Hello, probably I'm missing something, but it happens that the trivial snippet here below segfaults on my amd64 dual-header box. The issue goes away simply uncommenting the below #include. #include <stdio.h> #include <netinet/in.h> /* uncomment me to solve the problem! */ /* #include <arpa/inet.h> */ int main(void) { struct in_addr io = { 0x100007f }; printf("%s\n", inet_ntoa(io)); // <-- segfaults return 0; } Reproducible: Always Steps to Reproduce: 1. Save the snippet in issue.c 2. gcc issue.c -o issue 3. ./issue Actual Results: <0> $ ./issue Segmentation fault Syslog reports: Feb 12 00:12:43 s_kernel@longinus issue[10702]: segfault at 4e4976c0 ip 00007f104dfcaaf0 sp 00007fff564adc38 error 4 in libc-2.6.1.so[7f104df57000+136000] Expected Results: <0> $ ./issue 127.0.0.1 <0> $ emerge --info Portage 2.1.6.4 (default/linux/amd64/2008.0/desktop, gcc-4.1.2, glibc-2.6.1-r0, 2.6.28.1 x86_64) ================================================================= System uname: Linux-2.6.28.1-x86_64-Intel-R-_Core-TM-2_CPU_T7200_@_2.00GHz-with-glibc2.2.5 Timestamp of tree: Mon, 09 Feb 2009 11:45:01 +0000 ccache version 2.4 [enabled] app-shells/bash: 3.2_p39 dev-java/java-config: 1.3.7-r1, 2.1.6-r1 dev-lang/python: 2.5.2-r7 dev-util/ccache: 2.4-r7 sys-apps/baselayout: 1.12.11.1 sys-apps/sandbox: 1.2.18.1-r2 sys-devel/autoconf: 2.13, 2.63 sys-devel/automake: 1.7.9-r1, 1.8.5-r3, 1.9.6-r2, 1.10.2 sys-devel/binutils: 2.18-r3 sys-devel/gcc-config: 1.4.0-r4 sys-devel/libtool: 1.5.26 virtual/os-headers: 2.6.27-r2 ACCEPT_KEYWORDS="amd64" CBUILD="x86_64-pc-linux-gnu" CFLAGS="-march=nocona -O3 -pipe" CHOST="x86_64-pc-linux-gnu" CONFIG_PROTECT="/etc /var/qmail/alias /var/qmail/control" CONFIG_PROTECT_MASK="/etc/ca-certificates.conf /etc/env.d /etc/env.d/java/ /etc/fonts/fonts.conf /etc/gconf /etc/revdep-rebuild /etc/terminfo /etc/texmf/web2c /etc/udev/rules.d" CXXFLAGS="-march=nocona -O3 -pipe" DISTDIR="/usr/portage/distfiles" FEATURES="ccache distlocks fixpackages metadata-transfer notitles parallel-fetch protect-owned sandbox sfperms strict unmerge-orphans userfetch userpriv usersandbox" GENTOO_MIRRORS="http://mirror.muntinternet.net/pub/gentoo/ http://mirrors.sec.informatik.tu-darmstadt.de/gentoo/ http://mirror.switch.ch/ftp/mirror/gentoo/ http://mirror.bytemark.co.uk/gentoo/ http://ftp.uni-erlangen.de/pub/mirrors/gentoo" LDFLAGS="-Wl,-O1" LINGUAS="en" MAKEOPTS="-j3" PKGDIR="/usr/portage/packages" PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --compress --force --whole-file --delete --stats --timeout=180 --exclude=/distfiles --exclude=/local --exclude=/packages" PORTAGE_TMPDIR="/var/tmp" PORTDIR="/usr/portage" PORTDIR_OVERLAY="/usr/portage/local/layman/enlightenment /usr/local/portage" SYNC="rsync://rsync.europe.gentoo.org/gentoo-portage" USE="X aac acpi alsa amd64 aspell bash-completion berkdb bluetooth branding bzip2 cairo cdr cjk cracklib crypt cups dbus dri dts dvd dvdr dvdread emacs encode esd fam firefox gd gdbm gencertdaily gif gimp gpm hal iconv imagemagick imap imlib ipv6 jabber java jpeg jpeg2k latex libnotify lm_sensors mad midi mmx mmxext mp3 mpeg mplayer multilib