[PATCH] Fix linux/stddef.h coordination with glibc (Bug 20215)

[Denys Vlasenko]

On 06/07/2016 11:55 AM, Carlos O'Donell wrote:
> Denys,
>
> In recent linux 4.6.0 headers we have this:
>
> git blame include/uapi/linux/stddef.h
> ~~~
> 607ca46e (David Howells  2012-10-13 10:46:48 +0100 1) #include <linux/compiler.h>
> 283d7573 (Denys Vlasenko 2016-03-30 00:14:57 +0200 2)
> 283d7573 (Denys Vlasenko 2016-03-30 00:14:57 +0200 3) #ifndef __always_inline
> 283d7573 (Denys Vlasenko 2016-03-30 00:14:57 +0200 4) #define __always_inline inline
> 283d7573 (Denys Vlasenko 2016-03-30 00:14:57 +0200 5) #endif
> ~~~
>
> The definition of __always_inline breaks certain header include
> ordering between glibc and linux headers.
>
> Mikko,
>
> I'm curious if your header include fuzzing script caught this failure?
>
> I am adding a source compile testing framework into glibc's test
> framework to add regression tests for these failures, rather than
> fuzz the whole set of headers. This way we can cover the problem
> from both sides glibc and linux:
> https://www.sourceware.org/ml/libc-alpha/2016-06/msg00162.html
>
> Test case:
> ~~~
> #include <linux/in6.h>
> #include <netinet/in.h>
>
> int
> main (void)
> {
>   return 0;
> }
> ~~~
> In file included from ../include/sys/cdefs.h:3:0,
>                  from ../include/features.h:368,
>                  from ../inet/netinet/in.h:21,
>                  from ../include/netinet/in.h:3,
>                  from ../sysdeps/unix/sysv/linux/tst-ipv6-compat2.c:2:
> ../misc/sys/cdefs.h:307:0: error: "__always_inline" redefined [-Werror]
>  # define __always_inline __inline __attribute__ ((__always_inline__))
>  ^
> In file included from /home/carlos/build/glibc-headers/include/linux/posix_types.h:4:0,
>                  from /home/carlos/build/glibc-headers/include/linux/types.h:8,
>                  from /home/carlos/build/glibc-headers/include/linux/in6.h:24,
>                  from ../sysdeps/unix/sysv/linux/tst-ipv6-compat2.c:1:
> /home/carlos/build/glibc-headers/include/linux/stddef.h:4:0: note: this is the location of the previous definition
>  #define __always_inline __inline__
>  ^
> cc1: all warnings being treated as errors
> ~~~
>
> The glibc definition, particularly the "__always_inline__" attribute needs
> to win out

Then an "#undef __always_inline" needs to be added before glibc #define.