## My system for switching between compilers needed an overhaul.

According to what I had written in earlier postings, I had co-installed a Debian Jessie / Security version of the GCC / CPP / C++ compiler system, which had version 4.9.2, alongside the official versions, which were 6.3, on the Debian / Stretch computer I name ‘Phosphene’. There was a problem in how I had done that. If next, the Package Maintainers had pushed through an update to their official compiler, the update would have broken my link groups – in a devastating way. And so what I needed to do was to rearrange those link-groups, to make them compatible with this scenario. The result is as follows:


dirk@Phosphene:~$su Password: root@Phosphene:/home/dirk# update-alternatives --config cc There are 2 choices for the alternative cc (providing /usr/bin/cc). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/bin/gcc 20 auto mode 1 /usr/bin/gcc 20 manual mode 2 /usr/bin/gcc-4.9 10 manual mode Press to keep the current choice[*], or type selection number: root@Phosphene:/home/dirk# update-alternatives --config cpp There are 2 choices for the alternative cpp (providing /lib/cpp). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/bin/cpp 20 auto mode 1 /usr/bin/cpp 20 manual mode 2 /usr/bin/cpp-4.9 10 manual mode Press to keep the current choice[*], or type selection number: root@Phosphene:/home/dirk# update-alternatives --config c++ There are 2 choices for the alternative c++ (providing /usr/bin/c++). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/bin/g++ 20 auto mode 1 /usr/bin/g++ 20 manual mode 2 /usr/bin/g++-4.9 10 manual mode Press to keep the current choice[*], or type selection number: root@Phosphene:/home/dirk# ls -l /usr/bin/gcc lrwxrwxrwx 1 root root 5 May 3 10:58 /usr/bin/gcc -> gcc-6 root@Phosphene:/home/dirk# ls -l /usr/bin/cpp lrwxrwxrwx 1 root root 5 May 3 11:01 /usr/bin/cpp -> cpp-6 root@Phosphene:/home/dirk# ls -l /usr/bin/g++ lrwxrwxrwx 1 root root 5 May 3 11:24 /usr/bin/g++ -> g++-6 root@Phosphene:/home/dirk# exit exit dirk@Phosphene:~$



Dirk Mittler

## ArrayFire 3.5.1 Compiled, using GCC 4.9.2 and CUDA – Success!

A project which has fixated me for several days has been, to get the API which is named “ArrayFire” custom-compiled, specifically version 3.5.1 of that API, to enable CUDA support. This poses a special problem because when we use the Debian / Stretch repositories to install the CUDA Run-Time, we are limited to installing version 8.0.44. This run-time is too old, to be compatible with the standard GCC / CPP / C++ compiler-set available under the same distribution of Linux. Therefore, it can be hard for users and Debian Maintainers alike to build projects that use CUDA, and which are compatible with -Stretch.

Why use ArrayFire? Because writing kernels for parallel computing on the GPU is hard. ArrayFire is supposed to make the idea more-accessible to people like me, who have no specific training in writing highly parallel code.

When we install ArrayFire from the repositories, OpenCL support is provided, but not CUDA support.

I’ve hatched a plan by which I can install an alternative compiler set on the computer I name ‘Phosphene’, that being GCC / CPP / C++ version 4.9.2, and with which I can switch my compilers to that version, so that maybe, I can compile projects in the future, that do use CUDA, and that are sophisticated enough to require a full compiler-suite to build.

What I’ve found was that contrarily to how it went the previous time, this time I’ve scored a success.   Not only did the project compile without errors, but then, a specific Demo that ships with the source-code version, that uses the ability of CUDA to pass graphics to the OpenGL rendering of the GPU, also ran without errors…

So now I can be sure that the tool-chain which I’ve installed, is up to the task of compiling highly-complex CUDA projects.

(Update 5/03/2019, 7h30 : )

## Compatibility GCC Installed

One of the more frustrating facts about Debian / Stretch is that its maintainers have broken with tradition, by no longer providing any compatibility versions of the main compilers, GCC, CPP and C++, which provide CC and C++ -language support, useful in 90% (+) of all programming that takes place. Instead, Debian / Stretch provides GCC / CPP / C++ version 6.3 alone. What I had already written about was, that the version of the CUDA Run-Time and Toolkit available from the standard repositories, has remained v8.0.44 for the time being. This CUDA Version does not support CC or C++ version 6 because version 6 of these compilers is too high!

