>>>>>> 1 file changed, 4 insertions(+)
>>>>>>
>>>>>> diff --git a/include/boilerplate/compiler.h
>>>>>> b/include/boilerplate/compiler.h
>>>>>> index e27d165..876e004 100644
>>>>>> --- a/include/boilerplate/compiler.h
>>>>>> +++ b/include/boilerplate/compiler.h
>>>>>> @@ -54,4 +54,8 @@
>>>>>> #define __aligned(__n) __attribute__((aligned (__n)))
>>>>>> #endif
>>>>>>
>>>>>> +#ifndef offsetof
>>>>>> +#define offsetof(__type, __member) __builtin_offsetof(__type,
>>>>>> __member)
>>>>>> +#endif
>>>>>
>>>>> offsetof should be defined by glibc headers. By adding a definition,
>>>>> you
>>>>> risk a compiler warning about multiple definitions if someone uses the
>>>>> proper glibc header.
>>>>>
>>>>>
>>>>
>>>> There is hardly any risk of that kind when using the gcc builtin.
>>>>
>>>
>>> builtin or not, if I compile the following program:
>>>
>>> #include <stddef.h>
>>> #include <stdio.h>
>>> #include <stdlib.h>
>>>
>>> #define offsetof(__type, __member) __builtin_offsetof(__type,__member)
>>
>>
>> Your program is wrong in the first place, since offsetof() is defined by
>> stddef.h. Given that 3.x assumes a modern compiler with offsetof()
>> available from there, you are just asking for troubles, especially since
>> you explicitly omit the guard, which is not the best way to get things
>> working either.
>
> I did that on purpose to illustrate the case that would happen if stddef
> was included after compiler.h, because the compiler stddef.h does not
> contain any guard. The guard in compiler.h does not work if compiler.h is
> included first.
>
>>
>> What can be done is including stddef.h from compiler.h, and provide a
>> placeholder for offsetof() based on the null cast trick. That would make
>> more sense.
>
> Not really, stddef.h has been defining offetof for ages.
>
>
>
That is not the point, including stddef.h first in compiler.h before
trying the fallback definition would prevent the issue you mentioned a
sentence above. Whether the fallback implementation would ever be picked
or not due to stddef.h defining offsetof() most of the time is not
really an urgent issue.
--
Philippe.
^ permalink raw reply [flat|nested] 6+ messages in thread
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[not found] <E1ZIZjP-0001py-FB@sd-51317.xenomai.org>
2015-07-24 13:20 ` [Xenomai] [Xenomai-git] Philippe Gerum : boilerplate: add offsetof() shorthand Gilles Chanteperdrix
2015-07-24 13:59 ` Philippe Gerum
2015-07-24 14:04 ` Gilles Chanteperdrix
2015-07-24 14:10 ` Philippe Gerum
2015-07-24 14:15 ` Gilles Chanteperdrix
2015-07-24 14:25 ` Philippe Gerum
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