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Re: [PATCH] dlfcn: Avoid one-element flexible array in Dl_serinfo
- From: Florian Weimer <fweimer at redhat dot com>
- To: libc-alpha at sourceware dot org
- Cc: Paul Eggert <eggert at cs dot ucla dot edu>
- Date: Tue, 18 Jun 2019 16:27:05 +0200
- Subject: Re: [PATCH] dlfcn: Avoid one-element flexible array in Dl_serinfo
- References: <87a7ey8ytd.fsf@oldenburg2.str.redhat.com>
* 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