Hello,

I'm starting this thread to get input from the community about what versions of compilers and other build tools Mbed TLS should support. We of course strive to remain compatible with the latest versions, so this discussion is about support for older versions.

We currently don't really have an official version range for the build dependencies of Mbed TLS:

* C compilers (GCC, Clang, Arm Compiler, IAR, Visual Studio) * Build tools (GNU make, CMake) * Scripting tools (shell, Perl, Python)

In practice, for the past three years or so, most of our continuous integration has been running on Ubuntu 16.04, so we mostly test with GCC 5.4.0, Clang 3.8, GNU make 4.1, CMake 3.5.1 and Python 3.5. (For shell and Perl, even pretty ancient version should work.) For Arm Compiler (armcc/armclang) and IAR, we use the same version as Mbed OS. On Windows, we currently test Visual Studio 2013, 2015 and 2017, as well as a version of Mingw that's changed more quickly than most of the rest of our CI. We also run some tests on FreeBSD (a bit more recent that the Ubuntu machines).

The top-level CMakeLists.txt has conditionals that detect much older versions of CMake, GCC and Clang, but we haven't tested those in ages and we don't really know if, for example, the library still builds with CMake 2.8 and GCC 4.2.

As part of the move of the project from Arm to Trusted Firmware, we'll change our CI infrastructure, and this may or may not mean we end up testing with different versions.

In https://github.com/ARMmbed/mbedtls/issues/2896 I looked at the software versions in some common "slow updating" operating systems: RHEL/Centos, Ubuntu LTS.

1. Is there any interest in the community for making sure that the build keeps (or starts) working on RHEL 6? 2. Is there any interest in the community for making sure that the build keeps working on Ubuntu 16.04? 3. Are there any other "old" platforms that we should consider? 4. Should we consider older compilers (maybe some platforms are stuck with older versions of GCC)? 5. On Windows, what's the oldest version of Visual Studio we should keep compatibility with?

-- Gilles Peskine Mbed TLS developer

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