Configure the serial port for debugging

Enable the serial port from the build_image command line.
Currenly, you have to edit build_kernel_image.sh to enable
the serial port for kernel debugging. Now:

./build_image --board=${BOARD} --enable_serial=ttyS0

Will enable sending printks to the specified serial port.

BUG=chromium-os:38026
TEST=built images with and without serial enabled

Change-Id: I9ef4f2a20f0d451e132371339c4eba1faf4c94de
Reviewed-on: https://gerrit.chromium.org/gerrit/41638
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Paul Taysom <taysom@chromium.org>
Tested-by: Paul Taysom <taysom@chromium.org>

bin/cros_make_image_bootable

@@ -145,6 +145,9 @@ DEFINE_boolean enable_squashfs ${FLAGS_FALSE} \
 DEFINE_string squash_sort_file "" \
   "Specify the priority of files when squashing the rootfs."
 
+DEFINE_string enable_serial "" \
+  "Enable serial port for printks. Example values: ttyS0"
+
 # Parse the boot.desc and any overrides
 eval set -- "${BOOT_DESC} ${FLAG_OVERRIDES}"
 FLAGS "${@}" || exit 1
@@ -240,6 +243,7 @@ make_image_bootable() {
     --verity_error_behavior=${FLAGS_verity_error_behavior} \
     --verity_salt=${FLAGS_verity_salt} \
     --keys_dir="${FLAGS_keys_dir}" \
+    --enable_serial="${FLAGS_enable_serial}" \
     ${enable_rootfs_verification_flag} \
     ${enable_bootcache_flag} \
     ${use_dev_keys}

build_image

@@ -31,6 +31,8 @@ DEFINE_boolean standard_backdoor ${FLAGS_TRUE} \
   "Install standard backdoor credentials for testing"
 DEFINE_string usb_disk /dev/sdb3 \
   "Path syslinux should use to do a usb boot. Default: /dev/sdb3"
+DEFINE_string enable_serial "" \
+  "Enable serial port for printks. Example values: ttyS0"
 
 FLAGS_HELP="USAGE: build_image [flags] [list of images to build].
 This script is used to build a Chromium OS image. Chromium OS comes in many

build_kernel_image.sh

@@ -49,6 +49,8 @@ DEFINE_boolean enable_rootfs_verification ${FLAGS_TRUE} \
   "Enable kernel-based root fs integrity checking. (Default: true)"
 DEFINE_boolean enable_bootcache ${FLAGS_FALSE} \
   "Enable boot cache to accelerate booting. (Default: false)"
+DEFINE_string enable_serial "" \
+  "Enable serial port for printks. Example values: ttyS0"
 
 # Parse flags
 FLAGS "$@" || exit 1
@@ -180,10 +182,25 @@ WORK="${WORK} ${FLAGS_working_dir}/boot.config"
 info "Emitted cross-platform boot params to ${FLAGS_working_dir}/boot.config"
 
 # Add common boot options first.
-cat <<EOF | cat - "${FLAGS_working_dir}/boot.config" \
-  > "${FLAGS_working_dir}/config.txt"
-loglevel=7
+config="${FLAGS_working_dir}/config.txt"
+if [[ -n ${FLAGS_enable_serial} ]]; then
+  console=${FLAGS_enable_serial}
+  if [[ ${console} != *,* ]]; then
+    console+=",115200n8"
+  fi
+  cat <<EOF > "${config}"
+console=${console}
+earlyprintk=${console}
+console=tty1
+EOF
+else
+  cat <<EOF > "${config}"
 console=
+EOF
+fi
+
+cat <<EOF - "${FLAGS_working_dir}/boot.config" >> "${config}"
+loglevel=7
 init=/sbin/init
 cros_secure
 EOF

build_library/build_image_util.sh

@@ -139,6 +139,7 @@ create_boot_desc() {
   --boot_args="${FLAGS_boot_args}"
   --nocleanup_dirs
   --verity_algorithm=sha1
+  --enable_serial="${FLAGS_enable_serial}"
   ${enable_rootfs_verification_flag}
   ${enable_bootcache_flag}
 EOF