kernel: init: option to zero noinit memory

[cfriedt]

Add CONFIG_ZERO_NOINIT_MEMORY to explicitly zero memory regions marked __noinit at startup.

This is useful for systems with ECC memory.

Fixes #39598

[stephanosio]

This is useful for systems with ECC memory.

IMO, that should be handled by the memory subsystem/driver managing that particular ECC memory or by the SoC layer if the ECC memory is part of the SoC.

After all, not properly initialising the ECC-checked memory area (or initialising the ECC data based on the current random content of the ECC-checked memory area) is the memory driver's bug.

[cfriedt]

IMO, that should be handled by the memory subsystem/driver managing that particular ECC memory or by the SoC layer if the ECC memory is part of the SoC.

@stephanosio - Interesting. I'll look into the possibility of upstreaming the memory controller as well, but this change would be required in any event.

After all, not properly initialising the ECC-checked memory area (or initialising the ECC data based on the current random content of the ECC-checked memory area) is the memory driver's bug.

In this case, the ECC controller does not have a way to initialize from a random state so memory must be written at startup. Adding functionality like z_bss_zero() was also suggested previously.

#39599 (review)

Note: __noinit only applies to SRAM regions.

[stephanosio]

AFAIK, we do not yet have such a subsystem/driver.

https://github.com/zephyrproject-rtos/zephyr/tree/main/drivers/memc

Adding functionality like z_bss_zero() was also suggested previously.

ECC memory initialisation is platform and/or memory controller-specific and should be handled by the SoC layer or the memory controller driver.

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