[One (M8) Q&A, Help & Troubleshooting] sudhanshu_shah:
C:\adb>adb devices

List of devices attached

HTxxxxxxxxx device

C:\adb>adb reboot bootloader

C:\adb>fastboot reboot-bootloader

rebooting into bootloader...

OKAY [ 0.016s]

finished. total time: 0.016s

C:\adb>fastboot oem rebootRUU

...

(bootloader) Start Verify: 0

OKAY [ 0.023s]

finished. total time: 0.024s

C:\adb>fastboot flash zip C:\adb\firmware.zip

target reported max download size of 1826418688 bytes

sending 'zip' (37650 KB)...

OKAY [ 2.374s]

writing 'zip'...

(bootloader) zip header checking...

(bootloader) zip info parsing...

(bootloader) checking model ID...

(bootloader) checking custom ID...

(bootloader) start image[hboot] unzipping for pre-update check...

(bootloader) total_image_number=8

(bootloader) start image[hboot] flushing...

(bootloader) [RUU]WP,hboot,0

(bootloader) [RUU]WP,hboot,99

(bootloader) [RUU]WP,hboot,100

(bootloader) ...... Successful

(bootloader) current_image_number=0

(bootloader) start image[sbl1] unzipping for pre-update...

(bootloader) start image[sbl1] flushing...

(bootloader) signature checking...

(bootloader) verified fail

(bootloader) ...... Bypassed

(bootloader) start image[sbl1] unzipping for pre-update...

(bootloader) start image[sbl1] flushing...

(bootloader) signature checking...

(bootloader) [RUU]WP,sbl1,0

(bootloader) [RUU]WP,sbl1,100

(bootloader) ...... Successful

(bootloader) start image[sbl1] unzipping for pre-update...

(bootloader) start image[sbl1] flushing...

(bootloader) signature checking...

(bootloader) verified fail

(bootloader) ...... Bypassed

(bootloader) current_image_number=1

(bootloader) current_image_number=2

(bootloader) current_image_number=3

(bootloader) start image[rpm] unzipping for pre-update...

(bootloader) start image[rpm] flushing...

(bootloader) [RUU]WP,rpm,0

(bootloader) [RUU]WP,rpm,100

(bootloader) ...... Successful

(bootloader) current_image_number=4

(bootloader) start image[tz] unzipping for pre-update...

(bootloader) start image[tz] flushing...

(bootloader) [RUU]WP,tz,0

(bootloader) [RUU]WP,tz,100

(bootloader) ...... Successful

(bootloader) current_image_number=5

(bootloader) current_image_number=6

(bootloader) current_image_number=7

FAILED (remote: 90 hboot pre-update! please flush image again immediately)

finished. total time: 5.419s

C:\adb>fastboot flash zip C:\adb\firmware.zip

target reported max download size of 1826418688 bytes

sending 'zip' (37650 KB)...

OKAY [ 2.362s]

writing 'zip'...

(bootloader) zip header checking...

(bootloader) zip info parsing...

(bootloader) checking model ID...

(bootloader) checking custom ID...

(bootloader) total_image_number=6

(bootloader) start image[adsp] unzipping & flushing...

(bootloader) [RUU]UZ,adsp,0

(bootloader) [RUU]UZ,adsp,11

(bootloader) [RUU]UZ,adsp,22

(bootloader) [RUU]UZ,adsp,32

(bootloader) [RUU]UZ,adsp,43

(bootloader) [RUU]UZ,adsp,54

(bootloader) [RUU]UZ,adsp,65

(bootloader) [RUU]UZ,adsp,76

(bootloader) [RUU]UZ,adsp,87

(bootloader) [RUU]UZ,adsp,98

(bootloader) [RUU]UZ,adsp,100

(bootloader) [RUU]WP,adsp,0

(bootloader) [RUU]WP,adsp,100

(bootloader) ...... Successful

(bootloader) current_image_number=0

(bootloader) start image[boot] unzipping & flushing...

