I recently tested the new Raspberry Pi OS called Trixie and I saw they are using a very recent version of the GCC compiler version:

pi@trixie2:~/mystuff/immediatec/src $ gcc-14 --version

gcc-14 (Debian 14.2.0-19) 14.2.0

Copyright (C) 2024 Free Software Foundation, Inc.

This is free software; see the source for copying conditions.  There is NO

warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

But what if you want to use an older version of GCC, say, version 10?

It's possible to have more than one GCC compiler on your Linux (so, also Raspberry Pi) distro.  Here's how to do it.

First of all, as you can see on the command I gave before, I had to type gcc-14 to know the version of the default GCC compiler for Trixie.  

But if GCC version 14 is the default GCC compiler for Trixie, why did I have to type gcc-14 and not just gcc?  Well, I already installed gcc-10 too and made that one the default GCC compiler.

So, if I type gcc --version, I get the following on my Raspberry Pi system:

pi@trixie2:~/mystuff/immediatec/src $ gcc --version

gcc (Debian 10.2.1-6) 10.2.1 20210110

Copyright (C) 2020 Free Software Foundation, Inc.

This is free software; see the source for copying conditions.  There is NO

warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

This is the - currently default - GCC compiler version 10.

Of course, I could also have typed gcc-10 --version.  That would have returned exactly the same result.

Adding an older compiler

To add an older compiler, you first have to decide what compiler you want.  In my case, I wanted the same compiler that was use on the Raspberry Pi OS Bullseye.  The GCC compiler version used for Bullseye was 10.2.1-6.

The less intruding way is to download all related .deb files from the Debian snapshot archive or Debian packages site.

The latter on (Debian package site) is the easiest one to me.

Best practice: create a directory on the computer where you put all GCC 10 related files (before you copy them to the Raspberry Pi).

Go to the package site and go to the bottom of the page. Then click the arm64 link which will bring you to the download page itself.  Select an FTP site of your choice and the download should start.  Always verify the checksum if you have the chance to do so.

Here is a list (including links) of all the .deb files you need to get the complete GCC version 10 compiler:

• gcc-10-base (arm64, Bullseye)

• gcc-10 (arm64, Bullseye)

• g++-10 (arm64, Bullseye)

• cpp-10 (arm64, Bullseye)

• libgcc-10-dev (arm64, Bullseye)

• libstdc++-10-dev (arm64, Bullseye)

• libasan6 (arm64, Bullseye)

• libtsan0 (arm64, Bullseye)

Once all of the above .deb files are downloaded, move/copy them to a dedicated directory on the Raspberry Pi.

If all are available on the Raspberry Pi, run the following two commands from within that dedicated directory:

sudo dpkg -i *.deb

sudo apt -f install

The first command will install all the .deb files, the second command will fix any remaining dependency, should there be one or more...

Setting the default compiler of your choice

Once the GCC 10 compiler is installed, it can be used next to the default GCC 14 compiler.  

You can each and every time run the command gcc-10 ... or gcc-14 ... but that's a bit cumbersome.

You can also run the update-alternative command (just like you can for different flavours of Java).  Therefore, you first have to install the two compiler versions like so:

• For the GCC compiler
  
  

sudo update-alternatives --install /user/bin/gcc gcc /usr/bin/gcc-10 10
sudo update-alternatives --install /user/bin/gcc gcc /usr/bin/gcc-14 14
sudo update-alternatives --config gcc

The last command is to choose your default GCC compiler.  You will see a list and numbers.  Choose the number next to the compiler you want as default.

• For the G++ compiler
  
  

sudo update-alternatives --install /user/bin/g++ g++ /usr/bin/g++-10 10
sudo update-alternatives --install /user/bin/g++ g++ /usr/bin/g++-14 14
sudo update-alternatives --config g++

The last command is to choose your default G++ compiler.  You will see a list and numbers.  Choose the number next to the compiler you want as default.

It looks like this when running the --config command:

pi@trixie2:~/mystuff/immediatec/src $ sudo update-alternatives --config g++

There are 2 choices for the alternative g++ (providing /usr/bin/g++).

  Selection    Path             Priority   Status

------------------------------------------------------------

  0            /usr/bin/g++-14   14        auto mode

* 1            /usr/bin/g++-10   10        manual mode

  2            /usr/bin/g++-14   14        manual mode

Press <enter> to keep the current choice[*], or type selection number:

You can keep the current choice by pressing Enter or you can change it by typing a number.  Here, it can be 0, 1 or 2.

Same mechanism is used for the GCC compiler above.

Check if you're using GCC in 64 bit mode

To know if the GCC compiler is using 64-bit mode, run the following command:

gcc-10 -dM -E - < /dev/null | grep __SIZEOF_INT128__

or

gcc-14 -dM -E - < /dev/null | grep __SIZEOF_INT128_

You should see #define __SIZEOF_INT128__ 16 if it does.

I recently had problems to find out which include files were taken into account when looking at one of the immediateC files named icg.h

To be able to do that, you can ask the GCC compiler to only preprocess the file and not compile it.  You do have to specify a -o parameter but you have to reroute it to /dev/null.  If you don't pass the -o flag, GCC just spits out pages of gibberish.

Since the output is not sent to stdout but to stderr, you have to apply the special 2> construction if you want to get the output written to a file.

The complete command is:

gcc -E -H <file> -o /dev/null 2> <output_file>

Example:

gcc -E -H icg.h -o /dev/null 2> header_flow.txt

Once the file is generated, you can nicely see what include files are used and how they're related to each other.  Every new include level is represented by a . (dot) like so:

pi@trixie2:~/mystuff/immediatec/src $ gcc -E -H /usr/local/include/icg.h -o /dev/null 2> output.txt

. /usr/include/signal.h

.. /usr/include/features.h

... /usr/include/features-time64.h

.... /usr/include/aarch64-linux-gnu/bits/wordsize.h

.... /usr/include/aarch64-linux-gnu/bits/timesize.h

... /usr/include/aarch64-linux-gnu/sys/cdefs.h

.... /usr/include/aarch64-linux-gnu/bits/wordsize.h

.... /usr/include/aarch64-linux-gnu/bits/long-double.h

... /usr/include/aarch64-linux-gnu/gnu/stubs.h

.... /usr/include/aarch64-linux-gnu/bits/wordsize.h

.... /usr/include/aarch64-linux-gnu/gnu/stubs-lp64.h

.. /usr/include/aarch64-linux-gnu/bits/types.h

First level has one dot, second level two dots and so on...

This way, it's very easy to see how the include tree is going for the given file.

Note that the file you pass to the gcc command can be a header file or a C file.