diff --git a/build/bin/write-dockerfile.sh b/build/bin/write-dockerfile.sh
index a7d23ba9689..854f0285967 100755
--- a/build/bin/write-dockerfile.sh
+++ b/build/bin/write-dockerfile.sh
@@ -53,6 +53,12 @@ EOF
         UPDATE="$SUDO apt-get update &&"
         INSTALL="$SUDO DEBIAN_FRONTEND=noninteractive apt-get install -qqq --no-install-recommends --yes"
         CLEAN="&& $SUDO apt-get clean"
+        if [ -n "$EXTRA_REPOSITORY" ]; then
+            cat <<EOF
+RUN $UPDATE $INSTALL software-properties-common && ($INSTALL gpg gpg-agent || echo "(ignored)")
+RUN $SUDO add-apt-repository $EXTRA_REPOSITORY
+EOF
+        fi
         ;;
     fedora*|redhat*|centos*)
         cat <<EOF
diff --git a/build/pkgs/_gcc10/distros/debian.txt b/build/pkgs/_gcc10/distros/debian.txt
new file mode 100644
index 00000000000..d08103a678d
--- /dev/null
+++ b/build/pkgs/_gcc10/distros/debian.txt
@@ -0,0 +1,3 @@
+gcc-10
+g++-10
+gfortran-10
diff --git a/build/pkgs/_gcc10/distros/homebrew.txt b/build/pkgs/_gcc10/distros/homebrew.txt
new file mode 100644
index 00000000000..e05f1361b9d
--- /dev/null
+++ b/build/pkgs/_gcc10/distros/homebrew.txt
@@ -0,0 +1 @@
+gcc@10
diff --git a/build/pkgs/_gcc10/type b/build/pkgs/_gcc10/type
new file mode 100644
index 00000000000..134d9bc32d5
--- /dev/null
+++ b/build/pkgs/_gcc10/type
@@ -0,0 +1 @@
+optional
diff --git a/build/pkgs/_gcc11/distros/debian.txt b/build/pkgs/_gcc11/distros/debian.txt
new file mode 100644
index 00000000000..f3fc6a089b2
--- /dev/null
+++ b/build/pkgs/_gcc11/distros/debian.txt
@@ -0,0 +1,3 @@
+gcc-11
+g++-11
+gfortran-11
diff --git a/build/pkgs/_gcc11/distros/homebrew.txt b/build/pkgs/_gcc11/distros/homebrew.txt
new file mode 100644
index 00000000000..992bd1407d1
--- /dev/null
+++ b/build/pkgs/_gcc11/distros/homebrew.txt
@@ -0,0 +1 @@
+gcc@11
diff --git a/build/pkgs/_gcc11/type b/build/pkgs/_gcc11/type
new file mode 100644
index 00000000000..134d9bc32d5
--- /dev/null
+++ b/build/pkgs/_gcc11/type
@@ -0,0 +1 @@
+optional
diff --git a/build/pkgs/_gcc12/distros/debian.txt b/build/pkgs/_gcc12/distros/debian.txt
new file mode 100644
index 00000000000..1621205480f
--- /dev/null
+++ b/build/pkgs/_gcc12/distros/debian.txt
@@ -0,0 +1,3 @@
+gcc-12
+g++-12
+gfortran-12
diff --git a/build/pkgs/_gcc12/distros/homebrew.txt b/build/pkgs/_gcc12/distros/homebrew.txt
new file mode 100644
index 00000000000..253faeebe4a
--- /dev/null
+++ b/build/pkgs/_gcc12/distros/homebrew.txt
@@ -0,0 +1 @@
+gcc@12
diff --git a/build/pkgs/_gcc12/type b/build/pkgs/_gcc12/type
new file mode 100644
index 00000000000..134d9bc32d5
--- /dev/null
+++ b/build/pkgs/_gcc12/type
@@ -0,0 +1 @@
+optional
diff --git a/build/pkgs/_gcc9/distros/debian.txt b/build/pkgs/_gcc9/distros/debian.txt
new file mode 100644
