Bug 138016 – [3.4] gcc -Wunreachable-code gives false positive

• Product: Gentoo Linux
• Status: VERIFIED WORKSFORME

[Description Christopher Head 2006-06-26 00:14:52 UTC]

# emerge --info
Portage 2.1-r1 (default-linux/x86/2006.0, gcc-3.4.6, glibc-2.3.6-r4, 2.6.16-gentoo-r9 i686)
=================================================================
System uname: 2.6.16-gentoo-r9 i686 Celeron (Mendocino)
Gentoo Base System version 1.6.15
dev-lang/python:     2.4.2
dev-python/pycrypto: 2.0.1-r5
dev-util/ccache:     [Not Present]
dev-util/confcache:  [Not Present]
sys-apps/sandbox:    1.2.17
sys-devel/autoconf:  2.13, 2.59-r7
sys-devel/automake:  1.4_p6, 1.5, 1.6.3, 1.7.9-r1, 1.8.5-r3, 1.9.6-r1
sys-devel/binutils:  2.16.1-r2
sys-devel/gcc-config: 1.3.13-r2
sys-devel/libtool:   1.5.22
virtual/os-headers:  2.6.11-r2
ACCEPT_KEYWORDS="x86"
AUTOCLEAN="yes"
CBUILD="i686-pc-linux-gnu"
CFLAGS="-Os -march=i686 -pipe -momit-leaf-frame-pointer -fomit-frame-pointer -fweb -frename-registers"
CHOST="i686-pc-linux-gnu"
CONFIG_PROTECT="/etc /usr/lib/X11/xkb"
CONFIG_PROTECT_MASK="/etc/env.d /etc/gconf /etc/revdep-rebuild /etc/terminfo"
CXXFLAGS="-Os -march=i686 -pipe -momit-leaf-frame-pointer -fomit-frame-pointer -fweb -frename-registers"
DISTDIR="/usr/portage/distfiles"
FEATURES="autoconfig distlocks metadata-transfer sandbox sfperms strict"
GENTOO_MIRRORS="http://adelie.polymtl.ca/ ftp://cs.ubishops.ca/pub/gentoo ftp://gentoo.arcticnetwork.ca/pub/gentoo/ http://gentoo.arcticnetwork.ca/ http://gentoo.mirrored.ca/ ftp://gentoo.mirrored.ca/ "
LANG="en_CA.utf8"
LC_ALL="en_CA.utf8"
LINGUAS="en"
MAKEOPTS="-j1"
PKGDIR="/usr/portage/packages"
PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --compress --force --whole-file --delete --delete-after --stats --timeout=180 --exclude='/distfiles' --exclude='/local' --exclude='/packages'"
PORTAGE_TMPDIR="/var/tmp"
PORTDIR="/usr/portage"
PORTDIR_OVERLAY="/usr/local/portage"
SYNC="rsync://rsync.namerica.gentoo.org/gentoo-portage"
USE="x86 3dfx X acpi alsa apache2 avi bitmap-fonts bzip2 cli crypt dga dri dvd fam gdbm gif gimp glibc-omitfp gmp gstreamer gtk gtk2 hpn idea isdnlog java javascript jpeg libg++ libwww mmx mpeg ncurses nls nptl nptlonly nsplugin opengl pam pcre pdflib png pppd qt quicktime readline reflection samba scanner sdl session spell spl ssl symlink truetype truetype-fonts type1-fonts ucs2 udev unicode usb userlocales voodoo3 xml xml2 xmms xorg xscreensaver xv zlib elibc_glibc kernel_linux linguas_en userland_GNU"
Unset:  CTARGET, EMERGE_DEFAULT_OPTS, INSTALL_MASK, LDFLAGS, PORTAGE_RSYNC_EXTRA_OPTS

# gcc --version
gcc (GCC) 3.4.6 (Gentoo 3.4.6-r1, ssp-3.4.5-1.0, pie-8.7.9)
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

# cat helper2.c
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/ppdev.h>
#include <linux/parport.h>

int open_device(const char *dev) {
        int handle;
        int arg;

        handle = open(dev, O_RDWR);
        if (handle < 0) {
                return -1;
        }
        if (ioctl(handle, PPEXCL) < 0) {
                close(handle);
                return -1;
        }
        if (ioctl(handle, PPCLAIM) < 0) {
                close(handle);
                return -1;
        }
        arg = IEEE1284_MODE_COMPAT;
        if (ioctl(handle, PPSETMODE, &arg) < 0) {
                ioctl(handle, PPRELEASE);
                close(handle); /* LINE 28 */
                return -1;
        }
        arg = 0;
        if (ioctl(handle, PPSETFLAGS, &arg) < 0) {
                ioctl(handle, PPRELEASE);
                close(handle); /* LINE 34 */
                return -1;
        }
        arg = 0;
        if (ioctl(handle, PPDATADIR, &arg) < 0) {
                ioctl(handle, PPRELEASE);
                close(handle);
                return -1;
        }
        return handle;
}

# gcc -olibLPTLinux-Helper.so -pipe -ansi -pedantic -Wall -Wextra -Wshadow -Wpointer-arith -Wbad-function-cast -Wcast-qual -Wcast-align -Wwrite-strings -Wconversion -Wstrict-prototypes -Wold-style-definition -Wpacked -Wnested-externs -Wunreachable-code -Wstack-protector -g0 -Os -s -fpic -fstack-protector-all -fno-leading-underscore -shared helper2.c
helper2.c: In function `open_device':
helper2.c:34: warning: will never be executed
helper2.c:28: warning: will never be executed

The relevant lines have been commented in the source listing above. This output is clearly wrong; the ioctl() function will return and close() will be invoked. I have absolutely no idea why GCC would say this, it makes no sense to me.

[Comment 1 SpanKY 2006-06-26 15:54:55 UTC]

this has been fixed in gcc-4.x so really this is going to stay broken forever