/*
 * E-UAE - The portable Amiga Emulator
 *
 * Support for traps
 *
 * Copyright Richard Drummond 2005
 *
 * Inspired by code from UAE:
 * Copyright 1995, 1996 Bernd Schmidt
 * Copyright 1996 Ed Hanway
 */

#include "sysconfig.h"
#include "sysdeps.h"

#include "options.h"
#include "memory.h"
#include "custom.h"
#include "newcpu.h"
#include "threaddep/thread.h"
#include "autoconf.h"
#include "traps.h"

/*
 * Traps are the mechanism via which 68k code can call emulator code
 * (and for that emulator code in turn to call 68k code). They are
 * thus the basis for much of the cool stuff that E-UAE can do.
 *
 * Emulator traps take advantage of the illegal 68k opwords 0xA000 to
 * 0xAFFF. Normally these would generate an A-line exception. However,
 * when encountered in the RTAREA section of memory, these opwords
 * instead invoke a corresponding emulator trap, allowing a host
 * function to be called.
 *
 * Two types of emulator trap are available - a simple trap and an
 * extended trap. A simple trap may not call 68k code; an extended
 * trap can.
 *
 * Extended traps are rather complex beasts (to implement, not
 * necessarily to use). This is because for the trap handler function
 * to be able to call 68k code, we must somehow allow the emulator's
 * 68k interpreter to resume execution of 68k code in the middle of
 * the trap handler function.
 *
 * In UAE of old this used to be implemented via a stack-swap mechanism.
 * While this worked, it was definitely in the realm of black magic and
 * horribly non-portable, requiring assembly language glue specific to
 * the host ABI and compiler to actually perform the swap.
 *
 * In this implementation, in essence we do something similar - but the
 * new stack is provided by a new thread. No voodoo required, just a
 * working thread layer.
 *
 * The complexity in this approach arises in synchronizing the trap
 * threads with the emulator thread. This implementation errs on the side
 * of paranoia when it comes to thread synchronization. Once all the
 * bugs are knocked out of the bsdsocket emulation, a simpler scheme may
 * suffice.
 */

/*
 * Record of a defined trap (that is, a trap allocated to a host function)
 */
struct Trap
{
	TrapHandler handler;	/* Handler function to be invoked for this trap. */
	int         flags;		/* Trap attributes. */
	const TCHAR *name;		/* For debugging purposes. */
	uaecptr addr;
};

#define MAX_TRAPS 4096

/* Defined traps */
static struct Trap  traps[MAX_TRAPS];
static unsigned int trap_count = 1;


static const int trace_traps = 0;

static void trap_HandleExtendedTrap (TrapHandler, int has_retval);

uaecptr find_trap (const TCHAR *name)
{
	int i;

	for (i = 0; i < trap_count; i++) {
		struct Trap *trap = &traps[i];
		if ((trap->flags & TRAPFLAG_UAERES) && trap->name && !_tcscmp (trap->name, name))
			return trap->addr;
	}
	return 0;
}


/*
 * Define an emulator trap
 *
 * handler_func = host function that will be invoked to handle this trap
 * flags        = trap attributes
 * name         = name for debugging purposes
 *
 * returns trap number of defined trap
 */
unsigned int define_trap (TrapHandler handler_func, int flags, const TCHAR *name)
{
	if (trap_count == MAX_TRAPS) {
		write_log ("Ran out of emulator traps\n");
		abort ();
		return -1;
	} else {
		int i;
		unsigned int trap_num;
		struct Trap *trap;
		uaecptr addr = here ();

		for (i = 0; i < trap_count; i++) {
			if (addr == traps[i].addr)
				return i;
		}

		trap_num = trap_count++;
		trap = &traps[trap_num];

		trap->handler = handler_func;
		trap->flags   = flags;
		trap->name    = name;
		trap->addr    = addr;

		return trap_num;
	}
}


/*
 * This function is called by the 68k interpreter to handle an emulator trap.
 *
 * trap_num = number of trap to invoke
 * regs     = current 68k state
 */
void REGPARAM2 m68k_handle_trap (unsigned int trap_num)
{
	struct Trap *trap = &traps[trap_num];
	uae_u32 retval = 0;

	int has_retval = (trap->flags & TRAPFLAG_NO_RETVAL) == 0;
	int implicit_rts = (trap->flags & TRAPFLAG_DORET) != 0;

	if (trap->name && trap->name[0] != 0 && trace_traps)
		write_log ("TRAP: %s\n", trap->name);

	if (trap_num < trap_count) {
		if (trap->flags & TRAPFLAG_EXTRA_STACK) {
			/* Handle an extended trap.
			 * Note: the return value of this trap is passed back to 68k
			 * space via a separate, dedicated simple trap which the trap
			 * handler causes to be invoked when it is done.
			 */
			trap_HandleExtendedTrap (trap->handler, has_retval);
		} else {
			/* Handle simple trap */
			retval = (trap->handler) (NULL);

			if (has_retval)
				m68k_dreg (regs, 0) = retval;

			if (implicit_rts) {
				m68k_do_rts ();
				fill_prefetch ();
			}
		}
	} else
		write_log ("Illegal emulator trap %d\n", trap_num);
}



