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Fastboot

This documentation presents the particularities of the Kernelflinger Fastboot implementation. For fastboot standard commands, please refer to fastboot --help.

Non-standard flash commands

flash gpt <filename>

Unlocked devices only. Provisions the GPT partition scheme on the device, accepting an gpt.bin file which contains a specification for the device's GPT.

Two gpt.bin formats are accepted:

1. gpt_ini2bin.py

gpt.bin file is generated using the gpt_ini2bin.py script from a gpt.ini file.

Here is a gpt.ini file example:

[base]
partitions = bootloader bootloader2 boot recovery misc metadata system cache data persistent
device = auto

[partition.bootloader]
label = bootloader
len = 60
type = esp

[partition.bootloader2]
label = bootloader2
len = 60
type = fat

[partition.boot]
label = boot
len = 30
type = boot

[partition.recovery]
label = recovery
len = 30
type = recovery

[partition.misc]
label = misc
len = 1
type = misc

[partition.metadata]
label = metadata
len = 16
type = metadata

[partition.system]
label = system
len = 2560
type = linux

[partition.cache]
label = cache
len = 100
type = linux

[partition.data]
label = data
len = -1
type = linux

[partition.persistent]
label = persistent
len = 1
type = linux

If the Android build is using slot AB mechanism, the slot number is defined in the [base] section and every partition that have several slots have the has_slot = true parameter:

[base]
partitions = bootloader bootloader2 boot misc metadata system cache data persistent
nb_slot = 2

[...]

[partition.boot]
label = boot
len = 30
type = boot
has_slot = true

[...]

[partition.system]
label = system
len = 1024
type = linux
has_slot = true

[...]

2. bpttool

bpttool is an AOSP project that can be used to create the partition table.

fastboot flash bootloader <filename>

Unlocked devices only. Kernelfinger Fastboot implementation requires two bootloader partitions labelled bootloader and bootloader2. The flash bootloader process is the following:

  1. Flash FILENAME into the bootloader2 partition.
  2. Verify the content of the bootloader2 partition:
  • bootloader2 contains a FAT16 or FAT32 file-system
  • the usual bootloader EFI binary is present and loadable
  • and all the EFI binaries described in the /manifest.txt file are present and loadable.
  1. Switch the bootloader and bootloader2 entries in the GPT header.
  2. Create the load options based on the bootloader partition /manifest.txt file.

Here is an example of a /manifest.txt file:

Android-IA=/EFI/BOOT/bootx64.efi
Fastboot=/EFI/BOOT/bootx64.efi;-f

This /manifest.txt file makes Kernelflinger create two load options Android-IA and Fastboot. The Fastboot load option makes the EFI Boot Manager start Kernelflinger with the "-f" supplied argument, enforcing Kernelflinger to start in Fastboot mode.

fastboot flash oemvars <filename>

Unlocked devices only. OEM variables are stored as EFI variables. By default, they are under the Loader GUID of 4a67b082-0a4c-41cf-b6c7-440b29bb8c4f.

This flash command accepts a text file with a set of OEM variables to set. The syntax supports #-style end of line comments. Variable settings are specified as <var> <val>. White space around the variable name is removed, as is trailing white space at the end of the line. The value can otherwise contain any printable character and is stored as an 8-bit string in the EFI variable's value. Non-printable bytes can be encoded with %xx URL-style notation. If <val> is omitted, the variable is cleared instead.

A line of the form follows:

GUID = xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

This line changes the GUID used for subsequent lines.

Example file:

##########################
# Maximum timeout to check for magic key at boot; fastboot GUID

MagicKeyTimeout     40

##########################
# atomisp camera variables

GUID = ecb54cd9-e5ae-4fdc-a971-e877756068f7

# ECS boards use this GPIO line to gate 2.8v camera power
gmin_V2P8GPIO 402

# OV5693 world-facing camera
INT33BE:00_CsiPort   1
INT33BE:00_CsiLanes  2
INT33BE:00_CamClk    0
INT33BE:00_CsiFmt   13
INT33BE:00_CsiBayer  2

# Aptina MT9M114 ("SOC-1040") user-facing camera
INT33F0:00_CsiPort   0
INT33F0:00_CsiLanes  1
INT33F0:00_CamClk    1
INT33F0:00_CsiFmt   13
INT33F0:00_CsiBayer  0

# Invert Audio Jack
byt_rt5640_JackInvert 1

Additionally, lines may be prefixed with modifier codes in brackets to control the flags used when setting EFI variables. By default, all values are assumed to be 8-bit NUL-terminated strings with both boot and runtime services access. Supported modifier codes are:

  • d: Raw data, do not NUL terminate
  • b: Restrict to boot services access
  • a: Time-based authenticated variable

For example:

[db] MyBinaryVar %ab%cd%ef

This example sets MyBinaryVar to the hex values 0xAB 0xCD 0xEF with no terminating NUL byte and boot services access only.

flash /ESP/<dest-path> <filename>

Unlocked devices only. Copy FILENAME into the EFI system partition. Any directory included in DEST path will also be created.

OEM commmands

oem setvar <var-name> [<var-value>]

Unlocked devices only. Sets an EFI variable under the Loader GUID 4a67b082-0a4c-41cf-b6c7-440b29bb8c4f with the specified key, to the value provided. The value is always stored as an 8-bit NUL-terminated string. Omitting the value will result in the variable being set to NUL which will erase the variable.

