Link to build or pfq page.
https://uberchromegw.corp.google.com/i/chromeos/builders/guado_moblab-paladin/builds/9721

build # for that buildbot.
9721

Snippet of log that contains the failure.

chromeos-bsp-moblab-0.0.1-r31:  * [new branch]            toolchainB              -> origin/toolchainB
chromeos-bsp-moblab-0.0.1-r31: GIT update -->
chromeos-bsp-moblab-0.0.1-r31:    repository:               https://chromium.googlesource.com/chromiumos/overlays/board-overlays.git
chromeos-bsp-moblab-0.0.1-r31:    at the commit:            7f4dc7ac892038caf67b4e3a325422e23994a244
chromeos-bsp-moblab-0.0.1-r31:    commit:                   dfc54e352903a0b43ae65e5224399a86b25a1b0b
chromeos-bsp-moblab-0.0.1-r31:    branch:                   master
chromeos-bsp-moblab-0.0.1-r31:    storage directory:        "/var/cache/chromeos-cache/distfiles/target/egit-src/chromiumos/overlays/board-overlays"
chromeos-bsp-moblab-0.0.1-r31:    checkout type:            bare repository
chromeos-bsp-moblab-0.0.1-r31: Cloning into '/build/guado_moblab/tmp/portage/chromeos-base/chromeos-bsp-moblab-0.0.1-r31/work/chromeos-bsp-moblab-0.0.1'...
chromeos-bsp-moblab-0.0.1-r31: done.
chromeos-bsp-moblab-0.0.1-r31: fatal: reference is not a tree: dfc54e352903a0b43ae65e5224399a86b25a1b0b
chromeos-bsp-moblab-0.0.1-r31:  * ERROR: chromeos-base/chromeos-bsp-moblab-0.0.1-r31::moblab failed (unpack phase):
chromeos-bsp-moblab-0.0.1-r31:  *   git-2_branch: changing the branch failed
chromeos-bsp-moblab-0.0.1-r31:  * 
chromeos-bsp-moblab-0.0.1-r31:  * Call stack:
chromeos-bsp-moblab-0.0.1-r31:  *     ebuild.sh, line  133:  Called src_unpack
chromeos-bsp-moblab-0.0.1-r31:  *   environment, line 3967:  Called cros-workon_src_unpack
chromeos-bsp-moblab-0.0.1-r31:  *   environment, line 1118:  Called git-2_src_unpack
chromeos-bsp-moblab-0.0.1-r31:  *   environment, line 2893:  Called git-2_branch
chromeos-bsp-moblab-0.0.1-r31:  *   environment, line 2673:  Called die
chromeos-bsp-moblab-0.0.1-r31:  * The specific snippet of code:
chromeos-bsp-moblab-0.0.1-r31:  *       git checkout -b ${branchname} ${src} || die "${FUNCNAME}: changing the branch failed";
chromeos-bsp-moblab-0.0.1-r31:  * 
chromeos-bsp-moblab-0.0.1-r31:  * If you need support, post the output of `emerge --info '=chromeos-base/chromeos-bsp-moblab-0.0.1-r31::moblab'`,
chromeos-bsp-moblab-0.0.1-r31:  * the complete build log and the output of `emerge -pqv '=chromeos-base/chromeos-bsp-moblab-0.0.1-r31::moblab'`.
chromeos-bsp-moblab-0.0.1-r31:  * The complete build log is located at '/build/guado_moblab/tmp/portage/logs/chromeos-base:chromeos-bsp-moblab-0.0.1-r31:20180620-040931.log'.
chromeos-bsp-moblab-0.0.1-r31:  * For convenience, a symlink to the build log is located at '/build/guado_moblab/tmp/portage/chromeos-base/chromeos-bsp-moblab-0.0.1-r31/temp/build.log'.
chromeos-bsp-moblab-0.0.1-r31:  * The ebuild environment file is located at '/build/guado_moblab/tmp/portage/chromeos-base/chromeos-bsp-moblab-0.0.1-r31/temp/environment'.
chromeos-bsp-moblab-0.0.1-r31:  * Working directory: '/build/guado_moblab/tmp/portage/chromeos-base/chromeos-bsp-moblab-0.0.1-r31/work/chromeos-bsp-moblab-0.0.1'
chromeos-bsp-moblab-0.0.1-r31:  * S: '/build/guado_moblab/tmp/portage/chromeos-base/chromeos-bsp-moblab-0.0.1-r31/work/chromeos-bsp-moblab-0.0.1'
