Linux include/uapi/linux/libc-compat.h and Musl include/netinet/in.h incompatibility for __UAPI_DEF_IN6_ADDR_ALT

[Chris Packham]

Hi,

I've come over from https://github.com/strace/strace/issues/177
there's a bit of context there.

Crosstool-ng has hit a problem when building a recent enough version
of strace in a configuration that uses musl libc.

The error is

[ALL  ]    In file included from
/home/x-tool/.build/arm-unknown-linux-musleabi/src/strace/bundled/linux/include/uapi/linux/in6.h:26,
[ALL  ]                     from
/home/x-tool/.build/arm-unknown-linux-musleabi/src/strace/bundled/linux/include/uapi/linux/if_bridge.h:19,
[ALL  ]                     from
/home/x-tool/.build/arm-unknown-linux-musleabi/src/strace/src/rtnl_mdb.c:16:
[ERROR]    /home/x-tool/.build/arm-unknown-linux-musleabi/src/strace/bundled/linux/include/uapi/linux/libc-compat.h:109:
error: "__UAPI_DEF_IN6_ADDR_ALT" redefined [-Werror]
[ALL  ]      109 | #define __UAPI_DEF_IN6_ADDR_ALT  1
[ALL  ]          |
[ALL  ]    In file included from
/home/x-tool/.build/arm-unknown-linux-musleabi/src/strace/src/rtnl_mdb.c:15:
[ALL  ]    /home/x-tool/x-tools/arm-unknown-linux-musleabi/arm-unknown-linux-musleabi/sysroot/usr/include/netinet/in.h:401:
note: this is the location of the previous definition
[ALL  ]      401 | #define __UAPI_DEF_IN6_ADDR_ALT 0
[ALL  ]          |
[ALL  ]    cc1: all warnings being treated as errors
[ERROR]    make[4]: *** [Makefile:6660: libstrace_a-rtnl_mdb.o] Error 1
[ALL  ]    make[4]: Leaving directory
'/home/x-tool/.build/arm-unknown-linux-musleabi/build/build-strace/src'
[ERROR]    make[3]: *** [Makefile:2404: all] Error 2
[ALL  ]    rm ioctlsort0.o ioctls_all0.h ioctlsort0
[ALL  ]    make[3]: Leaving directory
'/home/x-tool/.build/arm-unknown-linux-musleabi/build/build-strace/src'
[ERROR]    make[2]: *** [Makefile:601: all-recursive] Error 1
[ALL  ]    make[2]: Leaving directory
'/home/x-tool/.build/arm-unknown-linux-musleabi/build/build-strace'
[ERROR]    make[1]: *** [Makefile:506: all] Error 2
[ALL  ]    make[1]: Leaving directory
'/home/x-tool/.build/arm-unknown-linux-musleabi/build/build-strace'

It appears that the bundled uapi headers definition of
__UAPI_DEF_IN6_ADDR_ALT conflicts with the musl libc definition. It
looks like libc-compat.h tries to co-exists with GNU libc but this
isn't working for musl. I've identified an egregious hack that I think
should make things work (CFLAGS+=-D__USE_MISC) but I wanted to know if
there was a nicer way to make this work.

Regards,
Chris