Re: [PATCH] KVM: x86: Fix C++ user API for structures with variable length arrays

[David Woodhouse]

On Thu, 2026-02-26 at 11:02 -0800, Kees Cook wrote:
> 
> > Also put the header fields into a struct_group() to provide (in C) a
> > separate struct (e.g 'struct kvm_msrs_hdr') without the trailing VLA.
> 
> Right, my only worry is if C++ would want those header structs too. In
> that case, you'd probably want to use a macro to include them (since not
> all compilers are supporting transparent struct members yet):
> 
> #define __kvm_msrs_hdr	\
> 	__u32 nmsrs; /* number of msrs in entries */	\
> 	__u32 pad
> 
> struct kvm_msrs_hdr {
> 	__kvm_msrs_hdr;
> };
> 
> struct kvm_msrs {
> 	__kvm_msrs_hdr;
> 	__DECLARE_FLEX_ARRAY(struct kvm_msr_entry, entries);
> };

Hm, does the struct_group() not also depend on the compiler supporting
anonymous struct members? Is there a distinction I'm missing?

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