/*
 * Implementation of extended traps
 */

struct TrapContext
{
	/* Trap's working copy of 68k state. This is what the trap handler should
	* access to get arguments from 68k space. */
	struct regstruct regs;

	/* Trap handler function that gets called on the trap context */
	TrapHandler trap_handler;
	/* Should the handler return a value to 68k space in D0? */
	int trap_has_retval;
	/* Return value from trap handler */
	uae_u32 trap_retval;

	/* Copy of 68k state at trap entry. */
	struct regstruct saved_regs;

	/* Thread which effects the trap context. */
	uae_thread_id thread;
	/* For IPC between the main emulator. */
	uae_sem_t switch_to_emu_sem;
	/* context and the trap context. */
	uae_sem_t switch_to_trap_sem;

	/* When calling a 68k function from a trap handler, this is set to the
	* address of the function to call.  */
	uaecptr call68k_func_addr;
	/* And this gets set to the return value of the 68k call.  */
	uae_u32 call68k_retval;
};


/* 68k addresses which invoke the corresponding traps. */
static uaecptr m68k_call_trapaddr;
static uaecptr m68k_return_trapaddr;
static uaecptr exit_trap_trapaddr;

/* For IPC between main thread and trap context */
static uae_sem_t trap_mutex;
static TrapContext *current_context;


/*
 * Thread body for trap context
 */
static void *trap_thread (void *arg)
{
	TrapContext *context = (TrapContext *) arg;

	/* Wait until main thread is ready to switch to the
	 * this trap context. */
	uae_sem_wait (&context->switch_to_trap_sem);

	/* Execute trap handler function. */
	context->trap_retval = context->trap_handler (context);

	/* Trap handler is done - we still need to tidy up
	 * and make sure the handler's return value is propagated
	 * to the calling 68k thread.
	 *
	 * We do this by causing our exit handler to be executed on the 68k context.
	 */

	/* Enter critical section - only one trap at a time, please! */
	uae_sem_wait (&trap_mutex);

	regs = context->saved_regs;
	/* Don't allow an interrupt and thus potentially another
	 * trap to be invoked while we hold the above mutex.
	 * This is probably just being paranoid. */
	regs.intmask = 7;

	/* Set PC to address of the exit handler, so that it will be called
	 * when the 68k context resumes. */
	m68k_setpc (exit_trap_trapaddr);
	current_context = context;

	/* Switch back to 68k context */
	uae_sem_post (&context->switch_to_emu_sem);

	/* Good bye, cruel world... */

	/* dummy return value */
	return 0;
}

/*
 * Set up extended trap context and call handler function
 */
static void trap_HandleExtendedTrap (TrapHandler handler_func, int has_retval)
{
	struct TrapContext *context = xcalloc (TrapContext, 1);

	if (context) {
		uae_sem_init (&context->switch_to_trap_sem, 0, 0);
		uae_sem_init (&context->switch_to_emu_sem, 0, 0);

		context->trap_handler = handler_func;
		context->trap_has_retval = has_retval;

		context->saved_regs = regs; /* Copy of regs to be restored when trap is done */

		/* Start thread to handle new trap context. */
		uae_start_thread ("Trap", trap_thread, (void *)context, &context->thread);

		/* Switch to trap context to begin execution of
		 * trap handler function.
		 */
		uae_sem_post (&context->switch_to_trap_sem);

		/* Wait for trap context to switch back to us.
		 *
		 * It'll do this when the trap handler is done - or when
		 * the handler wants to call 68k code. */
		uae_sem_wait (&context->switch_to_emu_sem);
	}
}

/*
 * Call m68k function from an extended trap handler
 *
 * This function is to be called from the trap context.
 */
static uae_u32 trap_Call68k (TrapContext *context, uaecptr func_addr)
{
	/* Enter critical section - only one trap at a time, please! */
	uae_sem_wait (&trap_mutex);
	current_context = context;

	/* Don't allow an interrupt and thus potentially another
	 * trap to be invoked while we hold the above mutex.
	 * This is probably just being paranoid. */
	regs.intmask = 7;

	/* Set up function call address. */
	context->call68k_func_addr = func_addr;

	/* Set PC to address of 68k call trap, so that it will be
	 * executed when emulator context resumes. */
	m68k_setpc (m68k_call_trapaddr);
	fill_prefetch ();

