setup-build-env: fix cross-compilation dependencies

BPF CI got broken due to apt errors when installing cross compilers:
* https://github.com/kernel-patches/bpf/actions/runs/14519065074/job/40735249827

dpkg --add-architecture now breaks apt config. Looks like there were
changes in Ubuntu that require migrating to deb822 [1][2] format of
apt package lists.

In our case not only target arch repos need to be added, but also
default /etc/apt/sources.list.d/ubuntu.sources needs to be modified.
The host architecture has to be whitelisted, otherwise apt attempts
fetching target arch packages from archive and security, and they are
not there.

Another issue was with libelf-dev:s390x dependencies. Current
linux-libc-dev breaks linux-libc-dev:s390x, and unfortunately we need
both for a proper cross-compilation build. Using aptituide I found
that downgrading linux-libc-dev:amd64 resolves this conflict.

[1] actions/runner-images#10901
[2] https://discourse.ubuntu.com/t/ubuntu-24-04-lts-noble-numbat-release-notes/39890#p-99950-deb822-sources-management

Signed-off-by: Ihor Solodrai <[email protected]>

Author: theihor

setup-build-env/install_cross_compilation_toolchain.sh

@@ -4,28 +4,62 @@ set -euo pipefail
 
 THISDIR="$(cd "$(dirname "$0")" && pwd)"
 
-# shellcheck source=./helpers.sh
 source "${THISDIR}"/../helpers.sh
 
 TARGET_ARCH="$1"
 
 foldable start install_crosscompile "Installing Cross-Compilation toolchain"
 
-if [[ "${TARGET_ARCH}" != "$(uname -m)" ]]
-then
-	DEB_ARCH="$(platform_to_deb_arch "${TARGET_ARCH}")"
-	# shellcheck source=/dev/null
-	. /etc/os-release
-	cat <<EOF > /etc/apt/sources.list.d/xcompile.list
-deb [arch=${DEB_ARCH}] http://ports.ubuntu.com/ubuntu-ports  ${VERSION_CODENAME} main restricted
-deb [arch=${DEB_ARCH}] http://ports.ubuntu.com/ubuntu-ports  ${VERSION_CODENAME}-updates main restricted
-EOF
-	apt update
-	# Add the architecture
-	dpkg --add-architecture "${DEB_ARCH}"
-	apt install -y g{cc,++}-"${TARGET_ARCH}-linux-gnu" {libelf-dev,libssl-dev}:"${DEB_ARCH}"
-else
+if [[ "${TARGET_ARCH}" == "$(uname -m)" ]]; then
     echo "Nothing to do. Target arch is the same as host arch: ${TARGET_ARCH}"
+    exit 0
 fi
 
+source /etc/os-release
+
+DEB_ARCH="$(platform_to_deb_arch "${TARGET_ARCH}")"
+DEB_HOST_ARCH="$(dpkg --print-architecture)"
+UBUNTU_CODENAME=${VERSION_CODENAME:-noble}
+
+cat <<EOF | sudo tee /etc/apt/sources.list.d/ubuntu.sources
+Types:        deb
+URIs:         http://archive.ubuntu.com/ubuntu/
+Suites:       ${UBUNTU_CODENAME} ${UBUNTU_CODENAME}-updates ${UBUNTU_CODENAME}-backports
+Components:   main restricted universe multiverse
+Architectures:   ${DEB_HOST_ARCH}
+Signed-By:    /usr/share/keyrings/ubuntu-archive-keyring.gpg
+
+Types:        deb
+URIs:         http://security.ubuntu.com/ubuntu/
+Suites:       ${UBUNTU_CODENAME}-security
+Components:   main restricted universe multiverse
+Architectures:   ${DEB_HOST_ARCH}
+Signed-By:    /usr/share/keyrings/ubuntu-archive-keyring.gpg
+EOF
+
+sudo dpkg --add-architecture "$DEB_ARCH"
+cat <<EOF | sudo tee /etc/apt/sources.list.d/xcompile.sources
+Types: deb
+URIs: http://ports.ubuntu.com/ubuntu-ports
+Suites: ${UBUNTU_CODENAME} ${UBUNTU_CODENAME}-updates ${UBUNTU_CODENAME}-security
+Components: main restricted universe multiverse
+Architectures: ${DEB_ARCH}
+Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
+EOF
+
+sudo apt-get update -y
+
+# downgrade due to conflict with linux-libc-dev:s390x
+sudo apt-get install --allow-downgrades -y linux-libc-dev=6.8.0-57.59
+
+sudo apt-get install -y                  \
+     "crossbuild-essential-${DEB_ARCH}"  \
+     "binutils-${TARGET_ARCH}-linux-gnu" \
+     "gcc-${TARGET_ARCH}-linux-gnu"      \
+     "g++-${TARGET_ARCH}-linux-gnu"      \
+     "linux-libc-dev:${DEB_ARCH}"        \
+     "libelf-dev:${DEB_ARCH}"            \
+     "libssl-dev:${DEB_ARCH}"            \
+     "zlib1g-dev:${DEB_ARCH}"
+
 foldable end install_crosscompile