How to Install compiler g++-4.8.5 in ubuntu 20.04 - c++

Question

As the title said I can't install that specific version of g++ in my current ubuntu (20.04).
I have been trying the usual things as: sudo apt install g++- (and displaying all posibilities but there where only versions from 8 to 10). Same happend looking for gcc possibilities.
Also tried this: gist.github.com/application2000/73fd6f4bf1be6600a2cf9f56315a2d91 (same problem)
And after looking for a while I gave up in my research and ended up here. Hope someone with more wisdom than me can give my a hand with this.

Answer 1

These steps should work:
sudo dpkg --add-architecture i386
sudo apt update
sudo apt upgrade
sudo apt-get install gcc-multilib libstdc++6:i386
wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.5/gcc-4.8.5.tar.bz2 --no-check-certificate
tar xf gcc-4.8.5.tar.bz2
# cd gcc-4.8.5
# ./contrib/download_prerequisites
# cd ..
sed -i -e 's/__attribute__/\/\/__attribute__/g' gcc-4.8.5/gcc/cp/cfns.h
sed -i 's/struct ucontext/ucontext_t/g' gcc-4.8.5/libgcc/config/i386/linux-unwind.h
mkdir xgcc-4.8.5
pushd xgcc-4.8.5
$PWD/../gcc-4.8.5/configure --enable-languages=c,c++ --prefix=/usr --enable-shared --enable-plugin --program-suffix=-4.8.5
make MAKEINFO="makeinfo --force" -j
sudo make install -j
Note that you have to uncomment the .../download_prerequisites on some platform. For me it worked without on Centos 7 or Ubuntu 20 with the mandatory packages installed:
Ubuntu/Debian:
sudo apt install make wget git gcc g++ lhasa libgmp-dev libmpfr-dev libmpc-dev flex bison gettext texinfo ncurses-dev autoconf rsync
Centos:
sudo yum install wget gcc gcc-c++ python git perl-Pod-Simple gperf patch autoconf automake make makedepend bison flex ncurses-devel gmp-devel mpfr-devel libmpc-devel gettext-devel texinfo
Few seconds later (/giggles) gcc-4.8.5 is installed and available.
Notes:
if you don't have the resources to run make -j omit -j or use -j4 (or a different number which is adequate for your system)
your milage may vary and you may need to install further i386 packages

Answer 2

Since I can't comment I will add to #bebbo solution that on an Ubuntu 20.04 I had to add to his steps patching the following patches:
Add an include to signal.h to libsanitizer/asan/asan_linux.cc
https://patchwork.ozlabs.org/project/gcc/patch/6824253.3U2boEivI2#devpool21/
change a line in libsanitizer/tsan/tsan_platform_linux.cc
as shown. line number may not be the one stated in the patch so search for the line that was changed. There is no need to apply the patch to the other files
https://git.pantherx.org/mirror/guix/commit/0b93d04ac537d6413999349ebe7cdcb1e961700e

Answer 3

Adding to kpeace's answer...
sed -i '/#include <pthread.h>/a #include <signal.h>' path_to_gcc4.8.5src/libsanitizer/asan/asan_linux.cc
sed -i 's/__res_state \\*statp = (__res_state\\*)state\\;/struct __res_state \\*statp = (struct __res_state\\*)state\\;/g' path_to_gcc4.8.5src/libsanitizer/tsan/tsan_platform_linux.cc
Just adding a couple of sed lines to patch them inline.
Also, I've been writing some Ruby scripts to install some software (for fun of course.) I've recently successfully compiled gcc-4.8.5 under LinuxMint 20.1 (Ubuntu 20.04 based, compiler is the system gcc: 9.3.0, installed with sudo apt install build-essential) with this script. Also, I've installed all the packages that Bebbo suggested, including gcc-multilib and libstdc++6:i386 before running this script. Check up InstGcc4 class at the bottom of the code.
install_gcc.rb
They might end up to be 'un-installable' state a few months later. But at least gcc-4.8.5 works now.
ps. I've started to compile this old gcc due to CUDA... My hardware is a decade old GeForce 9600/9400 (yeah 2008 MBP) and CUDA 6.5 was the best option for that machine.
pps. Anyway, strange thing is, I had to give out '-std=gnu++11' for CXXFLAGS to avoid errors.