new features: new address types SCTP-CONNECT and SCTP-LISTEN implement SCTP stream mode for IPv4 and IPv6; new address options sctp-maxseg and sctp-nodelay added generic socket addresses: SOCKET-CONNECT, SOCKET-LISTEN, SOCKET-SENDTO, SOCKET-RECVFROM, SOCKET-RECV, SOCKET-DATAGRAM allow protocol independent socket handling; all parameters are explicitely specified as numbers or hex data added address options ioctl-void, ioctl-int, ioctl-intp, ioctl-string, ioctl-bin for generic ioctl() calls. added address options setsockopt-int, setsockopt-bin, and setsockopt-string so-type now only affect the socket() and socketpair() calls, not the name resolution. so-type and so-prototype can be applied to all socket based addresses. new address option "escape" allows to break a socat instance even when raw terminal mode prevents ^C etc. socat sets environment variables SOCAT_VERSION, SOCAT_PID, SOCAT_PPID for use in executed scripts socat sets environment variables SOCAT_SOCKADDR, SOCAT_SOCKPORT, SOCAT_PEERADDR, SOCAT_PEERPORT in LISTEN type addresses (feature suggested by Ed Sawicki) socat receives all ancillary messages with each received packet on datagram related addresses. The messages are logged in raw form with debug level, and broken down with info level. note: each type of ancillary message must be enabled by appropriate address options. socat provides the contents of ancillary messages received on RECVFROM addresses in appropriate environment variables: SOCAT_IP_PKTINFO_DSTADDR, SOCAT_IP_PKTINFO_IF, SOCAT_IP_PKTINFO_LOCADDR (not on BSD); SOCAT_IP_RECVDSTADDR, SOCAT_IP_RECVIF (BSD); SOCAT_SCM_TIMESTAMP, SOCAT_IP_OPTIONS, SOCAT_IP_TOS, SOCAT_IP_TTL, SOCAT_IPV6_HOPLIMIT, SOCAT_IPV6_TCLASS, SOCAT_IPV6_PKTINFO_DSTADDR the following address options were added to enable ancillary messages: so-timestamp, ip-pktinfo, ip-recvdstaddr, ip-recverr, ip-recvif, ip-recvopts, ip-recvtos, ip-recvttl, ipv6-recvdstopts, ipv6-recverr, ipv6-recvhoplimit, ipv6-recvhopopts, ipv6-recvpathmtu, ipv6-recvpktinfo, ipv6-recvrthdr, ipv6-recvtclass new address options ipv6-tclass and ipv6-unicast-hops set the related socket options. corrections: some raw IP and UNIX datagram modes failed on BSD systems when UDP-LISTEN continued to listen after packet dropped by, e.g., range option, the old listen socket would not be closed but a new one created. open sockets could accumulate. there was a bug in ip*-recv with bind option: it did not bind, and with the first received packet an error occurred: socket_init(): unknown address family 0 test: RAWIP4RECVBIND RECVFROM addresses with FORK option hung after processing the first packet. test: UDP4RECVFROM_FORK corrected a few mistakes that caused compiler warnings on 64bit hosts EXEC and SYSTEM with stderr injected socat messages into the data stream. test: EXECSTDERRLOG when the EXEC address got a string with consecutive spaces it created additional empty arguments (thanks to Olivier Hervieu for reporting this bug). test: EXECSPACES in ignoreeof polling mode socat also blocked data transfer in the other direction during the 1s wait intervalls (thanks to Jorgen Cederlof for reporting this bug) corrected alphabetical order of options (proxy-auth) some minor corrections improved test.sh script: more stable timing, corrections for BSD replaced the select() calls by poll() to cleanly fix the problems with many file descriptors already open porting: socat should now build under MacOS X 10.4 (thanks to Camillo Lugaresi for providing the patch) further changes: filan -s prefixes output with FD number if more than one FD Makefile now supports datarootdir (thanks to Camillo Lugaresi for providing the patch) cleanup in xio-unix.c ####################### V 1.6.0.1: new features: new make target "gitclean" docu source doc/socat.yo released corrections: exec:...,pty did not kill child process under some circumstances; fixed by correcting typo in xio-progcall.c (thanks to Ralph Forsythe for reporting this problem) service name resolution failed due to byte order mistake (thanks to James Sainsbury for reporting this problem) socat would hang when invoked with many file descriptors already opened fix: replaced FOPEN_MAX with FD_SETSIZE thanks to Daniel Lucq for reporting this problem. fixed bugs where sub processes would become zombies because the master process did not catch SIGCHLD. this affected addresses UDP-LISTEN, UDP-CONNECT, TCP-CONNECT, OPENSSL, PROXY, UNIX-CONNECT, UNIX-CLIENT, ABSTRACT-CONNECT, ABSTRACT-CLIENT, SOCKSA, SOCKS4A (thanks to Fernanda G Weiden for reporting this problem) fixed a bug where