The idle stack area started at _ebss + CONFIG_IDLETHREAD_STACKSIZE *
CONFIG_SMP_NCPUS, so the first CONFIG_SMP_NCPUS stack slots after .bss
were never used - 16MiB on a 4-CPU configuration with a 4MiB idle
stack. Start the area at _ebss and let the heap begin that much
earlier.
The -16 offset is kept: it is what places the AP initial RSP set up in
intel64_head.S below the xcp->regs block that up_cpu_idlestack()
reserves at the top of the same stack. Without it both land on the
same 64-byte slot and the first context save corrupts the AP stack.
Signed-off-by: raiden00pl <raiden00@railab.me>
Assisted-by: Claude Code
3be03008ac