dlfcn: Avoid one-element flexible array in Dl_serinfo

  The dls_serpath path field, as an array of length 1, introduces
unexpected array subscript checks with some compilers.

GCC versions before 3.0 treat the nested anonymous union as a
declaration of an unnamed type, and not as a member declaration,
so this construct cannot be used for these compilers.

2019-06-03  Florian Weimer  <fweimer@redhat.com>

	[BZ #24166]
	* dlfcn/dlfcn.h (Dl_serinfo): Do not use array of length 1 for
	dls_serpath field.
  

* Florian Weimer:

> The dls_serpath path field, as an array of length 1, introduces
> unexpected array subscript checks with some compilers.
>
> GCC versions before 3.0 treat the nested anonymous union as a
> declaration of an unnamed type, and not as a member declaration,
> so this construct cannot be used for these compilers.
>
> 2019-06-03  Florian Weimer  <fweimer@redhat.com>
>
> 	[BZ #24166]
> 	* dlfcn/dlfcn.h (Dl_serinfo): Do not use array of length 1 for
> 	dls_serpath field.
>
> diff --git a/dlfcn/dlfcn.h b/dlfcn/dlfcn.h
> index 896ad6fc9b..c550371999 100644
> --- a/dlfcn/dlfcn.h
> +++ b/dlfcn/dlfcn.h
> @@ -180,7 +180,19 @@ typedef struct
>  {
>    size_t dls_size;		/* Size in bytes of the whole buffer.  */
>    unsigned int dls_cnt;		/* Number of elements in `dls_serpath'.  */
> +# if __GNUC_PREREQ (3, 0)
> +  /* The zero-length array avoids an unwanted array subscript check by
> +     the compiler, while the surrounding anonymous union preserves the
> +     historic size of the type.  At the time of writing, GNU C does
> +     not support structs with flexible array members in unions.  */
> +  __extension__ union
> +  {
> +    Dl_serpath dls_serpath[0]; /* Actually longer, dls_cnt elements.  */
> +    Dl_serpath __dls_serpath_pad[1];
> +  };
> +# else
>    Dl_serpath dls_serpath[1];	/* Actually longer, dls_cnt elements.  */
> +# endif
>  } Dl_serinfo;
>  #endif /* __USE_GNU */
>  

Ping?

Thanks,
Florian
  

That looks OK to me, thanks. (Sorry, I thought I had already said "LGTM".)