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

[Cornelia Huck]

On Tue, 27 Oct 2020 12:26:21 +0100
Thomas Huth <thuth@redhat.com> wrote:

> 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.

The fcp block had probably been added for completeness' sake, but we do
not support list-directed IPL anyway. Not sure if we actually want it,
as we use a different mechanism for IPLing from SCSI devices. So yes,
maybe we should just drop it.