dlfcn: Avoid one-element flexible array in Dl_serinfo
Commit Message
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.
Comments
* 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".)
@@ -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 */