xref: /original-bsd/old/dbx/vax.c (revision 902755c9)

/*
 * Copyright (c) 1983 The Regents of the University of California.
 * All rights reserved.
 *
 * %sccs.include.redist.c%
 */

#ifndef lint
static char sccsid[] = "@(#)vax.c	5.8 (Berkeley) 06/01/90";
#endif /* not lint */

/*
 * Target machine dependent stuff.
 */

#include "defs.h"
#include "machine.h"
#include "process.h"
#include "runtime.h"
#include "events.h"
#include "main.h"
#include "symbols.h"
#include "source.h"
#include "mappings.h"
#include "object.h"
#include "tree.h"
#include "eval.h"
#include "keywords.h"
#include "ops.h"

#ifndef public
typedef unsigned int Address;
typedef unsigned char Byte;
typedef unsigned int Word;

#define NREG 16

#define ARGP 12
#define FRP 13
#define STKP 14
#define PROGCTR 15

#define CODESTART 0
#define FUNCOFFSET 2

#define nargspassed(frame) argn(0, frame)

#define BITSPERBYTE 8
#define BITSPERWORD (BITSPERBYTE * sizeof(Word))

/*
 * This magic macro enables us to look at the process' registers
 * in its user structure.
 */

#define regloc(reg)	(ctob(UPAGES) + (sizeof(Word) * (reg)))

#include "source.h"
#include "symbols.h"
#include <signal.h>
#include <sys/param.h>
#include <machine/psl.h>
#include <machine/pte.h>
#include <sys/user.h>
#undef DELETE /* XXX */
#include <sys/vm.h>
#include <machine/reg.h>

Address pc;
Address prtaddr;

#endif

/*
 * Indices into u. for use in collecting registers values.
 */
public int rloc[] ={
    R0, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, AP, FP, SP, PC
};

private Address printop();

private Optab *ioptab[256];	/* index by opcode to optab */
private Optab *esctab[256];	/* for extended opcodes */

/*
 * Initialize the opcode lookup table.
 */
public optab_init()
{
    register Optab *p;

    for (p = optab; p->iname; p++) {
	if (p->format == O_ESCD) {
	    esctab[p->val] = p;
	} else if (p->format != O_ESCD && p->format != O_ESCE) {
	    ioptab[p->val] = p;
	}
    }
}

/*
 * Decode and print the instructions within the given address range.
 */

public printinst(lowaddr, highaddr)
Address lowaddr;
Address highaddr;
{
    register Address addr;

    for (addr = lowaddr; addr <= highaddr; ) {
	addr = printop(addr);
    }
    prtaddr = addr;
}

/*
 * Another approach:  print n instructions starting at the given address.
 */

public printninst(count, addr)
int count;
Address addr;
{
    register Integer i;
    register Address newaddr;

    if (count <= 0) {
	error("non-positive repetition count");
    } else {
	newaddr = addr;
	for (i = 0; i < count; i++) {
	    newaddr = printop(newaddr);
	}
	prtaddr = newaddr;
    }
}

/*
 * Print the contents of the addresses within the given range
 * according to the given format.
 */

typedef struct {
    String name;
    String printfstring;
    int length;
} Format;

private Format fmt[] = {
    { "d", " %d", sizeof(short) },
    { "D", " %ld", sizeof(long) },
    { "o", " %o", sizeof(short) },
    { "O", " %lo", sizeof(long) },
    { "x", " %04x", sizeof(short) },
    { "X", " %08x", sizeof(long) },
    { "b", " \\%o", sizeof(char) },
    { "c", " '%c'", sizeof(char) },
    { "s", "%c", sizeof(char) },
    { "f", " %f", sizeof(float) },
    { "g", " %g", sizeof(double) },
    { nil, nil, 0 }
};

private Format *findformat(s)
String s;
{
    register Format *f;

    f = &fmt[0];
    while (f->name != nil and not streq(f->name, s)) {
	++f;
    }
    if (f->name == nil) {
	error("bad print format \"%s\"", s);
    }
    return f;
}

