/*
 * Copyright (c) 2013-2014 Wind River Systems, Inc.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * @file
 * @brief New thread creation for ARM Cortex-M
 *
 * Core thread related primitives for the ARM Cortex-M processor architecture.
 */

#include <kernel.h>
#include <toolchain.h>
#include <kernel_structs.h>
#include <wait_q.h>
#ifdef CONFIG_INIT_STACKS
#include <string.h>
#endif /* CONFIG_INIT_STACKS */

#ifdef CONFIG_USERSPACE
extern u8_t *_k_priv_stack_find(void *obj);
#endif

/**
 *
 * @brief Initialize a new thread from its stack space
 *
 * The control structure (thread) is put at the lower address of the stack. An
 * initial context, to be "restored" by __pendsv(), is put at the other end of
 * the stack, and thus reusable by the stack when not needed anymore.
 *
 * The initial context is an exception stack frame (ESF) since exiting the
 * PendSV exception will want to pop an ESF. Interestingly, even if the lsb of
 * an instruction address to jump to must always be set since the CPU always
 * runs in thumb mode, the ESF expects the real address of the instruction,
 * with the lsb *not* set (instructions are always aligned on 16 bit halfwords).
 * Since the compiler automatically sets the lsb of function addresses, we have
 * to unset it manually before storing it in the 'pc' field of the ESF.
 *
 * <options> is currently unused.
 *
 * @param pStackMem the aligned stack memory
 * @param stackSize stack size in bytes
 * @param pEntry the entry point
 * @param parameter1 entry point to the first param
 * @param parameter2 entry point to the second param
 * @param parameter3 entry point to the third param
 * @param priority thread priority
 * @param options thread options: K_ESSENTIAL, K_FP_REGS
 *
 * @return N/A
 */

void _new_thread(struct k_thread *thread, k_thread_stack_t *stack,
		 size_t stackSize, k_thread_entry_t pEntry,
		 void *parameter1, void *parameter2, void *parameter3,
		 int priority, unsigned int options)
{
	char *pStackMem = K_THREAD_STACK_BUFFER(stack);

	_ASSERT_VALID_PRIO(priority, pEntry);

#if CONFIG_MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT
	char *stackEnd = pStackMem + stackSize - MPU_GUARD_ALIGN_AND_SIZE;
#else
	char *stackEnd = pStackMem + stackSize;
#endif
	struct __esf *pInitCtx;

	_new_thread_init(thread, pStackMem, stackEnd - pStackMem, priority,
			 options);

	/* carve the thread entry struct from the "base" of the stack */
	pInitCtx = (struct __esf *)(STACK_ROUND_DOWN(stackEnd -
						     sizeof(struct __esf)));

#if CONFIG_USERSPACE
	if (options & K_USER) {
		pInitCtx->pc = (u32_t)_arch_user_mode_enter;
	} else {
		pInitCtx->pc = (u32_t)_thread_entry;
	}
#else
	pInitCtx->pc = (u32_t)_thread_entry;
#endif

	/* force ARM mode by clearing LSB of address */
	pInitCtx->pc &= 0xfffffffe;

	pInitCtx->a1 = (u32_t)pEntry;
	pInitCtx->a2 = (u32_t)parameter1;
	pInitCtx->a3 = (u32_t)parameter2;
	pInitCtx->a4 = (u32_t)parameter3;
	pInitCtx->xpsr =
		0x01000000UL; /* clear all, thumb bit is 1, even if RO */

	thread->callee_saved.psp = (u32_t)pInitCtx;
	thread->arch.basepri = 0;

#if CONFIG_USERSPACE
	thread->arch.mode = 0;
	thread->arch.priv_stack_start = 0;
	thread->arch.priv_stack_size = 0;
#endif

	/* swap_return_value can contain garbage */

	/*
	 * initial values in all other registers/thread entries are
	 * irrelevant.
	 */
}

#ifdef CONFIG_USERSPACE

FUNC_NORETURN void _arch_user_mode_enter(k_thread_entry_t user_entry,
	void *p1, void *p2, void *p3)
{

	/* Set up privileged stack before entering user mode */
	_current->arch.priv_stack_start =
		(u32_t)_k_priv_stack_find(_current->stack_obj);
	_current->arch.priv_stack_size =
		(u32_t)CONFIG_PRIVILEGED_STACK_SIZE;

	/* FIXME: Need a general API for aligning stacks so thet the initial
	 * user thread stack pointer doesn't overshoot the granularity of MPU
	 * regions, that works for ARM/NXP/QEMU.
	 */
	_current->stack_info.size &= ~0x1f;

	_arm_userspace_enter(user_entry, p1, p2, p3,
			     (u32_t)_current->stack_info.start,
			     _current->stack_info.size);
	CODE_UNREACHABLE;
}

#endif

#if defined(CONFIG_BUILTIN_STACK_GUARD)
/*
 * @brief Configure ARM built-in stack guard
 *
 * This function configures per thread stack guards by reprogramming
 * the built-in Process Stack Pointer Limit Register (PSPLIM).
 *
 * @param thread thread info data structure.
 */
void configure_builtin_stack_guard(struct k_thread *thread)
{
#if defined(CONFIG_USERSPACE)
	u32_t guard_start = thread->arch.priv_stack_start ?
			    (u32_t)thread->arch.priv_stack_start :
			    (u32_t)thread->stack_obj;
#else
	u32_t guard_start = thread->stack_info.start;
#endif
#if defined(CONFIG_CPU_CORTEX_M_HAS_SPLIM)
	__set_PSPLIM(guard_start);
#else
#error "Built-in PSP limit checks not supported by HW"
#endif
}
#endif /* CONFIG_BUILTIN_STACK_GUARD */