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

 

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 … )

Continue reading Compatibility GCC Installed

Update to Computer Phosphene Last Night

Yesterday evening, a major software update was received to the computer which I name ‘Phosphene’, putting its Debian version to 9.9 from 9.8. One of the main features of the update was, an update to the NVIDIA graphics drivers, as installed from the standard Debian repositories, to version 390.116.

This allows the maximum OpenGL version supported by the drivers to be 4.6.0, and for the first time, I’m noticing that my hardware now limits me to OpenGL 4.5 .

The new driver version does not come with an update to the CUDA version, the latter of which merits some comment. When users install CUDA to Debian / Stretch from the repositories, they obtain run-time version 8.0.44, even though the newly-updated drivers support CUDA all the way up to version 9. This is a shame because CUDA 8.0 cannot be linked to, when compiling code on the GCC / CPP / C++ 6 framework, that is also standard for Debian Stretch. When we want code to run on the GPGPU, we can just load the code onto the GPU using the CUDA run-time v8.0.44, and it runs fine. But if we want to compile major software against the headers, we are locked out. The current Compiler version is too high, for this older CUDA Run-Time version. (:1) (:4)

But on the other side of this irony, I just performed an extension of my own by installing ‘ArrayFire‘ v3.6.3 , coincidentally directly after this update. And my first attempt to do so involved the binary installer that ships with its own CUDA run-time libraries, those being of version 10. Guess what, Driver version 390 is still not high enough to accommodate Run-Time version 10. This resulted in a confusing error message at first, stating that the driver was not high enough, apparently to accommodate the run-time installed system-wide, which would have been bad news for me, as it would have meant a deeply misconfigured setup – and a newly-botched update. It was only after learning that the binary installer for ArrayFire ships with its own CUDA run-time, that I was relieved to know that the┬ásystem-installed run-time, was fine…

Screenshot_20190429_104916

(Updated 4/29/2019, 20h20 … )

Continue reading Update to Computer Phosphene Last Night

A fact about how software-rendering is managed in practice, today.

People of my generation – and I’m over 50 years old as I’m writing this – first learned about CGI – computer-simulated images – in the form of ‘ray-tracing’. What my contemporaries are slow to find out is that meanwhile, an important additional form of CGI has come into existence, which is referred to as ‘raster-based rendering’.

Ray-tracing has as advantage over raster-based rendering, better optical accuracy, which leads to photo-realism. Ray-tracing therefore still gets used a lot, especially in Hollywood-originated CGI for Movies, etc.. But ray-tracing still has a big drawback, which is, that it’s slow to compute. Typically, ray-tracing cannot be done in real-time, needs to be performed on a farm of computers, and typically, an hour of CPU-time may be needed, to render a sequence which might play for 10 seconds.

But, in order for consumers to be able to play 3D games, the CGI needs to be in real-time, for which reason the other type of rendering was invented in the 1990s, and this form of rendering is carried out by the graphics hardware, in real-time.

What this dichotomy has led to, is model- and scene-editors such as “Blender”, which allow complex editing of 3D content, often with the purpose that the content eventually be rendered by arbitrary, external methods, that include software-based, ray tracing. But such editing applications still themselves possess an Editing Preview window / rectangle, in which their power-users can see the technical details of what they’re editing, in real-time. And those editing preview windows are then hardware-rendered, using raster-based methods, instead of the final result being rendered using raster-based methods.

Continue reading A fact about how software-rendering is managed in practice, today.