Context

I recently installed Ubuntu 18.04, Linux foobar-VirtualBox 4.15.0-23-generic #25-Ubuntu SMP Wed May 23 18:02:16 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux on a VM. I want to cross-compile applications for Cortex-M4F CPUs with hard floating points, and therefore I have installed the package gcc-arm-none-eabi version 15:6.3.1+svn253039-1build1 as well as libnewlib-arme-none-eabi at version 2.4.0.20160527-3.

Problem

There is a linker error due to a conflict between my object files using hard floats and the libraries using soft floats. Some research indicates that this is a known Ubuntu 18.04 (Bionic Beaver) issue:

• Debian issue
• gcc ARM Embedded team issue

Note that I do provide the correct compiler and linker flags, and this project correctly builds with the Windows cross-toolchain from GNU ARM Embedded. I think it'd be pointless to paste the complete error here. If someone thinks it'd be required I'd be glad to edit this question.

What I already tried

From my basic understanding, I have two solutions to get a functional GCC ARM toolchain:

1. Downgrade gcc-arm-none-eabi to return to a working version
2. Remove gcc-arm-none-eabi and install instead gcc-arm-embedded from the team GCC ARM embedded's PPA (Install gcc-arm-embedded from the PPA)

Downgrading gcc-arm-none-eabi, but to what?

In order to downgrade gcc-arm-none-eabi I have to find a previous version in my package manager. I first updated the package list with sudo apt update, then I typed:

sudo apt show gcc-arm-none-eabi

Package: gcc-arm-none-eabi
Version: 15:6.3.1+svn253039-1build1
Priority: extra
Section: universe/devel
Origin: Ubuntu
Maintainer: Ubuntu Developers
Original-Maintainer: Agustin Henze
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 307 MB
Depends: libc6 (>= 2.15), libgcc1 (>= 1:3.0), libgmp10, libisl15 (>= 0.15), libmpc3, libmpfr6 (>= 3.1.3), libstdc++6 (>= 5), zlib1g (>= 1:1.1.4), binutils-arm-none-eabi
Recommends: libnewlib-arm-none-eabi
Homepage: http://gcc.gnu.org/
Download-Size: 24.3 MB
APT-Sources: http://ch.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
Description: GCC cross compiler for ARM Cortex-A/R/M processors
Bare metal compiler for embedded ARM chips using Cortex-M, Cortex-R and
Cortex-A processors.
This package is based on the GNU ARM toolchain provided by ARM.

There, I don't see any previous version. I think they should be listed here, but I don't see it. I can't downgrade if I can't provide the exact previous version I want to downgrade to.

Using gcc-arm-embedded instead of gcc-arm-none-eabi

I followed the instructions given in the link above, which led me to these commands:

sudo apt remove gcc-arm-none-eabi
sudo apt-add-repository ppa:team-gcc-arm-embedded/ppa
sudo apt update

[…] Ign:4 http://ppa.launchpad.net/team-gcc-arm-embedded/ppa/ubuntu bionic InRelease
Get:5 http://security.ubuntu.com/ubuntu bionic-security InRelease [83.2 kB]
Err:6 http://ppa.launchpad.net/team-gcc-arm-embedded/ppa/ubuntu bionic Release
404 Not Found [IP: 91.189.95.83 80]
Reading package lists… Done
E: The repository 'http://ppa.launchpad.net/team-gcc-arm-embedded/ppa/ubuntu bionic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

sudo apt-install gcc-arm-embedded

Reading package lists… Done
Building dependency tree
Reading state information… Done
E: Unable to locate package gcc-arm-embedded

Basically it seems I have issues accessing the PPA. I tried the apt switch --allow-unauthenticated, but it didn't change the commands output.

Question

Is there a way to make one of those two solutions work, or is there another way to get a functional GCC toolchain on Ubuntu 18.04 to build hard-float application for the Cortex-M4F CPU?

(I've recently posted a Stack Overflow question on this issue, as at this time I thought it was a toolchain issue not so related with the Unix world. If I get an answer here I'll close it and redirect to this Q/A)