Re: [PATCH v2 2/6] configure: avoid new clang 11+ warnings

[Thomas Huth]

On 26/10/2020 16.12, Paolo Bonzini wrote:
> On 26/10/20 16:03, Daniele Buono wrote:
>> Hi Paolo,
>> I reorganized UASStatus to put uas_iu at the end and it works fine.
>> Unfortunately, this uncovered another part of the code with a similar
>> issue (variable sized type not at the end of the struct), here:
>>
>> In file included from ../qemu-cfi-v3/target/s390x/diag.c:21:
>> ../qemu-cfi-v3/hw/s390x/ipl.h:161:23: error: field 'iplb' with variable
>> sized type 'IplParameterBlock' (aka 'union IplParameterBlock') not at
>> the end of a struct or class is a GNU extension
>> [-Werror,-Wgnu-variable-sized-type-not-at-end]
>>     IplParameterBlock iplb;
>>                       ^
>> ../qemu-cfi-v3/hw/s390x/ipl.h:162:23: error: field 'iplb_pv' with
>> variable sized type 'IplParameterBlock' (aka 'union IplParameterBlock')
>> not at the end of a struct or class is a GNU extension
>> [-Werror,-Wgnu-variable-sized-type-not-at-end]
>>     IplParameterBlock iplb_pv;
>>
>> My understanding is that each of these IplParameterBlock may contain
>> either a IPLBlockPV or a IplBlockFcp, which both end with a variable
>> sized field (an array).
>>
>> Adding maintainers of s390x to see if they have a suggested solution to
>> avoid disabling the warning.
> 
> This one seems okay because the union constrains the size to 4K. If
> "[0]" is enough to shut up the compiler, I'd say do that.

The "IplBlockFcp fcp" part seems to be completely unused, so I think you
could even remove that IplBlockFcp struct. For IPLBlockPV I agree with
Paolo, it's likely easiest to use [0] for that struct.

 Thomas