Re: [musl] [PATCHv2] uapi libc compat: add fallback for unsupported libcs

Hauke Mehrtens
2017-07-08T21:14:33Z

On 07/08/2017 10:27 PM, Felix Janda wrote:
> libc-compat.h aims to prevent symbol collisions between uapi and libc
> headers for each supported libc. This requires continuous coordination
> between them.
>
> The goal of this commit is to improve the situation for libcs (such as
> musl) which are not yet supported and/or do not wish to be explicitly
> supported, while not affecting supported libcs. More precisely, with
> this commit, unsupported libcs can request the suppression of any
> specific uapi definition by defining the correspondings _UAPI_DEF_*
> macro as 0. This can fix symbol collisions for them, as long as the
> libc headers are included before the uapi headers. Inclusion in the
> other order is outside the scope of this commit.
>
> All infrastructure in order to enable this fallback for unsupported
> libcs is already in place, except that libc-compat.h unconditionally
> defines all _UAPI_DEF_* macros to 1 for all unsupported libcs so that
> any previous definitions are ignored. In order to fix this, this commit
> merely makes these definitions conditional.
>
> This commit together with the musl libc commit
>
> http://git.musl-libc.org/cgit/musl/commit/?id=04983f2272382af92eb8f8838964ff944fbb8258
>
> fixes for example the following compiler errors when <linux/in6.h> is
> included after musl's <netinet/in.h>:
>
> ./linux/in6.h:32:8: error: redefinition of 'struct in6_addr'
> ./linux/in6.h:49:8: error: redefinition of 'struct sockaddr_in6'
> ./linux/in6.h:59:8: error: redefinition of 'struct ipv6_mreq'
>
> Signed-off-by: Felix Janda <felix.janda-1KBjaw7Xf1+zQB+pC5nmwQ@public.gmane.org>
> Acked-by: Rich Felker <dalias-8zAoT0mYgF4@public.gmane.org>
> ---
> v2: The only change to the previous version is the commit title and
> message.
> ---
> include/uapi/linux/libc-compat.h | 52 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 52 insertions(+)

Does the documentation at the top of this file need some updates?

> diff --git a/include/uapi/linux/libc-compat.h b/include/uapi/linux/libc-compat.h
> index 44b8a6b..c316725 100644
> --- a/include/uapi/linux/libc-compat.h
> +++ b/include/uapi/linux/libc-compat.h
> @@ -171,42 +171,94 @@
> #else /* !defined(__GLIBC__) */

Why don't you used #ifndef ?

> /* Definitions for if.h */
> +#if !defined(__UAPI_DEF_IF_IFCONF)
> #define __UAPI_DEF_IF_IFCONF 1
> +#endif
> +#if !defined(__UAPI_DEF_IF_IFMAP)
> #define __UAPI_DEF_IF_IFMAP 1
> +#endif
> +#if !defined(__UAPI_DEF_IFNAMSIZ)

This should be:
#if !defined( __UAPI_DEF_IF_IFNAMSIZ)

> #define __UAPI_DEF_IF_IFNAMSIZ 1
> +#endif
> +#if !defined(__UAPI_DEF_IFREQ)

This should be:
#if !defined(__UAPI_DEF_IF_IFREQ)

> #define __UAPI_DEF_IF_IFREQ 1
> +#endif
> /* Everything up to IFF_DYNAMIC, matches net/if.h until glibc 2.23 */
> +#if !defined(__UAPI_DEF_IF_NET_DEVICE_FLAGS)
> #define __UAPI_DEF_IF_NET_DEVICE_FLAGS 1
> +#endif
> /* For the future if glibc adds IFF_LOWER_UP, IFF_DORMANT and IFF_ECHO */
> +#if !defined(__UAPI_DEF_IF_NET_DEVICE_FLAGS_LOWER_UP_DORMANT_ECHO)
> #define __UAPI_DEF_IF_NET_DEVICE_FLAGS_LOWER_UP_DORMANT_ECHO 1
> +#endif
>
> /* Definitions for in.h */
> +#if !defined(__UAPI_DEF_IN_ADDR)
> #define __UAPI_DEF_IN_ADDR 1
> +#endif
> +#if !defined(__UAPI_DEF_IN_IPPROTO)
> #define __UAPI_DEF_IN_IPPROTO 1
> +#endif
> +#if !defined(__UAPI_DEF_IN_PKTINFO)
> #define __UAPI_DEF_IN_PKTINFO 1
> +#endif
> +#if !defined(__UAPI_DEF_IP_MREQ)
> #define __UAPI_DEF_IP_MREQ 1
> +#endif
> +#if !defined(__UAPI_DEF_SOCKADDR_IN)
> #define __UAPI_DEF_SOCKADDR_IN 1
> +#endif
> +#if !defined(__UAPI_DEF_IN_CLASS)
> #define __UAPI_DEF_IN_CLASS 1
> +#endif
>
> /* Definitions for in6.h */
> +#if !defined(__UAPI_DEF_IN6_ADDR)
> #define __UAPI_DEF_IN6_ADDR 1
> +#endif
> +#if !defined(__UAPI_DEF_IN6_ADDR_ALT)
> #define __UAPI_DEF_IN6_ADDR_ALT 1
> +#endif
> +#if !defined(__UAPI_DEF_SOCKADDR_IN6)
> #define __UAPI_DEF_SOCKADDR_IN6 1
> +#endif
> +#if !defined(__UAPI_DEF_IPV6_MREQ)
> #define __UAPI_DEF_IPV6_MREQ 1
> +#endif
> +#if !defined(__UAPI_DEF_IPPROTO_V6)
> #define __UAPI_DEF_IPPROTO_V6 1
> +#endif
> +#if !defined(__UAPI_DEF_IPV6_OPTIONS)
> #define __UAPI_DEF_IPV6_OPTIONS 1
> +#endif
> +#if !defined(__UAPI_DEF_IN6_PKTINFO)
> #define __UAPI_DEF_IN6_PKTINFO 1
> +#endif
> +#if !defined(__UAPI_DEF_IP6_MTUINFO)
> #define __UAPI_DEF_IP6_MTUINFO 1
> +#endif
>
> /* Definitions for ipx.h */
> +#if !defined(__UAPI_DEF_SOCKADDR_IPX)
> #define __UAPI_DEF_SOCKADDR_IPX 1
> +#endif
> +#if !defined(__UAPI_DEF_IPX_ROUTE_DEFINITION)
> #define __UAPI_DEF_IPX_ROUTE_DEFINITION 1
> +#endif
> +#if !defined(__UAPI_DEF_IPX_INTERFACE_DEFINITION)
> #define __UAPI_DEF_IPX_INTERFACE_DEFINITION 1
> +#endif
> +#if !defined(__UAPI_DEF_IPX_CONFIG_DATA)
> #define __UAPI_DEF_IPX_CONFIG_DATA 1
> +#endif
> +#if !defined(__UAPI_DEF_IPX_ROUTE_DEF)
> #define __UAPI_DEF_IPX_ROUTE_DEF 1
> +#endif
>
> /* Definitions for xattr.h */
> +#if !defined(__UAPI_DEF_XATTR)
> #define __UAPI_DEF_XATTR 1
> +#endif
>
> #endif /* __GLIBC__ */
>
>