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#include "task.h"
#include <assert.h>
#include <stdio.h>

// 3B frame fudger

//Frames not self-describing!
//STACK GROWS UP

typedef unsigned char MACHINE_BYTE;

#ifdef u3b

#define OLD_FP(fp)	( *( (int*)(fp) - 11 ) )
#define OLD_AP(fp)	( *( (int*)(fp) - 12 ) )
#define OLD_PC(fp)	( *( (int*)(fp) - 13 ) )
#define FIRST_SAVED_REG_P(fp)	( (int*)(fp) - 6 )

const CALL_OPCODE = ((MACHINE_BYTE)0x78);
			/* SAK:  really: 0x78 | 0x79 | 0xB9 | 0x77 */
const SAVE_OPCODE = ((MACHINE_BYTE)0x7A);
const BYTE_DISPL	= 0xC0;	/* SAK: WRONG for u3b! */
const HALFWORD_DISPL	= 0xA0;	/* SAK: WRONG for u3b! */
const WORD_DISPL	= 0x80;	/* SAK: WRONG for u3b! */
const ABSOLUTE		= 0x70;	/* SAK: WRONG for u3b! */

const N_CALL_INSTR_SIZES = 6;	/* SAK: WRONG for u3b! */
short call_size[N_CALL_INSTR_SIZES] = {5, 6, 7, 8, 9, 11};	/* SAK: WRONG for u3b! */

/* SAK: SAVE_OPERAND(instr) not needed for u3b */

/* Given a pointer to a save instruction, yield the number of registers saved */
#define N_SAVED_REGS(instr)	(((char *)(instr))[1] >> 4)

/* CALL's src operand descriptor needed to determine size of src operand */
#define SRC_OP_DESC(instr)	(((char *)(instr))[1] & 0xf0)
#define SRC_OP_SIZE(desc) /* assumes sp-relative displacement */\
	(((desc) == BYTE_DISPL)		? 2 :	\
	 ((desc) == HALFWORD_DISPL)	? 3 :	\
	 ((desc) == WORD_DISPL)		? 5 :	\
	 ((((object*)0)->task_error(E_FRAMES)))		\
	)
const	OPCODE_SIZE = 1;
const	DESC_SIZE = 1;

/* SAK:  WRONG for u3b! */
#define	DST_OP_DESC(instr)	\
	(((char *)(instr))[OPCODE_SIZE + SRC_OP_SIZE(SRC_OP_DESC(instr))] & 0xf0)

/* SAK:  WRONG for u3b! */
#define IS_LEGAL_SRC_OP(desc)			\
	(((desc) == BYTE_DISPL)		||	\
	 ((desc) == HALFWORD_DISPL)	||	\
	 ((desc) == WORD_DISPL)			\
	)
/* SAK:  WRONG for u3b! */
#define IS_LEGAL_DST_OP(desc)			\
	(((desc) == BYTE_DISPL)		||	\
	 ((desc) == HALFWORD_DISPL)	||	\
	 ((desc) == WORD_DISPL)		||	\
	 ((desc) == ABSOLUTE)			\
	)


#else	/* m32:  u3b2, u3b5, u3b15 */
#define OLD_FP(fp)	( *( (int*)(fp) - 7 ) )
#define OLD_AP(fp)	( *( (int*)(fp) - 8 ) )
#define OLD_PC(fp)	( *( (int*)(fp) - 9 ) )	
#define FIRST_SAVED_REG_P(fp)	( (int*)(fp) - 6 )
    /*
     * On the 3B2, the call instruction is CALL src,dst
     * where src is the address of the new ap (where the args were
     * already pushed on the stack) and dst is the address of the
     * called function.  src and dst can be various lengths:
     * src will be a byte, halfword, or word displacement
     * and dst will be absolute, or be a byte, halfword, or word displacement.
     * Byte displacement = 2 bytes, halfword = 3, word = 5; the opcode = 1 byte;
     * absolute = 5 bytes--12 possible combinations and 6 possible instr lengths.
     */


const CALL_OPCODE = ((MACHINE_BYTE)0x2c);
const SAVE_OPCODE = ((MACHINE_BYTE)0x10);
const BYTE_DISPL	= 0xC0;
const HALFWORD_DISPL	= 0xA0;
const WORD_DISPL	= 0x80;
const ABSOLUTE		= 0x70;

const N_CALL_INSTR_SIZES = 6;
short call_size[N_CALL_INSTR_SIZES] = {5, 6, 7, 8, 9, 11};

#define SAVE_OPERAND(instr)	(((char *)(instr))[1] & 0xf)

/* Given a pointer to a save instruction, yield the number of registers saved */
#define N_SAVED_REGS(instr)	(8 - SAVE_OPERAND(instr) + 1)

/* CALL's src operand descriptor needed to determine size of src operand */
#define SRC_OP_DESC(instr)	(((char *)(instr))[1] & 0xf0)
#define SRC_OP_SIZE(desc) /* assumes sp-relative displacement */\
	(((desc) == BYTE_DISPL)		? 2 :	\
	 ((desc) == HALFWORD_DISPL)	? 3 :	\
	 ((desc) == WORD_DISPL)		? 5 :	\
	 ((((object*)0)->task_error(E_FRAMES)))		\
	)
const	OPCODE_SIZE = 1;
const	DESC_SIZE = 1;

