ci: Improve OpenBSD core dump backtrace handling.

Since OpenBSD core dumps do not embed executable paths, the script now
searches for the corresponding binary manually within the specified
directory before invoking LLDB.  This is imperfect but should find the
right executable in practice, as needed for meaningful backtraces.

Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Discussion: https://postgr.es/m/CAN55FZ36R74TZ8RKsFueYwLxGKDAm3LU2FHM_ZUCSB6imd3vYA@mail.gmail.com
Backpatch-through: 18

.cirrus.tasks.yml

@@ -328,6 +328,7 @@ task:
         OS_NAME: openbsd
         IMAGE_FAMILY: pg-ci-openbsd-postgres
         PKGCONFIG_PATH: '/usr/lib/pkgconfig:/usr/local/lib/pkgconfig'
+        CORE_DUMP_EXECUTABLE_DIR: $CIRRUS_WORKING_DIR/build/tmp_install/usr/local/pgsql/bin
 
         MESON_FEATURES: >-
           -Dbsd_auth=enabled
@@ -396,7 +397,7 @@ task:
       # ${CORE_DUMP_DIR}, they may not obey this. So, move core files to the
       # ${CORE_DUMP_DIR} directory.
       find build/ -type f -name '*.core' -exec mv '{}' ${CORE_DUMP_DIR} \;
-      src/tools/ci/cores_backtrace.sh ${OS_NAME} ${CORE_DUMP_DIR}
+      src/tools/ci/cores_backtrace.sh ${OS_NAME} ${CORE_DUMP_DIR} ${CORE_DUMP_EXECUTABLE_DIR}
 
 
 # configure feature flags, shared between the task running the linux tests and

src/tools/ci/cores_backtrace.sh

@@ -1,12 +1,18 @@
 #! /bin/sh
 
-if [ $# -ne 2 ]; then
+os=$1
+directory=$2
+executable_directory=$3
+
+if [ "$os" != 'openbsd' ] && [ $# -ne 2 ]; then
     echo "cores_backtrace.sh <os> <directory>"
     exit 1
 fi
 
-os=$1
-directory=$2
+if [ "$os" = 'openbsd' ] && [ $# -ne 3 ]; then
+    echo "cores_backtrace.sh <os> <core_directory> <executable_directory>"
+    exit 1
+fi
 
 case $os in
     freebsd|linux|macos|netbsd|openbsd)
@@ -17,6 +23,10 @@ case $os in
     ;;
 esac
 
+if [ "$os" = 'openbsd' ]; then
+    export PATH="${executable_directory}:${PATH}"
+fi
+
 first=1
 for corefile in $(find "$directory" -type f) ; do
     if [ "$first" -eq 1 ]; then
@@ -26,8 +36,21 @@ for corefile in $(find "$directory" -type f) ; do
         echo -e '\n\n'
     fi
 
-    if [ "$os" = 'macos' ] || [ "$os" = 'openbsd' ]; then
+    if [ "$os" = 'macos' ]; then
         lldb -c $corefile --batch -o 'thread backtrace all' -o 'quit'
+    elif [ "$os" = 'openbsd' ]; then
+        # OpenBSD's ELF format doesn't include executable information, so we
+        # search for the executable manually in <executable_directory>.
+        filename=$(basename "$corefile")
+        base=$(echo "$filename" | sed 's/\.core.*$//')
+        binary=$(which "${base}")
+
+        if [ -z "$binary" ]; then
+            echo "executable ${base} not found in ${PATH}, running 'lldb' without debug information"
+            lldb -c "$corefile" --batch -o 'thread backtrace all' -o 'quit'
+        else
+            lldb "$binary" -c "$corefile" --batch -o 'thread backtrace all' -o 'quit'
+        fi
     else
         auxv=$(gdb --quiet --core ${corefile} --batch -ex 'info auxv' 2>/dev/null)
         if [ $? -ne 0 ]; then