On 08.06.2023 14:18, Roberto Bagnara wrote:
> On 07/06/23 09:39, Jan Beulich wrote:
>> On 05.06.2023 15:26, Roberto Bagnara wrote:
>>> On 05/06/23 11:28, Jan Beulich wrote:
>>>> On 05.06.2023 07:28, Roberto Bagnara wrote:
>>> You are right: here are a few examples for U2:
>>>
>>> xen/arch/arm/cpuerrata.c:92.12-92.35:
>>> empty initializer list (ill-formed for the C99 standard, ISO/IEC 9899:1999
>>> Section 6.7.8: "An empty initialization list." [STD.emptinit]). Tool used
>>> is `/usr/bin/aarch64-linux-gnu-gcc-12'
>>> xen/include/xen/spinlock.h:31.21-31.23: expanded from macro `_LOCK_DEBUG'
>>> xen/include/xen/spinlock.h:143.57-143.67: expanded from macro
>>> `SPIN_LOCK_UNLOCKED'
>>> xen/include/xen/spinlock.h:144.43-144.60: expanded from macro
>>> `DEFINE_SPINLOCK'
>>
>> I'm afraid this is a bad example, as it goes hand-in-hand with using
>> another extension. I don't think using a non-empty initialization list
>> is going to work with
>>
>> union lock_debug { };
>
> Yes, this is C99 undefined behavior 58:
> "A structure or union is defined as containing no named members (6.7.2.1)."
>
> Here is another example:
>
> lpae_t pte = {};
>
> whereas we have
>
> typedef union {
> uint64_t bits;
> lpae_pt_t pt;
> lpae_p2m_t p2m;
> lpae_walk_t walk;
> } lpae_t;
>
>
>>> xen/arch/arm/cpuerrata.c:678.5-678.6:
>>> empty initializer list (ill-formed for the C99 standard, ISO/IEC 9899:1999
>>> Section 6.7.8: "An empty initialization list." [STD.emptinit]). Tool used
>>> is `/usr/bin/aarch64-linux-gnu-gcc-12'
>>>
>>> xen/arch/arm/cpufeature.c:33.5-33.6:
>>> empty initializer list (ill-formed for the C99 standard, ISO/IEC 9899:1999
>>> Section 6.7.8: "An empty initialization list." [STD.emptinit]). Tool used
>>> is `/usr/bin/aarch64-linux-gnu-gcc-12'
>>
>> Both of these are a common idiom we use: The "sentinel" of an array
>> of compound type initializer.
>
> Wouldn't it be possible writing such sentinels in a standard-compliant
> way, like {0} or similar, instead of {}?
I would be possible, sure, but the question is whether we want that. Iirc
in review comments we've been asking to preferably use {}, for being
shorter / less clutter without resulting in any ambiguity.
>>>>> U6) Empty declarations.
>>>
>>> Examples:
>>>
>>> xen/arch/arm/arm64/lib/find_next_bit.c:57.29:
>>> empty declaration (ill-formed for the C99 standard, ISO/IEC 9899:1999
>>> Section 6.7: "An empty declaration." [STD.emptdecl]). Tool used is
>>> `/usr/bin/aarch64-linux-gnu-gcc-12'
>>>
>>> xen/arch/arm/arm64/lib/find_next_bit.c:103.34:
>>> empty declaration (ill-formed for the C99 standard, ISO/IEC 9899:1999
>>> Section 6.7: "An empty declaration." [STD.emptdecl]). Tool used is
>>> `/usr/bin/aarch64-linux-gnu-gcc-12'
>>
>> Looks like these could be taken care of by finally purging our
>> EXPORT_SYMBOL() stub.
>>
>>> xen/arch/arm/include/asm/vreg.h:143.26:
>>> empty declaration (ill-formed for the C99 standard, ISO/IEC 9899:1999
>>> Section 6.7: "An empty declaration." [STD.emptdecl]). Tool used is
>>> `/usr/bin/aarch64-linux-gnu-gcc-12'
>>>
>>> xen/arch/arm/include/asm/vreg.h:144.26:
>>> empty declaration (ill-formed for the C99 standard, ISO/IEC 9899:1999
>>> Section 6.7: "An empty declaration." [STD.emptdecl]). Tool used is
>>> `/usr/bin/aarch64-linux-gnu-gcc-12'
>>
>> I'm having trouble spotting anything suspicious there.
>
> The macro expands to definitions of inline functions
> and after the macro invocation there is a ";".
>
> The preprocessed code is then:
>
> static inline void foo() { ... }
> ;
>
> where the final ";" is an empty declaration not allowed by
> the C99 language standard.
Oh, I see.
> Removing the ";" after the macro invocation is a possible solution,
> but other possibilities exist if this is strongly unwanted.
We have other macros to instantiate functions, and there no stray
semicolons are used. I think this wants doing the same way here, but it
being Arm code the ultimate say is with the Arm maintainers.
Jan