#define	DST_OP_DESC(instr)	\
	(((char *)(instr))[OPCODE_SIZE + SRC_OP_SIZE(SRC_OP_DESC(instr))] & 0xf0)

#define IS_LEGAL_SRC_OP(desc)			\
	(((desc) == BYTE_DISPL)		||	\
	 ((desc) == HALFWORD_DISPL)	||	\
	 ((desc) == WORD_DISPL)			\
	)
#define IS_LEGAL_DST_OP(desc)			\
	(((desc) == BYTE_DISPL)		||	\
	 ((desc) == HALFWORD_DISPL)	||	\
	 ((desc) == WORD_DISPL)		||	\
	 ((desc) == ABSOLUTE)			\
	)

/* Given a pointer to a call instruction, yield a pointer to the called function */
unsigned int
call_dst_ptr(unsigned char* callp)
{
    int sop_size = SRC_OP_SIZE(SRC_OP_DESC(callp));
    unsigned char* dst_op_p = /* points past the dst desc, to addr or offset */
	callp + OPCODE_SIZE + sop_size + DESC_SIZE;
    int offset;		// offset for displacement modes
    switch(DST_OP_DESC(callp)) {
    case BYTE_DISPL:
	offset = dst_op_p[0];
	if(*dst_op_p & 0x80) {	/* negative--do sign extension for offset */
	    offset |= 0xffffff00;
	}
	return (unsigned int)(callp + offset);
    case HALFWORD_DISPL:
	// bytes are in reverse order, must flip positions
	offset = dst_op_p[0] | dst_op_p[1] << 8;
	if(dst_op_p[1] & 0x80) {	/* negative--do sign extension for offset */
	    offset |= 0xffff0000;
	}
	return (unsigned int)(callp + offset);
    case WORD_DISPL:
	// bytes are in reverse order, must flip positions
	offset = dst_op_p[0]       |
		 dst_op_p[1] <<  8 |
		 dst_op_p[2] << 16 |
		 dst_op_p[3] << 24;
	/* don't need sign extension */
	return (unsigned int)(callp + offset);
    case ABSOLUTE:
	return
	    dst_op_p[0]       |
	    dst_op_p[1] <<  8 |
	    dst_op_p[2] << 16 |
	    dst_op_p[3] << 24;
    default:
	((object*)0)->task_error(E_FRAMES);
    }
}


#endif


struct FrameLayout {
    short   n_saved;	// number of registers saved in this frame.
			// (3B's don't have masks of regs saved)
	    FrameLayout(int*);	// called with frame pointer
};

FrameLayout::FrameLayout(int* fp)
{
    /*
     * Given a frame pointer, find the number of regs saved in the frame.
     * The idea is that the instruction immediately before the return pc
     * is the function call, and contains a pointer to the first instruction
     * in the function denoted by the fp, which will be a save instruction.
     * We can decode the save instruction to find how many registers
     * were saved.
     */

    int*   return_pc = (int*)OLD_PC(fp);

    char* callp = NULL;
    /* Because this method is nondeterministic, try all combinations
       instead of stopping when one fits */
    for(int i = 0; i < N_CALL_INSTR_SIZES; i++) {
        char* poss_callp = (char *)return_pc - call_size[i];
	if ((*poss_callp == CALL_OPCODE)
	     && IS_LEGAL_SRC_OP((SRC_OP_DESC(poss_callp)))
	     && IS_LEGAL_DST_OP((DST_OP_DESC(poss_callp)))) {
	    if(!callp) callp = poss_callp;
	    else ((object*)0)->task_error(E_FRAMES);	//ambiguous; can't tell which
						//is real call.
	}
    }
    if (callp == NULL) ((object*)0)->task_error(E_FRAMES);	//No match!
    assert( *(char *)(call_dst_ptr(callp)) == SAVE_OPCODE);
    n_saved = N_SAVED_REGS(call_dst_ptr(callp));
}

/*
 * fix a frame so that it returns like the arg
 * The idea is that task_fp points to the task::task() stack frame which
 * contains all the saved registers.  t_framep points to the stack frame
 * that contains the return address and old fp (and perhaps some registers).
 * fill the frame pointed to by t_framep with the registers from task_fp.
 */
void
task::fudge_return(int* task_fp, int offset, task* next)
{
	int*	fp = t_framep + offset;
	task_fp += offset;		// in case this is SHARED
	FrameLayout	this_lo(fp);
	FrameLayout	task_lo(task_fp);
	if (task_lo.n_saved != 6)	// task::task() saves all regs
		task_error(E_FUDGE);
	// copy any saved registers from this to task frame
	register int*	task_rp = FIRST_SAVED_REG_P(task_fp) +
			task_lo.n_saved - this_lo.n_saved;
	register int*	this_rp = FIRST_SAVED_REG_P(fp);
	register int	count;
	for (count = this_lo.n_saved; count--; )
		*task_rp++ = *this_rp++;
	// next copy all the registers from the task frame to this
	task_rp = FIRST_SAVED_REG_P(task_fp);
	this_rp = FIRST_SAVED_REG_P(fp);
	for (count = task_lo.n_saved; count--; )
		*this_rp++ = *task_rp++;
	if (next) next->restore();
}

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