	/* Switch to emulator context. */
	uae_sem_post (&context->switch_to_emu_sem);

	/* Wait for 68k call return handler to switch back to us. */
	uae_sem_wait (&context->switch_to_trap_sem);

	/* End critical section. */
	uae_sem_post (&trap_mutex);

	/* Get return value from 68k function called. */
	return context->call68k_retval;
}

/*
 * Handles the emulator's side of a 68k call (from an extended trap)
 */
static uae_u32 REGPARAM3 m68k_call_handler (TrapContext *dummy_ctx)
{
	TrapContext *context = current_context;

	uae_u32 sp;

	sp = m68k_areg (regs, 7);

	/* Push address of trap context on 68k stack. This is
	 * so the return trap can find this context. */
	sp -= sizeof (void *);
	put_pointer (sp, context);

	/* Push addr to return handler trap on 68k stack.
	 * When the called m68k function does an RTS, the CPU will pull this
	 * address off the stack and so call the return handler. */
	sp -= 4;
	put_long (sp, m68k_return_trapaddr);

	m68k_areg (regs, 7) = sp;

	/* Set PC to address of 68k function to call. */
	m68k_setpc (context->call68k_func_addr);
	fill_prefetch ();

	/* End critical section: allow other traps run. */
	uae_sem_post (&trap_mutex);

	/* Restore interrupts. */
	regs.intmask = context->saved_regs.intmask;

	/* Dummy return value. */
	return 0;
}

/*
 * Handles the return from a 68k call at the emulator's side.
 */
static uae_u32 REGPARAM3 m68k_return_handler (TrapContext *dummy_ctx)
{
	TrapContext *context;
	uae_u32 sp;

	/* One trap returning at a time, please! */
	uae_sem_wait (&trap_mutex);

	/* Get trap context from 68k stack. */
	sp = m68k_areg (regs, 7);
	context = (TrapContext *)get_pointer (sp);
	sp += sizeof (void *);
	m68k_areg (regs, 7) = sp;

	/* Get return value from the 68k call. */
	context->call68k_retval = m68k_dreg (regs, 0);

	/* Switch back to trap context. */
	uae_sem_post (&context->switch_to_trap_sem);

	/* Wait for trap context to switch back to us.
	 *
	 * It'll do this when the trap handler is done - or when
	 * the handler wants to call another 68k function. */
	uae_sem_wait (&context->switch_to_emu_sem);

	/* Dummy return value. */
	return 0;
}

/*
 * Handles completion of an extended trap and passes
 * return value from trap function to 68k space.
 */
static uae_u32 REGPARAM3 exit_trap_handler (TrapContext *dummy_ctx)
{
	TrapContext *context = current_context;

	/* Wait for trap context thread to exit. */
	uae_wait_thread (context->thread);

	/* Restore 68k state saved at trap entry. */
	regs = context->saved_regs;

	/* If trap is supposed to return a value, then store
	 * return value in D0. */
	if (context->trap_has_retval)
		m68k_dreg (regs, 0) = context->trap_retval;

	uae_sem_destroy (&context->switch_to_trap_sem);
	uae_sem_destroy (&context->switch_to_emu_sem);

	xfree (context);

	/* End critical section */
	uae_sem_post (&trap_mutex);

	/* Dummy return value. */
	return 0;
}



/*
 * Call a 68k library function from extended trap.
 */
uae_u32 CallLib (TrapContext *context, uaecptr base, uae_s16 offset)
{
	uae_u32 retval;
	uaecptr olda6 = m68k_areg (regs, 6);

	m68k_areg (regs, 6) = base;
	retval = trap_Call68k (context, base + offset);
	m68k_areg (regs, 6) = olda6;

	return retval;
}

/*
 * Call 68k function from extended trap.
 */
uae_u32 CallFunc (TrapContext *context, uaecptr func)
{
	return trap_Call68k (context, func);
}


/*
 * Initialize trap mechanism.
 */
void init_traps (void)
{
	trap_count = 0;
}

/*
 * Initialize the extended trap mechanism.
 */
void init_extended_traps (void)
{
	m68k_call_trapaddr = here ();
	calltrap (deftrap2 (m68k_call_handler, TRAPFLAG_NO_RETVAL, "m68k_call"));

	m68k_return_trapaddr = here();
	calltrap (deftrap2 (m68k_return_handler, TRAPFLAG_NO_RETVAL, "m68k_return"));

	exit_trap_trapaddr = here();
	calltrap (deftrap2 (exit_trap_handler, TRAPFLAG_NO_RETVAL, "exit_trap"));

	uae_sem_init (&trap_mutex, 0, 1);
}
