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](http://www-03.ibm.com/systems/z/os/zos/features/unix/),
a certified UNIX environment for the [IBM
z-series](http://www-03.ibm.com/systems/z/).  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](http://www-03.ibm.com/systems/z/os/zos/features/unix/) is
installed, and the [z/OS XL C/C++
compiler suite](http://www-03.ibm.com/software/products/en/czos) 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](http://publib.boulder.ibm.com/infocenter/zvm/v6r1/index.jsp?topic=/com.ibm.zos.r9.cbcux01/lp64cop.htm),
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.

0.  `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`](http://doc.libsodium.org/), 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](http://www.redbooks.ibm.com/abstracts/sg245991.html) mode
with the flags `-Wc,xplink -Wl,xplink` (specified in  the `zc++`
compiler wrapper).  This is [recommended by IBM for C++
code](http://publib.boulder.ibm.com/infocenter/zvm/v5r4/index.jsp?topic=/com.ibm.zos.r9.ceea200/xplrunt.htm)
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.