/*
 * Retrieve and print out the appropriate data in the given format.
 * Floats have to be handled specially to allow the compiler to
 * convert them to doubles when passing to printf.
 */

private printformat (f, addr)
Format *f;
Address addr;
{
    union {
	char charv;
	short shortv;
	int intv;
	float floatv;
	double doublev;
    } value;

    value.intv = 0;
    dread(&value, addr, f->length);
    if (streq(f->name, "f")) {
	printf(f->printfstring, value.floatv);
    } else {
	printf(f->printfstring, value);
    }
}

public Address printdata(lowaddr, highaddr, format)
Address lowaddr;
Address highaddr;
String format;
{
    int n;
    register Address addr;
    Format *f;

    if (lowaddr > highaddr) {
	error("first address larger than second");
    }
    f = findformat(format);
    n = 0;
    for (addr = lowaddr; addr <= highaddr; addr += f->length) {
	if (n == 0) {
	    printf("%08x: ", addr);
	}
	printformat(f, addr);
	++n;
	if (n >= (16 div f->length)) {
	    printf("\n");
	    n = 0;
	}
    }
    if (n != 0) {
	printf("\n");
    }
    prtaddr = addr;
    return addr;
}

/*
 * The other approach is to print n items starting with a given address.
 */

public printndata(count, startaddr, format)
int count;
Address startaddr;
String format;
{
    int i, n;
    Address addr;
    Format *f;
    Boolean isstring;
    char c;

    if (count <= 0) {
	error("non-positive repetition count");
    }
    f = findformat(format);
    isstring = (Boolean) streq(f->name, "s");
    n = 0;
    addr = startaddr;
    for (i = 0; i < count; i++) {
	if (n == 0) {
	    printf("%08x: ", addr);
	}
	if (isstring) {
	    printf("\"");
	    dread(&c, addr, sizeof(char));
	    while (c != '\0') {
		printchar(c);
		++addr;
		dread(&c, addr, sizeof(char));
	    }
	    printf("\"\n");
	    n = 0;
	    addr += sizeof(String);
	} else {
	    printformat(f, addr);
	    ++n;
	    if (n >= (16 div f->length)) {
		printf("\n");
		n = 0;
	    }
	    addr += f->length;
	}
    }
    if (n != 0) {
	printf("\n");
    }
    prtaddr = addr;
}

/*
 * Print out a value according to the given format.
 */

public printvalue(v, format)
long v;
String format;
{
    Format *f;
    char *p, *q;

    f = findformat(format);
    if (streq(f->name, "s")) {
	putchar('"');
	p = (char *) &v;
	q = p + sizeof(v);
	while (p < q) {
	    printchar(*p);
	    ++p;
	}
	putchar('"');
    } else {
	printf(f->printfstring, v);
    }
    putchar('\n');
}

/*
 * Print out an execution time error.
 * Assumes the source position of the error has been calculated.
 *
 * Have to check if the -r option was specified; if so then
 * the object file information hasn't been read in yet.
 */

public printerror()
{
    extern Integer sys_nsig;
    extern String sys_siglist[];
    integer err;

    if (isfinished(process)) {
	err = exitcode(process);
	if (err == 0) {
	    printf("\"%s\" terminated normally\n", objname);
	} else {
	    printf("\"%s\" terminated abnormally (exit code %d)\n",
		objname, err
	    );
	}
	erecover();
    }
    err = errnum(process);
    putchar('\n');
    printsig(err);
    putchar(' ');
    printloc();
    putchar('\n');
    if (curline > 0) {
	printlines(curline, curline);
    } else {
	printinst(pc, pc);
    }
    erecover();
}

/*
 * Print out a signal.
 */

private String illinames[] = {
    "reserved addressing fault",
    "privileged instruction fault",
    "reserved operand fault"
};

private String fpenames[] = {
    nil,
    "integer overflow trap",
    "integer divide by zero trap",
    "floating overflow trap",
    "floating/decimal divide by zero trap",
    "floating underflow trap",
    "decimal overflow trap",
    "subscript out of range trap",
    "floating overflow fault",
    "floating divide by zero fault",
    "floating underflow fault"
};

public printsig (signo)
integer signo;
{
    integer code;

    if (signo < 0 or signo > sys_nsig) {
	printf("[signal %d]", signo);
    } else {
	printf("%s", sys_siglist[signo]);
    }
    code = errcode(process);
    if (signo == SIGILL) {
	if (code >= 0 and code < sizeof(illinames) / sizeof(illinames[0])) {
	    printf(" (%s)", illinames[code]);
	}
    } else if (signo == SIGFPE) {
	if (code > 0 and code < sizeof(fpenames) / sizeof(fpenames[0])) {
	    printf(" (%s)", fpenames[code]);
	}
    }
}

