Add a post-link script for Linux which fixes up rpath

- script is clean according to shellcheck.net
- added the script to the QGCPostLinkCommon
- added patchelf to the Dockerfile and the github workflows for Linux

.github/workflows/linux_debug.yml

@@ -45,6 +45,9 @@ jobs:
       - name: Install ccache
         run:  sudo apt-get install ccache
 
+      - name: Install post-link dependencies
+        run:  sudo apt-get install -y patchelf
+
       - name: Prepare ccache timestamp
         id: ccache_cache_timestamp
         shell: cmake -P {0}

.github/workflows/linux_release.yml

@@ -46,6 +46,9 @@ jobs:
       - name: Install ccache
         run:  sudo apt-get install ccache
 
+      - name: Install post-link dependencies
+        run:  sudo apt-get install -y patchelf
+
       - name: Prepare ccache timestamp
         id: ccache_cache_timestamp
         shell: cmake -P {0}

QGCPostLinkCommon.pri

@@ -163,4 +163,6 @@ LinuxBuild {
     } else {
         include($$PWD/custom/custom_deploy.pri)
     }
+
+    QMAKE_POST_LINK += && QTDIR="$$DESTDIR/Qt" RPATHDIR="$$DESTDIR/Qt/libs" QTCONF_PATH="$$DESTDIR/qt.conf" $$SOURCE_DIR/deploy/linux-post-link.sh
 }

deploy/docker/Dockerfile-build-linux

@@ -47,6 +47,7 @@ RUN apt update && apt -y --quiet --no-install-recommends install \
 		ninja-build \
 		openssh-client \
 		openssl \
+		patchelf \
 		pkg-config \
 		rsync \
 		speech-dispatcher \

deploy/linux-post-link.sh

@@ -0,0 +1,72 @@
+#!/usr/bin/bash
+#
+# Premise:
+# Shared libraries (Qt, airmap, etc) on Linux are built without knowing where
+# they will be installed to; they assume they will be installed to the system.
+#
+# QGC does not install to the system. Instead it copies them to `Qt/libs`. The
+# libraries need to have their rpath set correctly to ensure that the built
+# application and its libraries are found at runtime. Without this step then the
+# libraries won't be found. You might not notice it if you have the libraries
+# installed in your system. A lot of systems will have the Qt libs installed,
+# but they might be a different version. It "might" work, it might cause subtle
+# bugs, or it might not work at all.
+#
+# To patch the libraries, a tool called `patchelf` is used.
+#
+# If the libraries' rpath isn't set correctly then LD_LIBRARY_PATH would need
+# to be used, like such:
+# LD_LIBRARY_PATH=./Qt/libs ./QGroundControl
+#
+# In addition, Qt will sometimes want to reference its own directory to find
+# certain resources. This installs a file, qt.conf, which tells Qt where its
+# installation is at.
+# Without the qt.conf file, you would need to tell Qt where to find certain
+# files, particularly for QML, like such:
+# QML2_IMPORT_PATH=./Qt/qml QT_PLUGIN_PATH=./Qt/plugins ./QGroundControl
+#
+
+# -x: echo
+# -e: stop on error
+# -u: undefined variable use is an error
+# -o pipefail: if any part of a pipeline fails, then the whole pipeline fails.
+set -xeuo pipefail
+
+# To set these arguments, set them as an environment variable. For example:
+# QTDIR=/opt/qgc-deploy/Qt RPATHDIR=/opt/qgc-deploy/Qt/libs QTCONF_PATH=/opt/qgc-deploy/qt.conf ./linux-post-link.sh
+: "${QTDIR:=./Qt}"
+: "${RPATHDIR:="${QTDIR}/libs"}"
+: "${QTCONF_PATH:=./qt.conf}"
+
+# find:
+#    type f (files)
+#    that end with '.so'
+#    or that end with '.so.5'
+#    and are executable
+#    silence stderr (find will complain if it doesn't have permission to traverse)
+find "${QTDIR}" \
+    -type f \
+    -iname '*.so' \
+    -o -iname '*.so.5' \
+    -executable \
+    2>/dev/null |
+while IFS='' read -r library; do
+    # Get the directory containing the library
+    library_dir="$(dirname "${library}")"
+
+    # Get the relative path from the library's directory to the Qt/libs directory.
+    library_rpath="$(realpath --relative-to "${library_dir}" "${RPATHDIR}")"
+
+    # patch the library's rpath to point to the Qt/libs directory.
+    # Note: '$ORIGIN' must not be expanded by the shell!
+    # shellcheck disable=SC2016
+    patchelf --set-rpath '$ORIGIN/'"${library_rpath}" "${library}"
+done
+
+# Create a qt.conf file
+# https://doc.qt.io/qt-5/qt-conf.html
+cat <<EOF > "${QTCONF_PATH}"
+[Paths]
+Prefix=./Qt
+Libraries=libs
+EOF

deploy/qgroundcontrol-start.sh

@@ -1,10 +1,7 @@
 #!/bin/sh
 HERE="$(dirname "$(readlink -f "${0}")")"
-export LD_LIBRARY_PATH="${HERE}/usr/lib/x86_64-linux-gnu":"${HERE}/Qt/libs":$LD_LIBRARY_PATH
-export QML2_IMPORT_PATH="${HERE}/Qt/qml"
-export QT_PLUGIN_PATH="${HERE}/Qt/plugins"
 
 # hack until icon issue with AppImage is resolved
-mkdir -p ~/.icons && cp ${HERE}/qgroundcontrol.png ~/.icons
+mkdir -p ~/.icons && cp "${HERE}/qgroundcontrol.png" ~/.icons
 
 "${HERE}/QGroundControl" "$@"