On Fri, Sep 09 2022, Chenyi Qiang <chenyi.qi...@intel.com> wrote:
> In recent linux headers update to v6.0-rc, it switched GNU
Maybe
"A Linux headers update to v6.0-rc switches some definitions from the
GNU..."
?
> 'zero-length-array' extension to the C-standard-defined flexible array
> member. e.g.
>
> struct kvm_msrs {
> __u32 nmsrs; /* number of msrs in entries */
> __u32 pad;
>
> - struct kvm_msr_entry entries[0];
> + struct kvm_msr_entry entries[];
> };
>
> Those (unlike the GNU zero-length-array) have some extra restrictions like
> 'this must be put at the end of a struct', which clang build would complain
> about. e.g. the current code
>
> struct {
> struct kvm_msrs info;
> struct kvm_msr_entry entries[1];
> } msr_data = { }
>
> generates the warning like:
>
> target/i386/kvm/kvm.c:2868:25: error: field 'info' 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 info;
> ^
> In fact, the variable length 'entries[]' field in 'info' is zero-sized in
> GNU defined semantics, which can give predictable offset for 'entries[1]'
> in local msr_data. The local defined struct is just there to force a stack
> allocation large enough for 1 kvm_msr_entry, a clever trick but requires to
> turn off this clang warning.
>
> Suggested-by: Daniel P. Berrangé <berra...@redhat.com>
> Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
> Signed-off-by: Chenyi Qiang <chenyi.qi...@intel.com>
> ---
> configure | 1 +
> 1 file changed, 1 insertion(+)
Reviewed-by: Cornelia Huck <coh...@redhat.com>
