changed config and added info for gdb debugging

.config

@@ -203,7 +203,7 @@ CONFIG_SYSFS_SYSCALL=y
 # CONFIG_SYSCTL_SYSCALL is not set
 CONFIG_POSIX_TIMERS=y
 CONFIG_KALLSYMS=y
-# CONFIG_KALLSYMS_ALL is not set
+CONFIG_KALLSYMS_ALL=y
 CONFIG_KALLSYMS_ABSOLUTE_PERCPU=y
 CONFIG_KALLSYMS_BASE_RELATIVE=y
 CONFIG_PRINTK=y
@@ -3770,7 +3770,11 @@ CONFIG_MESSAGE_LOGLEVEL_DEFAULT=4
 #
 # Compile-time checks and compiler options
 #
-# CONFIG_DEBUG_INFO is not set
+CONFIG_DEBUG_INFO=y
+# CONFIG_DEBUG_INFO_REDUCED is not set
+# CONFIG_DEBUG_INFO_SPLIT is not set
+# CONFIG_DEBUG_INFO_DWARF4 is not set
+CONFIG_GDB_SCRIPTS=y
 # CONFIG_ENABLE_WARN_DEPRECATED is not set
 CONFIG_ENABLE_MUST_CHECK=y
 CONFIG_FRAME_WARN=2048

build

 worker=8
 
-make -j"$worker" bzImage
+time make -j"$worker" bzImage
+ln -sf scripts/gdb/vmlinux-gdb.py vmlinux-gdb.py  # fix symlink for gdb

pb_utils/readme.md

@@ -22,3 +22,20 @@ cd /mnt
 
 # run the build kernel with the created rootfs
 run `./run_qemu.sh`
+
+# debug using gdb
+run `./run_qemu.sh gdb`
+
+run in a seperate shell:
+```bash
+cd .. # to workspace root
+
+gdb vmlinux \
+    -ex 'lx-symbols' \
+    -ex 'target remote :1234' \
+    -ex 'hb init_pb_rq'
+```
+
+look for gdb `add-auto-load-safe-path` warning and follow instruction to enable loading of kernel gdb scripts
+
+use hardware breakpoints instead of software breaks

pb_utils/run_qemu.sh

@@ -9,7 +9,7 @@ COMMAND="qemu-system-x86_64"
 [ "$MODE" == "gdb" ] &&  COMMAND+=$DEBUG_OPTIONS
 COMMAND+=" -kernel $KERNEL -cpu host"
 COMMAND+=$IMAGE_OPTIONS
-COMMAND+=" -append \"root=/dev/sda rootwait rw single console=ttyS0\""
+COMMAND+=" -append \"root=/dev/sda rootwait rw single console=ttyS0 nokaslr\"" # disable kaslr for better gdb debugging
 COMMAND+=" --enable-kvm"
 COMMAND+=" --nographic"
 COMMAND+=" --smp 1"