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'Struct in6_addr does not have a name named' s6_addr32 with -ansi

I handle some compilation errors when creating OpenSSL using no-asm -ansi . I caught an error:

 $ ./config no-asm -ansi ... $ make ... gcc -DDSO_DLFCN -DHAVE_DLFCN_H -DOPENSSL_THREADS -DOPENSSL_NO_STATIC_ENGINE -DOPENSSL_PIC -DOPENSSLDIR="\"/usr/local/ssl\"" -DENGINESDIR="\"/usr/local/lib/engines\"" -Wall -O3 -pthread -m64 -DL_ENDIAN -ansi -fPIC -Iinclude -I. -Icrypto/include -MMD -MF crypto/bio/bss_dgram.d.tmp -MT crypto/bio/bss_dgram.o -c -o crypto/bio/bss_dgram.o crypto/bio/bss_dgram.c In file included from /usr/include/netdb.h:27:0, from ./e_os.h:443, from crypto/bio/bio_lcl.h:2, from crypto/bio/bss_dgram.c:62: crypto/bio/bss_dgram.c: In function 'dgram_get_mtu_overhead': crypto/bio/bss_dgram.c:433:20: error: 'const struct in6_addr' has no member named 's6_addr32' && IN6_IS_ADDR_V4MAPPED(&tmp_addr)) ^

I found the structure in /usr/include/linux/in6.h :

 #if __UAPI_DEF_IN6_ADDR struct in6_addr { union { __u8 u6_addr8[16]; #if __UAPI_DEF_IN6_ADDR_ALT __be16 u6_addr16[8]; __be32 u6_addr32[4]; #endif } in6_u; #define s6_addr in6_u.u6_addr8 #if __UAPI_DEF_IN6_ADDR_ALT #define s6_addr16 in6_u.u6_addr16 #define s6_addr32 in6_u.u6_addr32 #endif }; #endif /* __UAPI_DEF_IN6_ADDR */

I don’t remember having to define __UAPI_DEF_IN6_ADDR_ALT in the past. Finding it shows the following from the libc-compat.h , line 95 or so (if I parse it correctly):

 #define __UAPI_DEF_IN6_ADDR 1 /* We unconditionally define the in6_addr macros and glibc must coordinate. */ #define __UAPI_DEF_IN6_ADDR_ALT 1 #define __UAPI_DEF_SOCKADDR_IN6 1 #define __UAPI_DEF_IPV6_MREQ 1 #define __UAPI_DEF_IPPROTO_V6 1 #define __UAPI_DEF_IPV6_OPTIONS 1 #define __UAPI_DEF_IN6_PKTINFO 1 #define __UAPI_DEF_IP6_MTUINFO 1

How do I go about choosing alternative characters?

Ubuntu 14.04 system (x86_64):

 $ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 14.04.4 LTS Release: 14.04 Codename: trusty

GCC:

 $ gcc --version gcc (Ubuntu 4.8.4-2ubuntu1~14.04.1) 4.8.4 Copyright (C) 2013 Free Software Foundation, Inc.
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It turned out to be interesting ... In short, I needed to add both -ansi and -D_DEFAULT_SOURCE=1 . However, -D_DEFAULT_SOURCE=1 cancels what -ansi trying to do, so it should be contained.

Firstly, /usr/include/linux/in6.h was the wrong header. I found it through grep for struct in6_addr , and not the trace includes as needed.

Further ... -D_DEFAULT_SOURCE=1 indirectly came from /usr/include/netinet/in.h :

 #ifndef __USE_KERNEL_IPV6_DEFS /* IPv6 address */ struct in6_addr { union { uint8_t __u6_addr8[16]; #ifdef __USE_MISC uint16_t __u6_addr16[8]; uint32_t __u6_addr32[4]; #endif } __in6_u; #define s6_addr __in6_u.__u6_addr8 #ifdef __USE_MISC # define s6_addr16 __in6_u.__u6_addr16 # define s6_addr32 __in6_u.__u6_addr32 #endif }; #endif /* !__USE_KERNEL_IPV6_DEFS */

Manually enabling __USE_MISC failed. Tracking things for __USE_MISC in /usr/include/features.h :

 /* ... __USE_MISC Define things from 4.3BSD or System V Unix. ... */ #undef __USE_MISC ... #if defined _DEFAULT_SOURCE # define __USE_MISC 1 #endif

And finally, from the comment in /usr/include/features.h :

 _DEFAULT_SOURCE The default set of features (taking precedence over __STRICT_ANSI__).

Although _DEFAULT_SOURCE=1 deviates from -ansi , exposure may be limited to a single source file, which is affected by IN6_IS_ADDR_V4MAPPED . That is, for the C source file crypto/bio/bss_dgram.c :

 /* OpenSSL copyright ... */ #ifndef _DEFAULT_SOURCE # define _DEFAULT_SOURCE 1 #endif #include <stdio.h> #include <errno.h> #include <netinet/in.h> ...

Twisting __USE_KERNEL_IPV6_DEFS made things even worse. I believe that he activated /usr/include/linux/in6.h , which had similar (but completely different) member names than <netinet/in.h> .

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