On 03/16/16 17:50, Andrew Fish wrote:
>
>> On Mar 16, 2016, at 6:54 AM, Laszlo Ersek <[email protected]> wrote:
>>
>> On 03/14/16 16:38, Leif Lindholm wrote:
>>> To permit many existing platforms to build with -Wunused-parameter, on
>>> GCC and CLANG, the unused parameters need to be annotated as such.
>>> Existing regexp code already uses ARG_UNUSED for this, but it is really
>>> needed across the codebase - so add a version in Base.h.
>>>
>>> Contributed-under: TianoCore Contribution Agreement 1.0
>>> Signed-off-by: Leif Lindholm <[email protected]>
>>> ---
>>>
>>> This is really the result of a friendly toolchain engineer informing me
>>> CLANG has the -Weverything flag, to actually enable all possible
>>> warnings.
>>>
>>> One problem trying to pick out the real bugs from the just not entirely
>>> clear code is that basically a lot of *LibNull implementations, and
>>> some libraries that should be usable, trip build failures due to unused
>>> parameters.
>>>
>>> MdePkg/Include/Base.h | 9 +++++++++
>>> 1 file changed, 9 insertions(+)
>>>
>>> diff --git a/MdePkg/Include/Base.h b/MdePkg/Include/Base.h
>>> index 89b2aed..f789094 100644
>>> --- a/MdePkg/Include/Base.h
>>> +++ b/MdePkg/Include/Base.h
>>> @@ -189,6 +189,15 @@ struct _LIST_ENTRY {
>>> ///
>>> #define OPTIONAL
>>>
>>> +///
>>> +/// Function argument intentionally unused in function.
>>> +///
>>> +#if defined(__GNUC__) || defined(__clang__)
>>> + #define ARG_UNUSED __attribute__ ((unused))
>>> +#else
>>> + #define ARG_UNUSED
>>> +#endif
>>> +
>>> //
>>> // UEFI specification claims 1 and 0. We are concerned about the
>>> // complier portability so we did it this way.
>>>
>>
>> Support for this seems to go back to gcc-4.4:
>>
>> https://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/Variable-Attributes.html
>>
>> So it looks safe. (And I agree with the idea.)
>>
>
> I'm confused by the usage, or really when the compiler detects the
> warning?
>
> For example how is this going to work on public interfaces?
> Protocols, PPIs, or library class definitions? There is a single
> definition of the function, but multiple implementations. Some
> implementations may not use some arguments. But what arguments get
> used seems to be an implementation choice and not part of the API?
> Thus it seems like this macro is not going to enable changing
> compiler flags?
I think this attribute would be used in library instances and protocol
implementations. It would not be used in library class headers nor
protocol definitions.
Example:
/* included from library class hdr of protocol def hdr */
int f(int x);
/* code in library instance or protocol impl */
int f(int x __attribute__ ((unused)))
{
return 0;
}
int main(void)
{
return f(-2);
}
Compiles silently with
$ gcc -Wall -Wextra -ansi -pedantic -Werror -o x x.c
If I remove __attribute__ ((unused)), I get:
x.c:5:15: error: unused parameter 'x' [-Werror=unused-parameter]
int f(int x)
^
cc1: all warnings being treated as errors
Thanks
Laszlo
>
> Or am I just confused?
>
> Thanks,
>
> Andrew Fish
>
>
>> Acked-by: Laszlo Ersek <[email protected]>
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>
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