Some interesting values that can be set are:

  • SerialPort: Value is appended to console= in the kernel command line for setting the device's console port.
  • AppendCmdline, PrependCmdline, and ReplaceCmdline:
  1. The content of variable PrependCmdline will be prepended to the original commandline.
  2. The content of variable AppendCmdline will be appended to the original commandline.
  3. The content of variable ReplaceCmdline will replace the whole original commandline.
  4. The PrependCmdline and AppendCmdline will still be effective, using the content of RepaceCmdline.
  5. AppendCmdline, PrependCmdline, and ReplaceCmdline will be ignored in a user build.

Other values are inherently device-specific. Normally this command is only of interest to developers. Factory provisioning uses flash oemvars instead.

oem garbage-disk

Unlocked devices only. Writes out the entire disk with random data, including the partition table. Used in device provisioning test cases to ensure that the previous device state does not influence the outcome of the tests applied.

oem reboot <target>

Works in any device state. Reboots the device into the specified boot TARGET. Functionally equivalent to adb reboot <target>.

oem reprovision

Works in any device state. This is only available in eng or userdebug builds. It puts the device back into provisioning mode, which allows several things:

  • The device may be unlocked without enforcing Factory Reset Protection. The state of the persistent partition doesn't matter.
  • Transitions between {locked|unlocked} states do not require user confirmation or erasing of the userdata partition.

Provisioning mode is also the state the device is in when it is freshly manufactured. The device leaves provisioning mode once you run any of the flashing {lock|unlock} commands and you reset the device.

oem rm /ESP/<filename>

Unlocked devices only. Erase FILENAME from the EFI system partition.

oem get-hashes <hash-algorithm>

Works in any device state. This is used by OTA Secure Boot Test Cases to verify the correctness of device provisioning and OTA updates. Various boot images, the contents of the EFI system partition, and the block-level /system and /vendor images (including verity tables and metadata) are HASH-ALGORITHM hashed and reported back to the user.

Example:

...
& fastboot oem get-hashes
(bootloader) target: /boot
(bootloader) hash: d0448a1e91030e5c37277e4a77eabefc36fc8e6c
(bootloader) target: /recovery
(bootloader) hash: 411c61de23f6f73934b79eda4f64779706c220f4
(bootloader) target: /bootloader/EFI/BOOT/bootx64.efi
(bootloader) hash: 2773c4c039dc37b96171f6ef131f04dd8faf73e1
(bootloader) target: /bootloader/loader.efi
(bootloader) hash: 2773c4c039dc37b96171f6ef131f04dd8faf73e1
(bootloader) target: /bootloader/fastboot.img
(bootloader) hash: b0b3d122c4dca255ed2a75268ef30f6cbbc11085
(bootloader) target: /system
(bootloader) hash: d417239a25df718d73b6326e6c93a7fc1b00afb2
OKAY [134.307s]
finished. total time: 134.307s

This command takes an optional argument to specify which HASH-ALGORITHM must be used. Accepted values are "sha1" and "md5". The default behaviour (no argument supplied) is "sha1". Note that "md5" is by far faster than "sha1".

oem get-provisioning-logs

Works in any state. Displays the contents of the KernelflingerLogs EFI variable. Useful if Kernelflinger crashes or hits an error at manufacturing where no debug board or screen is connected.

oem set-storage <storage>

Works in any state but is limited to non-user builds. For devices with both EMMC and UFS, this command is used to enforce one or the other. STORAGE value is limited to emmc and ufs.

fastboot oem crash-event-menu <0|1>

Enable (1) or disable(0) Crashmode.

fastboot oem slot-fallback <0|1>

Works in any state but is limited to non-user builds. Enable (1) or disable(0) slot fallback mechanism. If set to 0, the active slot and the recovery remaining tries number are not decremented.

oem set-watchdog-counter-max <value>

Works in any device state but is limited to non-user builds.

This command sets the maximum number of crash events in a row before Crashmode is displayed. VALUE is comprised between 0 included and 255 included.

oem get-action-nonce <action>

Works in any device state. See. Bootloader policy and Factory Reset Protection.

oem erase-efivars

Works in any device state but is limited to non-user builds. This commands deletes all the EFI variables declared under the Loader GUID or Fastboot GUID except:

  • The "OEMLock" EFI variable declared under the Fastboot GUID
  • The "KernelflingerLogs" EFI variable declared under the Loader GUID
  • All the "Bootloader policy" time-based authenticated EFI variables declared under the Fastboot GUID. See. Bootloader policy and Factory Reset Protection.

Non-standard Variables

secureboot

Indicates whether UEFI Secure Boot is enabled. This is a pre-requisite for Verified Boot.

product-name

Reports the product_name field in DMI.

firmware

Reports the current device firmware version from DMI. Combines the values of the DMI bios_vendor and bios_version fields.

boot-state

Indicates the device's color-coded boot state as per Google verified boot's specification. If the bootloader doesn't support Verified Boot, unknown will be returned.

device-state

Indicates the device's lock state as per Google verified boot's specification.

board

Indicates the board information, combining the values of the DMI board_vendor, board_name, and board_version fields.