chromeos-bsp-moblab-0.0.1-r31: >>> Failed to emerge chromeos-base/chromeos-bsp-moblab-0.0.1-r31 for /build/guado_moblab/, Log file:
chromeos-bsp-moblab-0.0.1-r31: >>>  '/build/guado_moblab/tmp/portage/logs/chromeos-base:chromeos-bsp-moblab-0.0.1-r31:20180620-040931.log'
chromeos-bsp-moblab-0.0.1-r31: 
chromeos-bsp-moblab-0.0.1-r31:  * Messages for package chromeos-base/chromeos-bsp-moblab-0.0.1-r31 merged to /build/guado_moblab/:
chromeos-bsp-moblab-0.0.1-r31: 
chromeos-bsp-moblab-0.0.1-r31:  * Cannot run git checkout dfc54e352903a0b43ae65e5224399a86b25a1b0b in /build/guado_moblab/tmp/portage/chromeos-base/chromeos-bsp-moblab-0.0.1-r31/work/chromeos-bsp-moblab-0.0.1.
chromeos-bsp-moblab-0.0.1-r31:  * Is /mnt/host/source/src/platform/../overlays/ up to date? Try running repo sync.
chromeos-bsp-moblab-0.0.1-r31:  * Falling back to git.eclass...
chromeos-bsp-moblab-0.0.1-r31:  * ERROR: chromeos-base/chromeos-bsp-moblab-0.0.1-r31::moblab failed (unpack phase):
chromeos-bsp-moblab-0.0.1-r31:  *   git-2_branch: changing the branch failed
chromeos-bsp-moblab-0.0.1-r31:  * 
chromeos-bsp-moblab-0.0.1-r31:  * Call stack:
chromeos-bsp-moblab-0.0.1-r31:  *     ebuild.sh, line  133:  Called src_unpack
chromeos-bsp-moblab-0.0.1-r31:  *   environment, line 3967:  Called cros-workon_src_unpack
chromeos-bsp-moblab-0.0.1-r31:  *   environment, line 1118:  Called git-2_src_unpack
chromeos-bsp-moblab-0.0.1-r31:  *   environment, line 2893:  Called git-2_branch
chromeos-bsp-moblab-0.0.1-r31:  *   environment, line 2673:  Called die
chromeos-bsp-moblab-0.0.1-r31:  * The specific snippet of code:
chromeos-bsp-moblab-0.0.1-r31:  *       git checkout -b ${branchname} ${src} || die "${FUNCNAME}: changing the branch failed";
chromeos-bsp-moblab-0.0.1-r31:  * 
chromeos-bsp-moblab-0.0.1-r31:  * If you need support, post the output of `emerge --info '=chromeos-base/chromeos-bsp-moblab-0.0.1-r31::moblab'`,
chromeos-bsp-moblab-0.0.1-r31:  * the complete build log and the output of `emerge -pqv '=chromeos-base/chromeos-bsp-moblab-0.0.1-r31::moblab'`.
chromeos-bsp-moblab-0.0.1-r31:  * The complete build log is located at '/build/guado_moblab/tmp/portage/logs/chromeos-base:chromeos-bsp-moblab-0.0.1-r31:20180620-040931.log'.
chromeos-bsp-moblab-0.0.1-r31:  * For convenience, a symlink to the build log is located at '/build/guado_moblab/tmp/portage/chromeos-base/chromeos-bsp-moblab-0.0.1-r31/temp/build.log'.
chromeos-bsp-moblab-0.0.1-r31:  * The ebuild environment file is located at '/build/guado_moblab/tmp/portage/chromeos-base/chromeos-bsp-moblab-0.0.1-r31/temp/environment'.
chromeos-bsp-moblab-0.0.1-r31:  * Working directory: '/build/guado_moblab/tmp/portage/chromeos-base/chromeos-bsp-moblab-0.0.1-r31/work/chromeos-bsp-moblab-0.0.1'
chromeos-bsp-moblab-0.0.1-r31:  * S: '/build/guado_moblab/tmp/portage/chromeos-base/chromeos-bsp-moblab-0.0.1-r31/work/chromeos-bsp-moblab-0.0.1'
=== Complete: job chromeos-bsp-moblab-0.0.1-r31 (0m2.0s) ===
Failed chromeos-base/chromeos-bsp-moblab-0.0.1-r31 (in 0m2.0s). Your build has failed.
Pending 2/644, [Time 21:09:33 | Elapsed 61m46.0s | Load 3.72 8.95 28.7]
Packages failed:
	chromeos-base/chromeos-bsp-moblab-0.0.1-r31