Hisense U6H - magiskinit fails b/c bootloader adds skip_initramfs on 2SI device

[latelylk]

Device: Hisense U6H
Android version: 11
Magisk version name: 81658d4
Magisk version code: 27002

In October 2023 I was successful in patching the boot image, but faced a black screen and no OS when trying to boot from it. The debug logs showed that Magisk was seeing skip_initramfs in the patched image of our 2SI device:

[ 5.742326] magiskinit: Device config:
[ 5.746102] magiskinit: skip_initramfs=[1]
[ 5.750236] magiskinit: force_normal_boot=[0]

Magisk normally patches skip_initramfs out of the boot image. At some point in the past devices (ex: Galaxy A21s) started having skip_initramfs added to the dtb bootargs. Magisk v24.0 fixed this by patching the dtb. Similar to how that issue presented, magiskinit treats the Hisense U6H as a Legacy SAR device because skip_initramfs is added by U-Boot (MBOOT).

Special thanks to @throwaway96 for finding this. Hisense adds skip_initramfs in the bootloader (0x274F108C):

void env_add_boot_skip_initramfs(void)
{
    const char boot_skip_initramfs[] = "skip_initramfs";
    env_add_bootargs(boot_skip_initramfs, boot_skip_initramfs);
}

it does this with a check in the do_readKL() function (0x274F1654):

// append command line.
if(strcmp(partition_name,"boot") == 0)
{
    env_add_boot_skip_initramfs();
}

Luckily with this understanding we can easily patch Magisk to achieve root:

Patching Magisk :)

Prereqs: - [Magisk v27.0 Source](https://github.com/topjohnwu/Magisk/releases/tag/v27.0)* - Ability to compile Magisk

1. Edit lines 85-87 of native/src/init/init.cpp from:

if (config.skip_initramfs)
  init = new LegacySARInit(argv, &config);
else if (config.force_normal_boot)

to:

/*if (config.skip_initramfs)
    init = new LegacySARInit(argv, &config);
else*/ if (config.force_normal_boot)

2. That's it. Compile and use Magisk as normal. Have fun?

A similar issue to this was created when Galaxy A21s devices began including skip_initramfs in the dtb (xda, #4307). In that issue osm0sis stated:

Creating a device/board whitelist is not a proper solution

I'm not sure what Magisk can do to solve this without hardcoding for these devices. Patching the bootloader seems risky. Depending on how other devices are structured, can the order for checking skip_initramfs and force_normal_boot be swapped? Any other ideas?

Thank you :)

Quick reference:
Hisense U6H XDA Thread
Patching Magisk for Galaxy A21s XDA Thread
#4307

tl;dr Assumptions that Magisk makes should be correct, but the patches Hisense have applied to U-Boot make that not so

[yujincheng08]

How about moving

Magisk/native/src/init/init.cpp

Lines 96 to 97 in c6f0762

	else if (check_two_stage())
	init = new FirstStageInit(argv, &config);

before

Magisk/native/src/init/init.cpp

Lines 90 to 91 in c6f0762

	if (config.skip_initramfs)
	init = new LegacySARInit(argv, &config);

But I dont know if this will break other devices.

[latelylk]

Hi @yujincheng08 just checking whether this is truly "not planned" or if it was closed for being stale. I'll have a device on-hand again soon - am I able to re-open this or open a new issue when I am available to work on it?

[yujincheng08]

it was closed for being stale

[latelylk]

Perfect. Thank you :)