(bootloader) [RUU]UZ,boot,0

(bootloader) [RUU]UZ,boot,9

(bootloader) [RUU]UZ,boot,16

(bootloader) [RUU]UZ,boot,24

(bootloader) [RUU]UZ,boot,35

(bootloader) [RUU]UZ,boot,40

(bootloader) [RUU]UZ,boot,47

(bootloader) [RUU]UZ,boot,55

(bootloader) [RUU]UZ,boot,60

(bootloader) [RUU]UZ,boot,67

(bootloader) [RUU]UZ,boot,72

(bootloader) [RUU]UZ,boot,79

(bootloader) [RUU]UZ,boot,87

(bootloader) [RUU]UZ,boot,95

(bootloader) [RUU]UZ,boot,100

(bootloader) [RUU]WP,boot,0

(bootloader) [RUU]WP,boot,99

(bootloader) [RUU]WP,boot,100

(bootloader) ...... Successful

(bootloader) current_image_number=1

(bootloader) start image[sp1] unzipping & flushing...

(bootloader) [RUU]UZ,sp1,0

(bootloader) [RUU]UZ,sp1,26

(bootloader) [RUU]UZ,sp1,51

(bootloader) [RUU]UZ,sp1,75

(bootloader) [RUU]UZ,sp1,100

(bootloader) [RUU]WP,sp1,0

(bootloader) [RUU]WP,sp1,100

(bootloader) ...... Successful

(bootloader) current_image_number=2

(bootloader) start image[wcnss] unzipping & flushing...

(bootloader) [RUU]UZ,wcnss,0

(bootloader) [RUU]UZ,wcnss,23

(bootloader) [RUU]UZ,wcnss,45

(bootloader) [RUU]UZ,wcnss,68

(bootloader) [RUU]UZ,wcnss,91

(bootloader) [RUU]UZ,wcnss,100

(bootloader) [RUU]WP,wcnss,0

(bootloader) [RUU]WP,wcnss,100

(bootloader) ...... Successful

(bootloader) current_image_number=3

(bootloader) start image[radio] unzipping & flushing...

(bootloader) [RUU]UZ,radio,0

(bootloader) [RUU]UZ,radio,9

(bootloader) [RUU]UZ,radio,18

(bootloader) [RUU]UZ,radio,27

(bootloader) [RUU]UZ,radio,32

(bootloader) [RUU]UZ,radio,41

(bootloader) [RUU]UZ,radio,50

(bootloader) [RUU]UZ,radio,59

(bootloader) [RUU]UZ,radio,64

(bootloader) [RUU]UZ,radio,73

(bootloader) [RUU]UZ,radio,82

(bootloader) [RUU]UZ,radio,91

(bootloader) [RUU]UZ,radio,100

(bootloader) trying to rename MBA

(bootloader) [RUU]WP,radio,0

(bootloader) [RUU]WP,radio,36

(bootloader) [RUU]WP,radio,73

(bootloader) [RUU]WP,radio,100

(bootloader) ...... Successful

(bootloader) current_image_number=4

(bootloader) start image[rcdata] unzipping & flushing...

(bootloader) [RUU]UZ,rcdata,0

(bootloader) [RUU]UZ,rcdata,100

(bootloader) [RUU]WP,rcdata,0

(bootloader) [RUU]WP,rcdata,100

(bootloader) ...... Successful

(bootloader) current_image_number=5

OKAY [ 11.820s]

finished. total time: 14.182s

C:\adb>fastboot reboot

rebooting...

finished. total time: 0.000s

C:\adb>adb reboot bootloader

C:\adb>fastboot getvar all

(bootloader) version: 0.5

(bootloader) version-bootloader: 3.19.0.0000

(bootloader) version-baseband: 1.09.20.1112

(bootloader) version-cpld: None

(bootloader) version-microp: None

(bootloader) version-main: 6.20.651.3

(bootloader) version-misc: PVT SHIP S-OFF

(bootloader) serialno: HTxxxxxxxxxxxxx

(bootloader) imei: ..............................

(bootloader) imei2: Not Support

(bootloader) meid: ..............................................

(bootloader) product: m8_whl

(bootloader) platform: hTCBmsm8974

(bootloader) modelid: 0P6B70000

(bootloader) cidnum: 11111111

(bootloader) battery-status: good

(bootloader) battery-voltage: 0mV

(bootloader) partition-layout: Generic

(bootloader) security: off

(bootloader) build-mode: SHIP

(bootloader) boot-mode: FASTBOOT

(bootloader) commitno-bootloader: 205bdca3

(bootloader) hbootpreupdate: 11

(bootloader) gencheckpt: 0

all: Done!

finished. total time: 0.037s

C:\adb>