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Message-ID: <a360ec42-33ca-5e89-3d70-3b1c9a011c7f@redhat.com>
Date: Wed, 8 Mar 2017 10:53:00 -0500
From: Carlos O'Donell <carlos@...hat.com>
To: linux-kernel@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
linux-api@...r.kernel.org, musl@...ts.openwall.com,
Rich Felker <dalias@...ifal.cx>
Subject: Re: [PATCH resent] uapi libc compat: allow non-glibc to opt out of
uapi definitions
On 11/11/2016 07:08 AM, Felix Janda wrote:
> Currently, libc-compat.h detects inclusion of specific glibc headers,
> and defines corresponding _UAPI_DEF_* macros, which in turn are used in
> uapi headers to prevent definition of conflicting structures/constants.
> There is no such detection for other c libraries, for them the
> _UAPI_DEF_* macros are always defined as 1, and so none of the possibly
> conflicting definitions are suppressed.
>
> This patch enables non-glibc c libraries to request the suppression of
> any specific interface by defining the corresponding _UAPI_DEF_* macro
> as 0.
>
> This patch together with the recent musl libc commit
>
> http://git.musl-libc.org/cgit/musl/commit/?id=04983f2272382af92eb8f8838964ff944fbb8258
Would it be possible to amend the musl patch to define the macros to 1.
A defined or undefined macro is typo prone.
Please see this wiki for examples of the problems it causes:
https://sourceware.org/glibc/wiki/Wundef
Having the UAPI macros always defined and be 0 or 1 allows you to create
tooling to check for problems, while an undefined macro is just that,
either a mistake or the intended value.
> fixes the following compiler errors when <linux/in6.h> is included
> after musl <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'
Do you have plans for fixing the error when the inclusion order is the other way?
It will require kernel header changes to have each individual kernel header define
the requisite __UAPI_* values to 1 e.g. moving libc-compat.h into the header.
Do you plan to do that in a next step?
> Signed-off-by: Felix Janda <felix.janda@...teo.de>
> ---
> The previous mail misspelled the kernel mailing list. I am sorry for
> this resulting spam.
>
> There has already been one reply, which is available at
>
> http://www.openwall.com/lists/musl/2016/11/11/2
> ---
> include/uapi/linux/libc-compat.h | 52 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 52 insertions(+)
>
> 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__) */
Would you please update the lead comment in libc-compat.h explaining this usage
model so glibc and other libc's can follow best practice. Any new usage model
should express how to fix header inclusion ordering in both directions.
> /* Definitions for if.h */
> +#if !defined(__UAPI_DEF_IF_IFCONF)
Typo prone. Please use #if __UAPI_DEF_IF_IFCONF for all of this.
> #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)
> #define __UAPI_DEF_IF_IFNAMSIZ 1
> +#endif
> +#if !defined(__UAPI_DEF_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__ */
>
>
--
Cheers,
Carlos.
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