#include "context.h"

#include "../debug/assert.h"
#include "../debug/kernelpanic.h"

/*! \brief Panic function
 *
 * If the kickoff function (assigned in \ref prepareContext) *returns*, this
 * parameterless function will be called -- and stop the execution.
 */
static void panic() {
	// we should not come back here
	kernelpanic("Application should not return from context_kickoff");
}

void prepareContext(void* tos, Context& context,
					void (*kickoff)(uintptr_t, uintptr_t, uintptr_t),
					uintptr_t param1, uintptr_t param2, uintptr_t param3) {
	assert(tos != nullptr && "Top Of Stack must not be nullptr");
	assert((uintptr_t)tos % 16 == 0 && "Top Of Stack be 16 byte aligned");
	assert(kickoff != nullptr && "Kickoff function missing");

	// XXX Double check alignment. This seems to work, but the stack pointer for
	// `panic` should not be aligned to 16-bit?
	void** sp = reinterpret_cast<void**>(tos);
	*(--sp) = reinterpret_cast<void*>(panic);	 // return address
	*(--sp) = reinterpret_cast<void*>(kickoff);	 // start the thread in C land
	*(--sp) = reinterpret_cast<void*>(fake_systemv_abi);  // pass via registers

	context = {
		.rbx = 0,
		.rbp = 0,
		.r12 = 0,
		.r13 = param3,
		.r14 = param2,	// Second parameter to kickoff
		.r15 = param1,	// First parameter to kickoff
		.rsp = reinterpret_cast<void*>(sp),
	};
}