sub processes would become zombies because the master process caught SIGCHLD but did not wait(). this affected addresses UDP-RECVFROM, IP-RECVFROM, UNIX-RECVFROM, ABSTRACT-RECVFROM (thanks to Evan Borgstrom for reporting this problem) corrected option handling with STDIO; usecase: cool-write configure --disable-pty also disabled option waitlock fixed small bugs on systems with struct ip_mreq without struct ip_mreqn (thanks to Roland Illig for sending a patch) corrected name of option intervall to interval (old form still valid for us German speaking guys) corrected some print statements and variable names make uninstall did not uninstall procan fixed lots of weaknesses in test.sh corrected some bugs and typos in doc/socat.yo, EXAMPLES, C comments further changes: procan -c prints C defines important for socat added test OPENSSLEOF for OpenSSL half close ####################### V 1.6.0.0: new features: new addresses IP-DATAGRAM and UDP-DATAGRAM allow versatile broadcast and multicast modes new option ip-add-membership for control of multicast group membership new address TUN for generation of Linux TUN/TAP pseudo network interfaces (suggested by Mat Caughron); associated options tun-device, tun-name, tun-type; iff-up, iff-promisc, iff-noarp, iff-no-pi etc. new addresses ABSTRACT-CONNECT, ABSTRACT-LISTEN, ABSTRACT-SENDTO, ABSTRACT-RECV, and ABSTRACT-RECVFROM for abstract UNIX domain addresses on Linux (requested by Zeeshan Ali); option unix-tightsocklen controls socklen parameter on system calls. option end-close for control of connection closing allows FD sharing by sub processes range option supports form address:mask with IPv4 changed behaviour of SSL-LISTEN to require and verify client certificate per default options f-setlkw-rd, f-setlkw-wr, f-setlk-rd, f-setlk-wr allow finer grained locking on regular files uninstall target in Makefile (lack reported by Zeeshan Ali) corrections: fixed bug where only first tcpwrap option was applied; fixed bug where tcpwrap IPv6 check always failed (thanks to Rudolf Cejka for reporting and fixing this bug) filan (and socat -D) could hang when a socket was involved corrected PTYs on HP-UX (and maybe others) using STREAMS (inspired by Roberto Mackun) correct bind with udp6-listen (thanks to Jan Horak for reporting this bug) corrected filan.c peekbuff[0] which did not compile with Sun Studio Pro (thanks to Leo Zhadanovsky for reporting this problem) corrected problem with read data buffered in OpenSSL layer (thanks to Jon Nelson for reporting this bug) corrected problem with option readbytes when input stream stayed idle after so many bytes fixed a bug where a datagram receiver with option fork could fork two sub processes per packet further changes: moved documentation to new doc/ subdir new documents (kind of mini tutorials) are provided in doc/ ####################### V 1.5.0.0: new features: new datagram modes for udp, rawip, unix domain sockets socat option -T specifies inactivity timeout rewrote lexical analysis to allow nested socat calls addresses tcp, udp, tcp-l, udp-l, and rawip now support IPv4 and IPv6 socat options -4, -6 and environment variables SOCAT_DEFAULT_LISTEN_IP, SOCAT_PREFERRED_RESOLVE_IP for control of protocol selection addresses ssl, ssl-l, socks, proxy now support IPv4 and IPv6 option protocol-family (pf), esp. for openssl-listen range option supports IPv6 - syntax: range=[::1/128] option ipv6-v6only (ipv6only) new tcp-wrappers options allow-table, deny-table, tcpwrap-etc FIPS version of OpenSSL can be integrated - initial patch provided by David Acker. See README.FIPS support for resolver options res-debug, aaonly, usevc, primary, igntc, recurse, defnames, stayopen, dnsrch options for file attributes on advanced filesystems (ext2, ext3, reiser): secrm, unrm, compr, ext2-sync, immutable, ext2-append, nodump, ext2-noatime, journal-data etc. option cool-write controls severeness of write failure (EPIPE, ECONNRESET) option o-noatime socat option -lh for hostname in log output traffic dumping provides packet headers configure.in became part of distribution socats unpack directory now has full version, e.g. socat-1.5.0.0/ corrected docu of option verify corrections: fixed tcpwrappers integration - initial fix provided by Rudolf Cejka exec with pipes,stderr produced error setuid-early was ignored with many address types some minor corrections ####################### V 1.4.3.1: corrections: PROBLEM: UNIX socket listen accepted only one (or a few) connections. FIX: do not remove listening UNIX socket in child process PROBLEM: SIGSEGV when TCP part