Re: [PATCH] x86/header: Use __DECLARE_FLEX_ARRAY() for struct setup_data flex array

[H. Peter Anvin]

On September 1, 2026 4:42:39 AM PDT, Federico Parola <fparola@xxxxxxxxx> wrote:
>After the `data` member of struct setup_data was switched to a flex
>array by commit 94dfc73e7cf4 ("treewide: uapi: Replace zero-length
>arrays with flexible-array members"), the struct can no longer be used
>as a header in a larger struct in C++, with errors like:
> flexible array member ‘setup_data::data’ not at end of ‘struct ...’
>This breaks compilation of our userspace code which imports the header
>in a C++ project.
>
>Similar to commit 2619da73bb2f ("KVM: x86: Use __DECLARE_FLEX_ARRAY()
>for UAPI structures with VLAs"), declare the member with
>__DECLARE_FLEX_ARRAY(), which uses [0] for C++ compilation.
>
>Fixes: 94dfc73e7cf4 ("treewide: uapi: Replace zero-length arrays with flexible-array members")
>Signed-off-by: Federico Parola <fparola@xxxxxxxxx>
>---
> arch/x86/include/uapi/asm/setup_data.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/arch/x86/include/uapi/asm/setup_data.h b/arch/x86/include/uapi/asm/setup_data.h
>index 2671c4e1b3a0b..afe1e3a2a6564 100644
>--- a/arch/x86/include/uapi/asm/setup_data.h
>+++ b/arch/x86/include/uapi/asm/setup_data.h
>@@ -28,7 +28,7 @@ struct setup_data {
> 	__u64 next;
> 	__u32 type;
> 	__u32 len;
>-	__u8 data[];
>+	__DECLARE_FLEX_ARRAY(__u8, data);
> };
> 
> /* extensible setup indirect data node */

Can we do this in the postprocessing of uapi headers, please?