libzmq/builds/zos/README.md

ZeroMQ on z/OS UNIX System Services

ZeroMQ has been successfully built on z/OS, using z/OS UNIX System Services, a certified UNIX environment for the IBM z-series. The build is possible with the shell scripts in this directory, as described below.

Tested build combinations:

• ZeroMQ 4.0.4, using IBM XL C/C++ compiler, as XPLINK in ILP32 mode

• ZeroMQ 4.0.4, using IBM XL C/C++ compiler, as XPLINK in LP64 mode

(Other combinations are likely to work, possibly with minor changes, but have not been tested.)

There are some minor limitations (detailed below), but all core functionality tests run successfully.

Quickstart on z/OS UNIX System Services

Assuming z/OS UNIX System Services is installed, and the z/OS XL C/C++ compiler suite is installed, ZeroMQ can be built as follows:

• Download and extract ZeroMQ tar file

• Ensure contents of this directory are present at builds/zos within that extracted diretory (eg, zeromq-VERSION/builds/zos/; copy these files in, if not already present, and make sure the shell scripts are executable)

• (Optional) set ZCXXFLAGS for additional compile flags (see below)

• Build the libzmq.a static library with:

  cd zeromq-VERSION
  builds/zos/makelibzmq
  

• (Optional, but recommended) build the core tests with:

  builds/zos/maketests
  

• (Optional, but recommended) run the core tests:

  builds/zos/runtests
  

• To remove built files, to start again (eg, rebuild with different compile/link flags):

  builds/zos/makeclean
  

Compilation flags

To build with optimisation:

• set ZCXXFLAGS to "-O2" before starting build process above

To build with debugging symbols:

• set ZCXXFLAGS to "-g" before starting build process above

To build in 64-bit mode:

The default build is ILP32, the default for the IBM XL C/C++ compiler. To build in LP64 mode (64-bit):

• set ZCXXFLAGS to "-Wc,lp64 -Wl,lp64" before starting build

(64-bit mode can be combined with optimisation or debug symbols.)

Other build flags can be used in ZXCCFLAGS if desired. Beware that they are passed through (Bourne) shell expansion, and passed to both the compile and link stages; some experimentation of argument quoting may be required (and arguments requiring parenthesis are particularly complicated).

ZeroMQ test status on z/OS UNIX System Services

As of 2014-07-22, 41 of the 43 tests in the core ZeroMQ test suite pass. There are two tests that are expected to fail:

0. test_abstract_ipc: tests Linux-specific IPC functions, and is expected to fail on non-Linux platforms.

1. test_fork: tests ability to use ZeroMQ both before and after fork (and before exec()); this relies on the ability to use pthreads both before and after fork. On z/OS (and some other UNIX compliant platforms) functions like pthreads_create (used by ZeroMQ) cannot be used after fork and before exec; on z/OS the call after fork fails with ELEMULTITHREADFORK (errno=257). (On z/OS it appears possible to use z/OS after fork, providing it has not been used before fork -- the problem is the two separate initialisations of the threading library before and after fork attempting to mix together.) In practice this is unlikely to affect many real-world programs -- most programs use threads or fork without exec, but not both.

These two "expected to fail" tests are listed as XFAIL_TESTS, and runtests will still consider the test run successful when they fail as expected.

In addition there are some other minor test issues:

• test_security_curve does not do any meaningful testing, as a result of the CURVE support not being compiled in; it requires libsodium, which has not been ported to z/OS UNIX System Services yet.

• test_monitor will sometimes fail with SIGPIPE (about 1 run in 4); this appears to be a problem with SIGPIPE not being ignored and has been reported upstream.

• test_spec_rep (and possibly other tests) occassionally fail with Resource temporarily unavailable, which is a result of EAGAIN not being properly caught in all places and the function call retried. This has also been reported upstream.

ZeroMQ on z/OS UNIX System Services: Portability notes

*.cpp

The source code in ZeroMQ is a combination of a C++ core library (in *.cpp and *.hpp files), and a C wrapper (also in *.cpp files). It is all compiled with the C++ compiler. The IBM XL C/C++ complier (at least the version used for initial porting) insists that C++ source be in *.C files (note capital C). To work around this issue the compile flag -+ is used (specified in the zc++ compiler wrapper), which tells the compiler the file should be considered C++ despite the file extension.

XPLINK

The library (and tests) are built in XPLINK mode with the flags -Wc,xplink -Wl,xplink (specified in the zc++ compiler wrapper). This is recommended by IBM for C++ code due to the small functions. (Amongst other things, using XPLINK enables function calls with some arguments passed in registers.)

long long

ZeroMQ makes use of uint64_t (which is unsigned long long in ILP32 mode). To enable this the compile flag -Wc,lang(longlong) is passed to enable long long. This is passed from the zc++ compiler wrapper in order to be able to specifically quote the argument to protect the parentheses from shell expansion.

