As if we didn’t already have enough z/OS C/C++ compilers :)
I've recently been working on Python bindings for z/OS products and wanted to
share some useful notes. IBM recently released the IBM C/C++ for Open
Enterprise Languages on z/OS compiler [1], a free version of IBM Open XL C/C++,
which is a port of LLVM/clang. This compiler can only be used for open source.
For example, to build Python, Node, go packages that require a build phase when
installed or contributing to z/OS open source projects. It's important to note
that the IBM Open XL C/C++ compiler is not compatible with XL C/C++ or xlclang
compilers. This incompatibility may pose challenges. Python 3.11 is developed
using IBM Open XL C/C++, while Python 3.10 uses xlclang. As a result, binary
packages created for Python 3.10 won't work with the IBM Open XL C/C++
compiler.
To overcome this issue, the recommended solution is to build Python
distributions that include the source C/C++ code. During the installation
process using pip, this code can be built. There are a few issues with the new
compiler. Firstly, there is no support for "OS" linkage, meaning no #pragma
linkage(module,OS) or extern 'OS' {}. Custom thunk routines need to be written
to address this. Additionally, the compiler supports inline assembly, but the
-qasmlib=<macro-library> option is not available, making macros unusable. A
workaround I found is to assemble some HLASM code and copy-paste from the
listing.
Moreover, the runtime library is not entirely compatible with XL C/C++. I
discovered that the __amrc structure is missing, which breaks my pzfile package
and makes accessing VSAM files nearly impossible. I plan to open a case with
IBM to address this issue.
Another limitation is that the compiler does not produce source/assembly
listings. Furthermore, thread level storage is not supported, which complicates
the process of porting certain libraries.
On a positive note, IBM has open-sourced their zoslib library [2], which
assists in porting applications to z/OS. There is a lot of useful function in
this library. It supports dynamically loading and calling modules using thunk
routines. Unfortunately, there is a comment in the code which states it only
works with xlclang. The library is Apache 2.0 licensed but it has IBM
copyright. I'm not a lawyer so I'm unsure of the legalities of using this
library for product code.
[1]
https://www.ibm.com/docs/en/cloud-paks/z-modernization-stack/2023.2?topic=languages-cc-open-enterprise-zos
[2] https://github.com/ibmruntimes/zoslib
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to [email protected] with the message: INFO IBM-MAIN