index 00000000000..94f27165784
--- /dev/null
+++ b/build/pkgs/_gcc9/distros/debian.txt
@@ -0,0 +1,3 @@
+gcc-9
+g++-9
+gfortran-9
diff --git a/build/pkgs/_gcc9/distros/homebrew.txt b/build/pkgs/_gcc9/distros/homebrew.txt
new file mode 100644
index 00000000000..c8f32320ba5
--- /dev/null
+++ b/build/pkgs/_gcc9/distros/homebrew.txt
@@ -0,0 +1 @@
+gcc@9
diff --git a/build/pkgs/_gcc9/type b/build/pkgs/_gcc9/type
new file mode 100644
index 00000000000..134d9bc32d5
--- /dev/null
+++ b/build/pkgs/_gcc9/type
@@ -0,0 +1 @@
+optional
diff --git a/src/doc/en/developer/portability_testing.rst b/src/doc/en/developer/portability_testing.rst
index 528bbfaff1b..ad4b5521ffa 100644
--- a/src/doc/en/developer/portability_testing.rst
+++ b/src/doc/en/developer/portability_testing.rst
@@ -55,6 +55,10 @@ To get started, you need to install a `Docker client
 Linux, Mac, and Windows.  The clients for the latter are known as
 "Docker Desktop".
 
+Make sure that your Docker client is configured to provide enough RAM
+to the containers (8 GB are a good choice). In Docker Desktop this
+setting is in Preferences -> Resources -> Advanced.
+
 All examples in this section were obtained using Docker Desktop for
 Mac; but the `command-line user interface
 <https://docs.docker.com/engine/reference/commandline/cli/>`_ for the
diff --git a/tox.ini b/tox.ini
index da672524b8a..3deae3e6cb9 100644
--- a/tox.ini
+++ b/tox.ini
@@ -191,6 +191,7 @@ setenv =
     #
     ubuntu:         SYSTEM=debian
     ubuntu:         BASE_IMAGE=ubuntu
+    ubuntu-toolchain:                        EXTRA_REPOSITORY=ppa:ubuntu-toolchain-r/test
     ubuntu-trusty:    BASE_TAG=trusty
     ubuntu-trusty:                             IGNORE_MISSING_SYSTEM_PACKAGES=yes
     ubuntu-xenial:    BASE_TAG=xenial
@@ -530,8 +531,13 @@ setenv =
     #
     gcc_spkg:                 CONFIG_CONFIGURE_ARGS_2=--without-system-gcc
     gcc_9:                    CONFIG_CONFIGURE_ARGS_2=--with-system-gcc=force CC=gcc-9 CXX=g++-9 FC=gfortran-9
+    gcc_9:                      EXTRA_SAGE_PACKAGES_2=_gcc9
     gcc_10:                   CONFIG_CONFIGURE_ARGS_2=--with-system-gcc=force CC=gcc-10 CXX=g++-10 FC=gfortran-10
+    gcc_10:                     EXTRA_SAGE_PACKAGES_2=_gcc10
     gcc_11:                   CONFIG_CONFIGURE_ARGS_2=--with-system-gcc=force CC=gcc-11 CXX=g++-11 FC=gfortran-11
+    gcc_11:                     EXTRA_SAGE_PACKAGES_2=_gcc11
+    gcc_12:                   CONFIG_CONFIGURE_ARGS_2=--with-system-gcc=force CC=gcc-12 CXX=g++-12 FC=gfortran-12
+    gcc_12:                     EXTRA_SAGE_PACKAGES_2=_gcc12
     llvm:                     CONFIG_CONFIGURE_ARGS_2=--with-system-gcc=force CC=clang CXX=clang++
     llvm:                       EXTRA_SAGE_PACKAGES_2=llvm
     # LLVM is keg-only