One way in which power-users could try to remedy this situation would be, to install some sort of compatibility version of CC / C++, even though none is offered in the standard repositories. But, when we try to custom-compile let’s say, GCC v5.3, which would already be low enough for CUDA 8.0.44 to support, we find that GCC 6.3 is just plain unable to compile GCC 5.3, no matter what.

And so another way to solve the same problem can be, to add the old Debian Jessie / Oldstable repositories to our sources list, and then just to install from there.

I find this to be an extremely bad idea.

First of all, Debian differs from Ubuntu, in that Debian never provided GCC 5.3. In Debian / Jessie, what we got was GCC 4.8, or maybe even v4.9. But more importantly, simply sandwiching two incompatible repositories together can create a fatal set of problems.

What I was finally able to do, was just to download roughly a dozen packages as binaries, from the Debian Repository Web-site, which finally provided GCC, CPP and C++ v4.8. The path I took required that I run into the error message numerous times that dependencies could not be satisfied, because under Debian, neither ‘/usr/bin/gcc’ nor ‘/usr/bin/c++’ are provided by a single, binary package. Each is provided by packages, that depend uniquely on other packages, that are also not in the repositories.

Further, once the power-user has in fact installed binaries, after making sure that none of their file-names overlap, he must also create a system of Debian Alternatives, that allow him to switch between compilers easily. The problem with that is the fact that because, under Debian / Stretch, no provision was ever made by Package Maintainers for alternatives to exist, automatic mechanisms have also not been provided, to install ‘Link Groups’. The Link Groups ‘cc’, ‘cpp’ and ‘c++’ exist, but only in such a way as to provide one executable each.

As I was doing my best to install the Link Groups, I made a mistake, which simply over-wrote ‘/usr/bin/gcc’ with a different symlink, and which therefore forced me to (1) delete the link-group, and (2) reinstall GCC 6.3 from the package manager. After that, a new attempt to set up the link-groups succeeded:


dirk@Phosphene:~$su Password: root@Phosphene:/home/dirk# update-alternatives --config cc There are 2 choices for the alternative cc (providing /usr/bin/cc). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/bin/gcc-6 20 auto mode 1 /usr/bin/gcc-4.8 10 manual mode 2 /usr/bin/gcc-6 20 manual mode Press to keep the current choice[*], or type selection number: root@Phosphene:/home/dirk# update-alternatives --config cpp There are 2 choices for the alternative cpp (providing /usr/bin/cpp). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/bin/cpp-6 20 auto mode 1 /usr/bin/cpp-4.8 10 manual mode 2 /usr/bin/cpp-6 20 manual mode Press to keep the current choice[*], or type selection number: root@Phosphene:/home/dirk# update-alternatives --config c++ There are 2 choices for the alternative c++ (providing /usr/bin/c++). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/bin/g++-6 20 auto mode 1 /usr/bin/g++-4.8 10 manual mode 2 /usr/bin/g++-6 20 manual mode Press to keep the current choice[*], or type selection number: root@Phosphene:/home/dirk# exit exit dirk@Phosphene:~$



Note: The first link above, named ‘cc’, has a corresponding slave-link named ‘gcc’, thereby forming the only real ‘Link Group’. The others are just plain Links.

I am reasonably certain that none of these link-groups are broken. But what my reader should be able to infer from what I’ve written, is that It would be a hare-brained attempt, to duplicate what I’ve done, entirely based on this blog posting.

(Edit 5/03/2019, 11h45 : )

Just to prove how hare-brained this idea really is, I just uninstalled the alternative compilers, and replaced them with the GCC / CPP / C++ tool-chain, version 4.9, and made that part of the update-alternatives system as above! (:3)

(End of Edit.)

So what does this provide me with (hopefully)?

(Updated 5/02/2019, 12h15 … )