ncurses nls nonfsv4 nptl nptlonly nsplugin nvidia ogg opengl pam pcre pdf perl plotutils png portage ppds python qmail readline remote rtc sdl sensord session slp spell srt sse sse2 ssl ssse3 startup-notification subversion sysfs tcl tcpd tetex threads tiff tk truetype unicode usb vorbis wifi xanim xml xorg xpm xulrunner xv xvid xvmc zlib" ALSA_CARDS="ali5451 als4000 atiixp atiixp-modem bt87x ca0106 cmipci emu10k1x ens1370 ens1371 es1938 es1968 fm801 hda-intel intel8x0 intel8x0m maestro3 trident usb-audio via82xx via82xx-modem ymfpci" ALSA_PCM_PLUGINS="adpcm alaw asym copy dmix dshare dsnoop empty extplug file hooks iec958 ioplug ladspa lfloat linear meter mmap_emul mulaw multi null plug rate route share shm softvol" APACHE2_MODULES="actions alias auth_basic authn_alias authn_anon authn_dbm authn_default authn_file authz_dbm authz_default authz_groupfile authz_host authz_owner authz_user autoindex cache dav dav_fs dav_lock deflate dir disk_cache env expires ext_filter file_cache filter headers include info log_config logio mem_cache mime mime_magic negotiation rewrite setenvif speling status unique_id userdir usertrack vhost_alias" ELIBC="glibc" INPUT_DEVICES="evdev keyboard mouse synaptics" KERNEL="linux" LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses text" LINGUAS="en" USERLAND="GNU" VIDEO_CARDS="nvidia intel" Unset: CPPFLAGS, CTARGET, EMERGE_DEFAULT_OPTS, FFLAGS, INSTALL_MASK, LANG, LC_ALL, PORTAGE_COMPRESS, PORTAGE_COMPRESS_FLAGS, PORTAGE_RSYNC_EXTRA_OPTS
I think to have discovered what happens. When the #include is commented out, the compiler uses the 32bit funcall in place of the needed 64bit one. Here below is the corresponding assembly snippet for both versions: /* #include <arpa/inet.h> */ movl $16777343, -16(%rbp) movl -16(%rbp), %edi movl $0, %eax call inet_ntoa cltq movq %rax, -8(%rbp) movq -8(%rbp), %rdi call puts movl $0, %eax #include <arpa/inet.h> movl $16777343, -16(%rbp) movl -16(%rbp), %edi call inet_ntoa movq %rax, -8(%rbp) movq -8(%rbp), %rdi call puts movl $0, %eax As you can see, the #include-less version uses the cltq (aka cdqe) to convert the doubleword in eax to a quadword in rax with the same numerical value. Probably this value is not as good as it should (see below) 4 /* uncomment me to solve the problem! */ 5 /* #include <arpa/inet.h> */ 6 7 int main(void) 8 { 9 struct in_addr io = { 0x100007f }; 10 char *x = inet_ntoa(io); 11 12 printf("%s\n", x); (gdb) s 9 struct in_addr io = { 0x100007f }; (gdb) s 10 char *x = inet_ntoa(io); (gdb) s 12 printf("%s\n", x); (gdb) p x $1 = 0x478e76c0 <Address 0x478e76c0 out of bounds>
OK, I solved. Without the #include, gcc assumes that inet_ntoa() returns an integer (4 bytes). Differently on x86, this is unable to store memory addresses (char * is 8 bytes long in amd64 architecture), so the cltq instruction does nothing but extending an already truncated address and the printf segfaults. Sorry for any inconvenience
you probably ignored the warnings. implicit decls -> int return type.
Yeah, usually I don't! Since the snippet came by a well-known network book, this time I "forgot" the -Wall..
