ui-smoke: capture a native backtrace on GUI crash

PYTHONFAULTHANDLER stops at the Python frame; a Qt/dbus/GL segfault
needs the C stack. Arm a core dump in the launchers and, if the GUI
leaves a core, gdb its backtrace into the log. Failure-path only, so
green runs pay nothing.

Author: grandixximo

tests/ui-smoke/_lib/crashdump.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+# Native crash capture for the UI smoke launchers. A GUI segfault is the
+# failure these tests most need to explain, and it lands in C/C++ (Qt,
+# dbus, GL) where PYTHONFAULTHANDLER stops at the event-loop frame. Arm a
+# core dump before launch; after the run, if the GUI left a core, print a
+# native backtrace into the log so CI shows the faulting frame directly.
+# Source with LIB_DIR set; runs only on the failure path, so green runs
+# pay nothing.
+
+crashdump_arm() {
+    CORE_DIR="$(mktemp -d -t ui-smoke-cores.XXXXXX)"
+    export CORE_DIR
+    ulimit -c unlimited 2>/dev/null || true
+    # core_pattern is global and needs root; best-effort (CI has sudo).
+    # If it does not take, crashdump_report still finds a cwd "core".
+    sudo sysctl -w "kernel.core_pattern=$CORE_DIR/core.%e.%p" >/dev/null 2>&1 || true
+}
+
+crashdump_report() {
+    [ -n "${CORE_DIR:-}" ] || return 0
+    local core
+    # shellcheck disable=SC2012  # mktemp dir, no odd filenames
+    core=$(ls -t "$CORE_DIR"/core* ./core* /tmp/core* 2>/dev/null | head -1)
+    if [ -n "$core" ]; then
+        echo "=== crash: native backtrace ($core) ==="
+        # gdb is not on the CI runner by default; pull it in to read the core.
+        command -v gdb >/dev/null 2>&1 || sudo apt-get install -y -q gdb >/dev/null 2>&1 || true
+        if command -v gdb >/dev/null 2>&1; then
+            # "bt" first: gdb auto-selects the faulting thread on a SIGSEGV
+            # core. "thread apply all bt" after gives the rest.
+            gdb -batch -nx \
+                -ex "bt" \
+                -ex "echo \n=== all threads ===\n" \
+                -ex "thread apply all bt" \
+                "$(command -v python3)" "$core" 2>&1 | head -400
+        else
+            echo "(gdb unavailable; core left at $core)"
+        fi
+    fi
+    rm -rf "$CORE_DIR"
+}

tests/ui-smoke/_lib/launch.sh

@@ -39,6 +39,10 @@ DRIVER_TIMEOUT=180
 # launch-env.sh so launch.sh and quit-launch.sh cannot drift apart.
 . "$LIB_DIR/launch-env.sh"
 
+# Arm a core dump so a GUI segfault can be backtraced after the run.
+. "$LIB_DIR/crashdump.sh"
+crashdump_arm
+
 # Export the per-invocation values so the inner bash -c receives them
 # as proper env vars (avoids embedding paths into the inner script
 # via quoting, which breaks on apostrophes / spaces).
@@ -102,4 +106,7 @@ echo "=== ui-smoke.out ==="
 echo "=== ui-smoke.err ==="
 [ -f ui-smoke.err ] && cat ui-smoke.err
 
+# If the GUI dumped a core, print its native backtrace.
+crashdump_report
+
 exit "$RC"

tests/ui-smoke/_lib/quit-launch.sh

@@ -39,6 +39,10 @@ QUIT_GRACE=15
 # launch-env.sh so launch.sh and quit-launch.sh cannot drift apart.
 . "$LIB_DIR/launch-env.sh"
 
+# Arm a core dump so a GUI segfault can be backtraced after the run.
+. "$LIB_DIR/crashdump.sh"
+crashdump_arm
+
 export CONFIG_INI LIB_DIR DRIVER_TIMEOUT GUI_MATCH QUIT_GRACE
 
 # shellcheck disable=SC2016
@@ -117,4 +121,7 @@ echo "=== linuxcnc.err ==="
 echo "=== ui-smoke.out ==="
 [ -f ui-smoke.out ] && cat ui-smoke.out
 
+# If the GUI dumped a core, print its native backtrace.
+crashdump_report
+
 exit "$RC"