Re: [Qemu-devel] [PATCH] scripts/qapi-types.py: Add dummy member to empty structs

[Eric Blake]

On 12/23/2014 11:24 AM, Peter Maydell wrote:
> Make sure that all generated C structs have at least one field; this
> avoids potential issues with attempting to malloc space for
> zero-length structs in C (g_malloc(sizeof struct) would return NULL).
> It also avoids an incompatibility with C++ (where an empty struct is
> size 1); that isn't important to us now but might be in future.
> 
> Generated empty structures look like this:
>     struct Abort
>     {
>         char qapi_dummy_field_for_empty_struct;
>     };
> 
> This silences clang warnings like:
> ./qapi-types.h:3752:1: warning: empty struct has size 0 in C, size 1 in C++ 
> [-Wextern-c-compat]
> struct Abort
> ^
> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  scripts/qapi-types.py | 8 ++++++++
>  1 file changed, 8 insertions(+)

Reviewed-by: Eric Blake <address@hidden>

However, I'm a bit surprised that there is no testsuite coverage for
this; it would be nice if we had at least one test that used an empty
struct to prove that we continue to generate them and their visitors
correctly.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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