/*
 * Note the termination of the program.  We do this so as to avoid
 * having the process exit, which would make the values of variables
 * inaccessible.  We do want to flush all output buffers here,
 * otherwise it'll never get done.
 */

public endprogram()
{
    Integer exitcode;

    stepto(nextaddr(pc, true));
    printnews();
    exitcode = argn(1, nil);
    if (exitcode != 0) {
	printf("\nexecution completed (exit code %d)\n", exitcode);
    } else {
	printf("\nexecution completed\n");
    }
    getsrcpos();
    erecover();
}

/*
 * Single step the machine a source line (or instruction if "inst_tracing"
 * is true).  If "isnext" is true, skip over procedure calls.
 */

private Address getcall();

public dostep(isnext)
Boolean isnext;
{
    register Address addr;
    register Lineno line;
    String filename;
    Address startaddr;

    startaddr = pc;
    addr = nextaddr(pc, isnext);
    if (not inst_tracing and nlhdr.nlines != 0) {
	line = linelookup(addr);
	while (line == 0) {
	    addr = nextaddr(addr, isnext);
	    line = linelookup(addr);
	}
	curline = line;
    } else {
	curline = 0;
    }
    stepto(addr);
    filename = srcfilename(addr);
    setsource(filename);
}

typedef char Bpinst;

#define BP_OP       O_BPT       /* breakpoint trap */

#define BP_ERRNO    SIGTRAP     /* signal received at a breakpoint */

/*
 * Setting a breakpoint at a location consists of saving
 * the word at the location and poking a BP_OP there.
 *
 * We save the locations and words on a list for use in unsetting.
 */

typedef struct Savelist *Savelist;

struct Savelist {
    Address location;
    Bpinst save;
    short refcount;
    Savelist link;
};

private Savelist savelist;

/*
 * Set a breakpoint at the given address.  Only save the word there
 * if it's not already a breakpoint.
 */

public setbp(addr)
Address addr;
{
    Bpinst w, save;
    register Savelist newsave, s;

    for (s = savelist; s != nil; s = s->link) {
	if (s->location == addr) {
	    s->refcount++;
	    return;
	}
    }
    iread(&save, addr, sizeof(save));
    newsave = new(Savelist);
    newsave->location = addr;
    newsave->save = save;
    newsave->refcount = 1;
    newsave->link = savelist;
    savelist = newsave;
    w = BP_OP;
    iwrite(&w, addr, sizeof(w));
}

/*
 * Unset a breakpoint; unfortunately we have to search the SAVELIST
 * to find the saved value.  The assumption is that the SAVELIST will
 * usually be quite small.
 */

public unsetbp(addr)
Address addr;
{
    register Savelist s, prev;

    prev = nil;
    for (s = savelist; s != nil; s = s->link) {
	if (s->location == addr) {
	    iwrite(&s->save, addr, sizeof(s->save));
	    s->refcount--;
	    if (s->refcount == 0) {
		if (prev == nil) {
		    savelist = s->link;
		} else {
		    prev->link = s->link;
		}
		dispose(s);
	    }
	    return;
	}
	prev = s;
    }
    panic("unsetbp: couldn't find address %d", addr);
}

/*
 * VAX instruction decoder, derived from adb.
 */

private Address printop(addr)
Address addr;
{
    register Optab *op;
    VaxOpcode ins;
    unsigned char mode;
    int argtype, amode, argno, argval;
    String reg;
    Boolean indexf;
    short offset;

    argval = 0;
    indexf = false;
    printf("%08x  ", addr);
    iread(&ins, addr, sizeof(ins));
    addr += 1;
    if (ins == O_ESCF) {
	iread(&ins, addr, sizeof(ins));
	addr += 1;
	op = ioptab[ins];
    } else if (ins == O_ESCD) {
	iread(&ins, addr, sizeof(ins));
	addr += 1;
	op = esctab[ins];
    } else {
	op = ioptab[ins];
    }
    if (op == nil) {
	printf("[unrecognized opcode %#0x]\n", ins);
	return addr;
    }
    printf("%s", op->iname);
    for (argno = 0; argno < op->numargs; argno++) {
	if (indexf == true) {
	    indexf = false;
	} else if (argno == 0) {
	    printf("\t");
	} else {
	    printf(",");
	}
	argtype = op->argtype[argno];
	if (is_branch_disp(argtype)) {
	    mode = 0xAF + (typelen(argtype) << 5);
	} else {
	    iread(&mode, addr, sizeof(mode));
	    addr += 1;
	}
	reg = regname[regnm(mode)];
	amode = addrmode(mode);
	switch (amode) {
	    case LITSHORT:
	    case LITUPTO31:
	    case LITUPTO47:
	    case LITUPTO63:
		if (typelen(argtype) == TYPF || typelen(argtype) == TYPD ||
		    typelen(argtype) == TYPG || typelen(argtype) == TYPH)
		    printf("$%s", fltimm[mode]);
		else
		    printf("$%x", mode);
		argval = mode;
		break;

