On Tue, Aug 23, 2022 at 04:15:54PM +0200, Peter Krempa wrote:
> The most recent environment e.g. present in our Fedora Rawhide builds
> fail to build the tree with clang with the following error:
>
> ../src/util/virhostcpu.c:1291:25: error: field 'header' with variable sized type 'struct kvm_msrs' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
> struct kvm_msrs header;
> ^
>
> The problem seems to be that clang doesn't like the new way the
> 'entries' field in struct kvm_msrs is declared.
>
> To work around the issue we can simply allocate the variable dynamically
> and use the 'entries' member as it was intended to to access the
> members.
We explicitly only support GCC and CLang, and intentionally rely on
many GNU extensions to C. CLang is trying to be helpful to people
who need fully portable C code, but we don't care about that. So
why not just turn off the warning by adding
-Wno-gnu-variable-sized-style-not-at-end
better than making our code less understandable IMHO
>
> Signed-off-by: Peter Krempa <pkrempa@xxxxxxxxxx>
> ---
> src/util/virhostcpu.c | 15 ++++++---------
> 1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/src/util/virhostcpu.c b/src/util/virhostcpu.c
> index 54d0166b85..c1e8dc8078 100644
> --- a/src/util/virhostcpu.c
> +++ b/src/util/virhostcpu.c
> @@ -1287,25 +1287,22 @@ virHostCPUGetMSRFromKVM(unsigned long index,
> uint64_t *result)
> {
> VIR_AUTOCLOSE fd = -1;
> - struct {
> - struct kvm_msrs header;
> - struct kvm_msr_entry entry;
> - } msr = {
> - .header = { .nmsrs = 1 },
> - .entry = { .index = index },
> - };
> + g_autofree struct kvm_msrs *msr = g_malloc0(sizeof(struct kvm_msrs) +
> + sizeof(struct kvm_msr_entry));
> + msr->nmsrs = 1;
> + msr->entries[0].index = index;
>
> if ((fd = open(KVM_DEVICE, O_RDONLY)) < 0) {
> virReportSystemError(errno, _("Unable to open %s"), KVM_DEVICE);
> return -1;
> }
>
> - if (ioctl(fd, KVM_GET_MSRS, &msr) < 0) {
> + if (ioctl(fd, KVM_GET_MSRS, msr) < 0) {
> VIR_DEBUG("Cannot get MSR 0x%lx from KVM", index);
> return 1;
> }
>
> - *result = msr.entry.data;
> + *result = msr->entries[0].data;
> return 0;
> }
>
> --
> 2.37.1
>
With regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