BSD-style sockets, with IPv6 support

ZeroMQ uses BSD-style socket handling, with extensions to support IPv6. BSD-style sockets were merged into SysV-derived UNIX at least a decade ago, and are required as part of the X/Open Portability Guide at least as of XPG 4.2. To access this functionality two feature macros are defined:

• _XOPEN_SOURCE_EXTENDED=1

• _OPEN_SYS_SOCK_IPV6

The first enables the XPG 4.2 features (including functionality like getsockname()), and the latter exposes IPv6 specific functionality like sa_family_t. These flags are defined in the cxxall script.

(The traditional BSD-sockets API, exposed with _OE_SOCKETS cannot be used because it does not support functions like getsockname(), nor does it support IPv6 -- and the API definitions prevent compiling in LP64 mode due to assumptions about long being 32 bits. Using _XOPEN_SOURCE_EXTENDED=1 avoids all these problems.)

pthreads

ZeroMQ uses the pthreads library to create additional threads to handle background communication without blocking the main application. This functionaity is enabled on z/OS UNIX System Services by defining:

• _OPEN_THREADS=3

which is done in the cxxall script. (The "3" value exposes later pthreads functionality like pthread_atfork, although ZeroMQ does not currently use all these features.)

platform.hpp on z/OS UNIX System Services

The build (described above) on z/OS UNIX System Services uses a static pre-built platform.hpp file. (By default src/platform.hpp is dynamically generated as a result of running the ./configure script.) The master version of this is in builds/zos/platform.hpp.

The pre-built file is used because z/OS does not have the GNU auto tools (automake, autoconf, libtool, etc) installed, and particularly the libtool replacement does not work properly with the IBM XL C/C++ compiler.

The ./configure script (only supplied in the tarballs); built with automake and autoconf on another platform), with one small edit, was used to generate the z/OS platform.hpp and then two small changes (described below) were made by hand to the generated platform.hpp.

To be able to run the ./configure script to completion (in tcsh syntax):

• Edit ./configure and add:

  openedition)
        ;;
  

  immediately before the line:

  as_fn_error $? "unsupported system: ${host_os}." "$LINENO" 5
  

  (somewhere around 17637). This avoids the configure script giving up early because openedition is not recognised.

• set CXX to point that the full path to the builds/zos/zc++ wrapper, eg

  setenv CXX "/u/0mq/zeromq-4.0.4/builds/zos/zc++"
  

• set CPPFLAGS to for the feature macros required, eg:

  setenv CPPFLAGS "-D_XOPEN_SOURCE_EXTENDED=1 -D_OPEN_THREADS=3 -D_OPEN_SYS_SOCK_IPV6"
  

• set CXXFLAGS to enable XPLINK:

  setenv CXXFLAGS "-Wc,xplink -Wl,xplink -+"
  

• run configure script with --disable-eventfd (sys/eventfd.h does not exist, but the test for its existance has a false positive on z/OS UNIX System Services, apparently due to the way the c++ compiler wrapper passes errors back from the IBM XL C/C++ compiler), viz:

  ./configure --disable-eventfd
  

All going well several Makefiles, and src/platform.hpp should be produced. Two additional changes are required to src/platform.hpp which can be appended to the end:

/* ---- Special case for z/OS Unix Services: openedition ---- */
#include <pthread.h>
#ifndef   NI_MAXHOST
#define   NI_MAXHOST 1025
#endif

(many includes require pthreads-related methods or data structures to be defined, but not all of them include pthread.h, and the value NI_MAXHOST is not defined on z/OS UNIX System Services -- the 1025 value is the conventional value on other platforms).

Having done this the Makefiles can be used to compile individual files if desired, eg:

cd src
make zmq.o

but note:

• IBM Make will warn of duplicate prerequisites on every run of make, and both the generated src/Makefile and tests/Makefile have several duplicates. (For src/Makefile edit libzmq_la_SOURCES to remove the duplicates.)

• IBM Make does not understand the @ prefix (eg, @echo) as a way to avoid echoing the command, resulting in an error and the command being echoed anyway.

• Many of the make targets result in GNU auto tools (aclocal, etc) being invoked, which are likely to fail, and most of the library-related targets will invoke libtool which will cause compile failures (due to differences in expected arguments).

However running ./configure to regenerate src/platform.hpp may be useful for later versions of ZeroMQ which add more feature tests.