of SSL connect failed FIX: check ssl pointer before calling SSL_shutdown In debug mode, show connect client port even when connect fails ####################### V 1.4.3.0: new features: socat options -L, -W for application level locking options "lockfile", "waitlock" for address level locking (Stefan Luethje) option "readbytes" limits read length (Adam Osuchowski) option "retry" for unix-connect, unix-listen, tcp6-listen (Dale Dude) pty symlink, unix listen socket, and named pipe are per default removed after use; option unlink-close overrides this new behaviour and also controls removal of other socat generated files (Stefan Luethje) corrections: option "retry" did not work with tcp-listen EPIPE condition could result in a 100% CPU loop further changes: support systems without SHUT_RD etc. handle more size_t types try to find makedepend options with gcc 3 (richard/OpenMacNews) ####################### V 1.4.2.0: new features: option "connect-timeout" limits wait time for connect operations (requested by Giulio Orsero) option "dhparam" for explicit Diffie-Hellman parameter file corrections: support for OpenSSL DSA certificates (Miika Komu) create install directories before copying files (Miika Komu) when exiting on signal, return status 128+signum instead of 1 on EPIPE and ECONNRESET, only issue a warning (Santiago Garcia Mantinan) -lu could cause a core dump on long messages further changes: modifications to simplify using socats features in applications ####################### V 1.4.1.0: new features: option "wait-slave" blocks open of pty master side until a client connects, "pty-intervall" controls polling option -h as synonym to -? for help (contributed by Christian Lademann) filan prints formatted time stamps and rdev (disable with -r) redirect filan's output, so stdout is not affected (contributed by Luigi Iotti) filan option -L to follow symbolic links filan shows termios control characters corrections: proxy address no longer performs unsolicited retries filan -f no longer needs read permission to analyze a file (but still needs access permission to directory, of course) porting: Option dsusp FreeBSD options noopt, nopush, md5sig OpenBSD options sack-disable, signature-enable HP-UX, Solaris options abort-threshold, conn-abort-threshold HP-UX options b900, b3600, b7200 Tru64/OSF1 options keepinit, paws, sackena, tsoptena further corrections: address pty now uses ptmx as default if openpty is also available ####################### V 1.4.0.3: corrections: fix to a syslog() based format string vulnerability that can lead to remote code execution. See advisory socat-adv-1.txt ####################### V 1.4.0.2: corrections: exec'd write-only addresses get a chance to flush before being killed error handler: print notice on error-exit filan printed wrong file type information ####################### V 1.4.0.1: corrections: socks4a constructed invalid header. Problem found, reported, and fixed by Thomas Themel, by Peter Palfrader, and by rik with nofork, don't forget to apply some process related options (chroot, setsid, setpgid, ...) ####################### V 1.4.0.0: new features: simple openssl server (ssl-l), experimental openssl trust new options "cafile", "capath", "key", "cert", "egd", and "pseudo" for openssl new options "retry", "forever", and "intervall" option "fork" for address TCP improves `gender changer´ options "sigint", "sigquit", and "sighup" control passing of signals to sub process (thanks to David Shea who contributed to this issue) readline takes respect to the prompt issued by the peer address options "prompt" and "noprompt" allow to override readline's new default behaviour readline supports invisible password with option "noecho" socat option -lp allows to set hostname in log output socat option -lu turns on microsecond resolution in log output corrections: before reading available data, check if writing on other channel is possible tcp6, udp6: support hostname specification (not only IP address), and map IP4 names to IP6 addresses openssl client checks server certificate per default support unidirectional communication with exec/system subprocess try to restore original terminal settings when terminating test.sh uses tmp dir /tmp/$USER/$$ instead of /tmp/$$ socks4 failed on platforms where long does not have 32 bits (thanks to Peter Palfrader and Thomas Seyrat) hstrerror substitute wrote wrong messages (HP-UX, Solaris) proxy error message was truncated when answer contained multiple spaces porting: compiles with AIX xlc, HP-UX cc, Tru64 cc (but might not link) ####################### V 