RPi5: Kernel fails to boot with CONFIG_INIT_STACK_NONE=y (works with INIT_STACK_ALL_ZERO)

[antonellocaroli]

Describe the bug

I encountered a configuration-dependent issue on Raspberry Pi 5 related to stack initialization.

When using:

CONFIG_INIT_STACK_NONE=y

the system exhibits failures, while switching to:

CONFIG_INIT_STACK_ALL_ZERO=y

resolves the issue completely.

Tested on:

• Raspberry Pi 5
• Kernel: rpi-6.12.y (tested on 6.12.79 and 6.12.83)
• Toolchain: clang (LLVM)
• Custom config derived from bcm2712_defconfig

Behavior:

Kernel 6.12.79:

• System does not reach kernel output
• No visible logs
• Fan remains at high speed (system appears stuck very early in boot)

Kernel 6.12.83:

• System boots
• Networking does not come up

Switching back to:

CONFIG_INIT_STACK_ALL_ZERO=y

restores full functionality, including networking.

The issue is reproducible by changing only:

CONFIG_INIT_STACK_ALL_ZERO y -> n
CONFIG_INIT_STACK_NONE n -> y

This suggests a possible dependency on implicitly zero-initialized stack data in early boot or platform/network initialization code.

Steps to reproduce the behaviour

1. Build kernel for Raspberry Pi 5 using rpi-6.12.y

2. Use a config based on bcm2712_defconfig

3. Set:

   CONFIG_INIT_STACK_NONE=y

4. Boot system

Result:

• Kernel 6.12.79: system hangs very early
• Kernel 6.12.83: system boots but networking is not working

5. Change config to:

   CONFIG_INIT_STACK_ALL_ZERO=y

6. Rebuild and reboot

Result:

• System boots correctly
• Networking works

Device (s)

Raspberry Pi 5

System

OS: Gentoo-based custom system
Kernel: rpi-6.12.y (6.12.79 and 6.12.83)
Toolchain: clang (LLVM)
Firmware: 2026/02/23 10:01:39
Copyright (c) 2012 Broadcom
version 85353ce4 (release) (embedded)

Logs

No response

Additional context

No response