Re: superfluous space char in marco

[Rich Felker <dalias@libc.org>]

On Sun, Apr 16, 2017 at 03:58:11PM +0800, Syrone Wong wrote:
> For include/net/if.h, we define it as
> 
> #define IFF_VOLATILE (IFF_LOOPBACK|IFF_POINTOPOINT|IFF_BROADCAST| \
>         IFF_ECHO|IFF_MASTER|IFF_SLAVE|IFF_RUNNING|IFF_LOWER_UP|IFF_DORMANT)
> 
> while iproute2 4.10.0 define it as
> 
> #define IFF_VOLATILE (IFF_LOOPBACK|IFF_POINTOPOINT|IFF_BROADCAST|IFF_ECHO|\
> IFF_MASTER|IFF_SLAVE|IFF_RUNNING|IFF_LOWER_UP|IFF_DORMANT)
> 
> in include/linux/if.h. The only difference is the space char after
> IFF_BROADCAST.

Do the other iproute2 include/linux/* headers actually work now? My
experience building it in the past has been that you have to rm -rf
that directory to get it to build at all since it contained outdated
and clashing versions of those headers. Maybe something has changed in
recent versions.

> This causes the redefinition of IFF_VOLATILE.
> 
> Warning when compiling iproute2 4.10.0:
> 
> In file included from ../include/linux/if_tunnel.h:5:0,
>                  from iptunnel.c:24:
> .../include/linux/if.h:130:0: warning: "IFF_VOLATILE" redefined
>  #define IFF_VOLATILE (IFF_LOOPBACK|IFF_POINTOPOINT|IFF_BROADCAST|IFF_ECHO|\
> 
> In file included from iptunnel.c:21:0:
> /home/wong/github/lede-1/staging_dir/toolchain-arm_cortex-a9+vfpv3_gcc-6.3.0_musl_eabi/include/net/if.h:48:0:
> note: this is the location of the previous definition
>  #define IFF_VOLATILE (IFF_LOOPBACK|IFF_POINTOPOINT|IFF_BROADCAST| \

This is odd and looks like a gcc bug. Preprocessor macros definitions
are sequences of PP tokens, not literal code strings, meaning that
whitespace is irrelevant as long as the resulting sequence of PP
tokens remains the same; it's a matching definition not a
redefinition.

Anyone else have thoughts on what's going on?

Rich