pcsx2/common/src/x86emitter/jmp.cpp

/*  Pcsx2 - Pc Ps2 Emulator
 *  Copyright (C) 2002-2009  Pcsx2 Team
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *  
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *  
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 */

/*
 * ix86 core v0.9.0
 *
 * Original Authors (v0.6.2 and prior):
 *		linuzappz <linuzappz@pcsx.net>
 *		alexey silinov
 *		goldfinger
 *		zerofrog(@gmail.com)
 *
 * Authors of v0.9.0:
 *		Jake.Stine(@gmail.com)
 *		cottonvibes(@gmail.com)
 *		sudonim(1@gmail.com)
 */

#include "PrecompiledHeader.h"
#include "internal.h"

namespace x86Emitter {

using namespace Internal;

const xImpl_JmpCall<true> xJMP;
const xImpl_JmpCall<false> xCALL;

// ------------------------------------------------------------------------
void xSmartJump::SetTarget()
{
	u8* target = xGetPtr();
	if( m_baseptr == NULL ) return;

	xSetPtr( m_baseptr );
	u8* const saveme = m_baseptr + GetMaxInstructionSize();
	xJccKnownTarget( m_cc, target, true );

	// Copy recompiled data inward if the jump instruction didn't fill the
	// alloted buffer (means that we optimized things to a j8!)

	const int spacer = (sptr)saveme - (sptr)xGetPtr();
	if( spacer != 0 )
	{
		u8* destpos = xGetPtr();
		const int copylen = (sptr)target - (sptr)saveme;

		memcpy_fast( destpos, saveme, copylen );
		xSetPtr( target - spacer );
	}
}

xSmartJump::~xSmartJump()
{
	SetTarget();
	m_baseptr = NULL;	// just in case (sometimes helps in debugging too)
}

// ------------------------------------------------------------------------
// Emits a 32 bit jump, and returns a pointer to the 32 bit displacement.
// (displacements should be assigned relative to the end of the jump instruction,
// or in other words *(retval+1) )
__emitinline s32* xJcc32( JccComparisonType comparison, s32 displacement )
{
	if( comparison == Jcc_Unconditional )
		xWrite8( 0xe9 );
	else
	{
		xWrite8( 0x0f );
		xWrite8( 0x80 | comparison );
	}
	xWrite<s32>( displacement );

	return ((s32*)xGetPtr()) - 1;
}

// ------------------------------------------------------------------------
// Emits a 32 bit jump, and returns a pointer to the 8 bit displacement.
// (displacements should be assigned relative to the end of the jump instruction,
// or in other words *(retval+1) )
__emitinline s8* xJcc8( JccComparisonType comparison, s8 displacement )
{
	xWrite8( (comparison == Jcc_Unconditional) ? 0xeb : (0x70 | comparison) );
	xWrite<s8>( displacement );
	return (s8*)xGetPtr() - 1;
}

// ------------------------------------------------------------------------
// Writes a jump at the current x86Ptr, which targets a pre-established target address.
// (usually a backwards jump)
//
// slideForward - used internally by xSmartJump to indicate that the jump target is going
// to slide forward in the event of an 8 bit displacement.
//
__emitinline void Internal::xJccKnownTarget( JccComparisonType comparison, const void* target, bool slideForward )
{
	// Calculate the potential j8 displacement first, assuming an instruction length of 2:
	sptr displacement8 = (sptr)target - (sptr)(xGetPtr() + 2);

	const int slideVal = slideForward ? ((comparison == Jcc_Unconditional) ? 3 : 4) : 0;
	displacement8 -= slideVal;

	// if the following assert fails it means we accidentally used slideForard on a backward
	// jump (which is an invalid operation since there's nothing to slide forward).
	if( slideForward ) 
	{
		// jASSUME has an  else statement in it that would be abiguous without the brackets.
		jASSUME( displacement8 >= 0 );
	}
	
	if( is_s8( displacement8 ) )
		xJcc8( comparison, displacement8 );
	else
	{
		// Perform a 32 bit jump instead. :(
		s32* bah = xJcc32( comparison );
		*bah = (s32)target - (s32)xGetPtr();
	}
}

// Low-level jump instruction!  Specify a comparison type and a target in void* form, and
// a jump (either 8 or 32 bit) is generated.
__emitinline void xJcc( JccComparisonType comparison, const void* target )
{
	xJccKnownTarget( comparison, target, false );
}

}