1.3.2.2: corrections: PROXY CONNECT failed when the status reply from the proxy server contained more than one consecutive spaces. Problem reported by Alexandre Bezroutchko do not SIGSEGV when proxy address fails to resolve server name udp-listen failed on systems where AF_INET != SOCK_DGRAM (e.g. SunOS). Problem reported by Christoph Schittel test.sh only tests available features added missing IP and TCP options in filan analyzer do not apply stdio address options to both directions when in unidirectional mode on systems lacking /dev/*random and egd, provide (weak) entropy from libc random() porting: changes for HP-UX (VREPRINT, h_NETDB_INTERNAL) compiles on True64, FreeBSD (again), NetBSD, OpenBSD support for long long as st_ino type (Cygwin 1.5) compile on systems where pty can not be featured ####################### V 1.3.2.1: corrections: "final" solution for the ENOCHLD problem corrected "make strip" default gcc debug/opt is "-O" again check for /proc at runtime, even if configure found it src.rpm accidently supported SuSE instead of RedHat ####################### V 1.3.2.0: new features: option "nofork" connects an exec'd script or program directly to the file descriptors of the other address, circumventing the socat transfer engine support for files >2GB, using ftruncate64(), lseek64(), stat64() filan has new "simple" output style (filan -s) porting: options "binary" and "text" for controlling line termination on Cygwin file system access (hint from Yang Wu-Zhou) fix by Yang Wu-Zhou for the Cygwin "No Children" problem improved support for OSR: _SVID3; no IS_SOCK, no F_GETOWN (thanks to John DuBois) minor corrections to avoid warnings with gcc 3 further corrections and minor improvements: configure script is generated with autoconf 2.57 (no longer 2.52) configure passes CFLAGS to Makefile option -??? for complete list of address options and their short forms program name in syslog messages is derived from argv[0] SIGHUP now prints notice instead of error EIO during read of pty now gives Notice instead of Error, and triggers EOF use of hstrerror() for printing resolver error messages setgrent() got required endgrent() ####################### V 1.3.1.0: new features: integration of Wietse Venema's tcpwrapper library (libwrap) with "proxy" address, option "resolve" controls if hostname or IP address is sent in request option "lowport" establishes limited authorization for TCP and UDP connections improvement of .spec file for RPM creation (thanks to Gerd v. Egidy) An accompanying change in the numbering scheme results in an incompatibility with earlier socat RPMs! solved problems and bugs: PROBLEM: socat daemon terminated when the address of a connecting client did not match range option value instead of continue listening SOLVED: in this case, print warning instead of error to keep daemon active PROBLEM: tcp-listen with fork sometimes left excessive number of zombie processes SOLVED: dont assume that each exiting child process generates SIGCHLD when converting CRNL to CR, socat converted to NL further corrections: configure script now disables features that depend on missing files making it more robust in "unsupported" environments server.pem permissions corrected to 600 "make install" now does not strip; use "make strip; make install" if you like strip (suggested by Peter Bray) ####################### V 1.3.0.1: solved problems and bugs: PROBLEM: OPENSSL did not apply tcp, ip, and socket options SOLVED: OPENSSL now correctly handles the options list PROBLEM: CRNL to NL and CRNL to CR conversions failed when CRNL crossed block boundary SOLVED: these conversions now simply strip all CR's or NL's from input stream porting: SunOS ptys now work on x86, too (thanks to Peter Bray) configure looks for freeware libs in /pkgs/lib/ (thanks to Peter Bray) further corrections: added WITH_PROXY value to -V output added compile dependencies of WITH_PTY and WITH_PROXY -?? did not print option group of proxy options corrected syntax for bind option in docu corrected an issue with stdio in unidirectional mode options socksport and proxyport support service names ftp.sh script supports proxy address man page no longer installed with execute permissions (thanks to Peter Bray) fixed a malloc call bug that could cause SIGSEGV or false "out of memory" errors on EXEC and SYSTEM, depending on program name length and libc. ####################### V 1.3.0.0: new features: proxy connect with optional proxy authentication combined hex and text dump mode, credits to Gregory Margo address pty applies options