> The linux kernel does not follow this part of the ABI, so the compiler needs to be told that there is no red zone or functions will randomly see their stack f

> The linux kernel does not follow this part of the ABI, so the compiler needs to be told that there is no red zone or functions will randomly see their stack frame clobbered by interrupt handlers. You're absolute right, but I would add a qualifier that it is impossible for a kernel to use the redzone optimization. Certain architectures (Like x86) will push data onto the stack when an interrupt happens and there is no way to tell them to put that data after the first 128 bytes on the stack.