Makefile: add kernel debugging flags for qemu

Author: stapelberg

Diff for: Makefile

@@ -30,6 +30,28 @@ QEMU=qemu-system-x86_64 \
 	-device virtio-scsi-pci,id=scsi \
 	-device scsi-hd,drive=hd
 
+# To use gdb to debug the Linux kernel, use e.g.:
+#
+# make qemu-serial \
+#   kgdb=1 \
+#   kernel=/home/michael/fuse-debug/linux/arch/x86/boot/bzImage \
+#   cmdline="panic_on_oops=1"
+#
+# gdb vmlinux
+# (gdb) target remote localhost:1234
+# (gdb) continue
+ifdef kgdb
+cmdline+= nokaslr
+cmdline+= kgdbwait
+cmdline+= kgdboc=ttyS0,115200
+QEMU+= -serial tcp::1234,server,nowait
+endif
+
+ifdef kernel
+QEMU+= -kernel "${kernel}"
+QEMU+= -append "root=/dev/sda4 ro ${cmdline} $(shell tr -d '\n' < ${DISKIMG}.cmdline)"
+endif
+
 PACKFLAGS=
 
 # for when you want to see non-kernel console output (e.g. systemd), useful with qemu

Diff for: cmd/distri/pack.go

@@ -861,7 +861,11 @@ name=root`)
 	if p.bootDebug {
 		params = append(params, "systemd.log_level=debug systemd.log_target=console")
 	}
-	mkconfigCmd := "GRUB_CMDLINE_LINUX=\"console=ttyS0,115200 " + strings.Join(params, " ") + " init=/init systemd.setenv=PATH=/bin rw\" GRUB_TERMINAL=serial grub-mkconfig -o /boot/grub/grub.cfg"
+	cmdline := "console=ttyS0,115200 " + strings.Join(params, " ") + " init=/init systemd.setenv=PATH=/bin rw"
+	if err := ioutil.WriteFile(p.diskImg+".cmdline", []byte(cmdline+"\n"), 0644); err != nil {
+		return err
+	}
+	mkconfigCmd := fmt.Sprintf(`GRUB_CMDLINE_LINUX=%q GRUB_TERMINAL=serial grub-mkconfig -o /boot/grub/grub.cfg`, cmdline)
 	mkconfig := exec.Command("sudo", "chroot", "/mnt", "sh", "-c", mkconfigCmd)
 	mkconfig.Stderr = os.Stderr
 	mkconfig.Stdout = os.Stdout