user, group, and perm to device solved problems and bugs: PROBLEM: option reuseport was not applied (BSD, AIX) SOLVED: option reuseport now in phase PASTSOCKET instead of PREBIND, credits to Jean-Baptiste Marchand PROBLEM: ignoreeof with stdio was ignored SOLVED: ignoreeof now works correctly with address stdio PROBLEM: ftp.sh did not use user supplied password SOLVED: ftp.sh now correctly passes password from command line PROBLEM: server.pem had expired SOLVED: new server.pem valid for ten years PROBLEM: socks notice printed wrong port on some platforms SOLVED: socks now uses correct byte-order for port number in notice further corrections: option name o_trunc corrected to o-trunc combined use of -u and -U is now detected and prevented made message system a little more robust against format string attacks ####################### V 1.2.0.0: new features: address pty for putting socat behind a new pseudo terminal that may fake a serial line, modem etc. experimental openssl integration (it does not provide any trust between the peers because is does not check certificates!) options flock-ex, flock-ex-nb, flock-sh, flock-sh-nb to control all locking mechanism provided by flock() options setsid and setpgid now available with all address types option ctty (controlling terminal) now available for all TERMIOS addresses option truncate (a hybrid of open(.., O_TRUNC) and ftruncate()) is replaced by options o-trunc and ftruncate=offset option sourceport now available with TCP and UDP listen addresses to restrict incoming client connections unidirectional mode right-to-left (-U) solved problems and bugs: PROBLEM: addresses without required parameters but an option containing a '/' were incorrectly interpreted as implicit GOPEN address SOLVED: if an address does not have ':' separator but contains '/', check if the slash is before the first ',' before assuming implicit GOPEN. porting: ptys under SunOS work now due to use of stream options further corrections: with -d -d -d -d -D, don't print debug info during file analysis ####################### V 1.1.0.1: new features: .spec file for RPM generation solved problems and bugs: PROBLEM: GOPEN on socket did not apply option unlink-late SOLUTION: GOPEN for socket now applies group NAMED, phase PASTOPEN options PROBLEM: with unidirectional mode, an unnecessary close timeout was applied SOLUTION: in unidirectional mode, terminate without wait time PROBLEM: using GOPEN on a unix domain socket failed for datagram sockets SOLUTION: when connect() fails with EPROTOTYPE, use a datagram socket further corrections: open() flag options had names starting with "o_", now corrected to "o-" in docu, *-listen addresses were called *_listen address unix now called unix-connect because it does not handle unix datagram sockets in test.sh, apply global command line options with all tests ####################### V 1.1.0.0: new features: regular man page and html doc - thanks to kromJx for prototype new address type "readline", utilizing GNU readline and history libs address option "history-file" for readline new option "dash" to "exec" address that allows to start login shells syslog facility can be set per command line option new address option "tcp-quickack", found in Linux 2.4 option -g prevents option group checking filan and procan can print usage procan prints rlimit infos solved problems and bugs: PROBLEM: raw IP socket SIGSEGV'ed when it had been shut down. SOLVED: set eof flag of channel on shutdown. PROBLEM: if channel 2 uses a single non-socket FD in bidirectional mode and has data available while channel 1 reaches EOF, the data is lost. SOLVED: during one loop run, first handle all data transfers and _afterwards_ handle EOF. PROBLEM: despite to option NONBLOCK, the connect() call blocked SOLVED: option NONBLOCK is now applied in phase FD instead of LATE PROBLEM: UNLINK options issued error when file did not exist, terminating socat SOLVED: failure of unlink() is only warning if errno==ENOENT PROBLEM: TCP6-LISTEN required numeric port specification SOLVED: now uses common TCP service resolver PROBLEM: with PIPE, wrong FDs were shown for data transfer loop SOLVED: retrieval of FDs now pays respect to PIPE pecularities PROBLEM: using address EXEC against an address with IGNOREEOF, socat never terminated SOLVED: corrected EOF handling of sigchld porting: MacOS and old AIX versions now have pty flock() now available on Linux (configure check was wrong) named pipe were generated using mknod(), which requires root under BSD now they are generated using mkfifo further corrections: lots of address options that were "forgotten" at runtime are now available option BINDTODEVICE now also called SO-BINDTODEVICE, IF "make install" now installs binaries with ownership 0:0 ####################### V 1.0.4.2: solved problems and bugs: PROBLEM: EOF of one stream caused close of other stream, giving it no chance to go down regularly SOLVED: EOF of one stream now causes shutdown of write part of other stream PROBLEM: sending mail via socks address to qmail showed that crlf option does not work SOLVED: socks address applies PH_LATE options PROBLEM: in debug mode, no info about socat and platform was issued SOLVED: print socat version and uname output in debug mode PROBLEM: invoking socat with -t and no following parameters caused SIGSEGV SOLVED: -t and -b now check next argv entry PROBLEM: when opening of logfile (-lf) failed, no error was reported and no further messages were printed SOLVED: check result of fopen and print error message if it failed new features: address type UDP-LISTEN now supports option fork: it internally applies socket option SO_REUSEADDR so a new UDP socket can bind to port after `accepting´ a connection (child processes might live forever though) (suggestion from Damjan Lango) ####################### V 1.0.4.1: solved problems and bugs: PROB: assert in libc caused an endless recursion SOLVED: no longer catch SIGABRT PROB: socat printed wrong verbose prefix for "right to left" packets SOLVED: new parameter for xiotransfer() passes correct prefix new features: in debug mode, socat prints its command line arguments in verbose mode, escape special characters and replace unprintables with '.'. Patch from Adrian Thurston. ####################### V 1.0.4.0: solved problems and bugs: Debug output for lstat and fstat said "stat" further corrections: FreeBSD now includes libutil.h new features: option setsid with exec/pty option setpgid with exec/pty option ctty with exec/pty TCP V6 connect test gettimeofday in sycls.c (no use yet) porting: before Gethostbyname, invoke inet_aton for MacOSX ####################### V 1.0.3.0: solved problems and bugs: PROB: test 9 of test.sh (echo via file) failed on some platforms, socat exited without error message SOLVED: _xioopen_named_early(): preset statbuf.st_mode with 0 PROB: test 17 hung forever REASON: child death before select loop did not result in EOF SOLVED: check of existence of children before starting select loop PROB: test 17 failed REASON: child dead triggered EOF before last data was read SOLVED: after child death, read last data before setting EOF PROB: filan showed that exec processes incorrectly had fd3 open REASON: inherited open fd3 from main process SOLVED: set CLOEXEC flag on pty fd in main process PROB: help printed "undef" instead of group "FORK" SOLVED: added "FORK" to group name array PROB: fatal messages did not include severity classifier SOLVED: added "F" to severity classifier array PROB: IP6 addresses where printed incorrectly SOLVED: removed type casts to unsigned short * further corrections: socat catches illegal -l modes corrected error message on setsockopt(linger) option tabdly is of type uint correction for UDP over IP6 more cpp conditionals, esp. for IP6 situations better handling of group NAMED options with listening UNIX sockets applyopts2 now includes last given phase corrected option group handling for most address types introduce dropping of unappliable options (dropopts, dropopts2) gopen now accepts socket and unix-socket options exec and system now accept all socket and termios options child process for exec and system addresses with option pty improved descriptions and options for EXAMPLES printf format for file mode changed to "0%03o" with length spec. added va_end() in branch of msg() changed phase of lock options from PASTOPEN to FD support up to four early dying processes structural changes: xiosysincludes now includes sysincludes.h for non xio files new features: option umask CHANGES file TYPE_DOUBLE, u_double OFUNC_OFFSET added getsid(), setsid(), send() to sycls procan prints sid (session id) mail.sh gets -f (from) option new EXAMPLEs for file creation gatherinfo.sh now tells about failures test.sh can check for much more address/option combinations porting: ispeed, ospeed for termios on FreeBSD getpgid() conditional for MacOS 10 added ranlib in Makefile.in for MacOS 10 disable pty option if no pty mechanism is available (MacOS 10) now compiles and runs on MacOS 10 (still some tests fail) setgroups() conditional for cygwin sighandler_t defined conditionally use gcc option -D_GNU_SOURCE