	    case INDEX:
		printf("[%s]", reg);
		indexf = true;
		argno--;
		break;

	    case REG:
		printf("%s", reg);
		break;

	    case REGDEF:
		printf("(%s)", reg);
		break;

	    case AUTODEC:
		printf("-(%s)", reg);
		break;

	    case AUTOINC:
		if (reg != regname[PROGCTR]) {
		    printf("(%s)+", reg);
		} else {
		    printf("$");
		    switch (typelen(argtype)) {
			case TYPB:
			    argval = printdisp(addr, 1, reg, amode);
			    addr += 1;
			    break;

			case TYPW:
			    argval = printdisp(addr, 2, reg, amode);
			    addr += 2;
			    break;

			case TYPL:
			    argval = printdisp(addr, 4, reg, amode);
			    addr += 4;
			    break;

			case TYPF:
			    iread(&argval, addr, sizeof(argval));
			    if ((argval & 0xffff007f) == 0x8000) {
				printf("[reserved operand]");
			    } else {
				printf("%g", *(float *)&argval);
			    }
			    addr += 4;
			    break;

			case TYPD:
			    /* XXX this bags the low order bits */
			    iread(&argval, addr, sizeof(argval));
			    if ((argval & 0xffff007f) == 0x8000) {
				printf("[reserved operand]");
			    } else {
				printf("%g", *(float *)&argval);
			    }
			    addr += 8;
			    break;

			case TYPG:
			case TYPQ:
			    iread(&argval, addr+4, sizeof(argval));
			    printf("%08x", argval);
			    iread(&argval, addr, sizeof(argval));
			    printf("%08x", argval);
			    addr += 8;
			    break;

			case TYPH:
			case TYPO:
			    iread(&argval, addr+12, sizeof(argval));
			    printf("%08x", argval);
			    iread(&argval, addr+8, sizeof(argval));
			    printf("%08x", argval);
			    iread(&argval, addr+4, sizeof(argval));
			    printf("%08x", argval);
			    iread(&argval, addr, sizeof(argval));
			    printf("%08x", argval);
			    addr += 16;
			    break;
		    }
		}
		break;

	    case AUTOINCDEF:
		if (reg == regname[PROGCTR]) {
		    printf("*$");
		    argval = printdisp(addr, 4, reg, amode);
		    addr += 4;
		} else {
		    printf("*(%s)+", reg);
		}
		break;

	    case BYTEDISP:
		argval = printdisp(addr, 1, reg, amode);
		addr += 1;
		break;

	    case BYTEDISPDEF:
		printf("*");
		argval = printdisp(addr, 1, reg, amode);
		addr += 1;
		break;

	    case WORDDISP:
		argval = printdisp(addr, 2, reg, amode);
		addr += 2;
		break;

	    case WORDDISPDEF:
		printf("*");
		argval = printdisp(addr, 2, reg, amode);
		addr += 2;
		break;

	    case LONGDISP:
		argval = printdisp(addr, 4, reg, amode);
		addr += 4;
		break;

	    case LONGDISPDEF:
		printf("*");
		argval = printdisp(addr, 4, reg, amode);
		addr += 4;
		break;
	}
    }
    if (ins == O_CASEB || ins == O_CASEW || ins == O_CASEL) {
	for (argno = 0; argno <= argval; argno++) {
	    iread(&offset, addr, sizeof(offset));
	    printf("\n\t\t%d", offset);
	    addr += 2;
	}
    }
    printf("\n");
    return addr;
}

/*
 * Print the displacement of an instruction that uses displacement
 * addressing.
 */

private int printdisp(addr, nbytes, reg, mode)
Address addr;
int nbytes;
char *reg;
int mode;
{
    char byte;
    short hword;
    int argval;
    Symbol f;

    switch (nbytes) {
	case 1:
	    iread(&byte, addr, sizeof(byte));
	    argval = byte;
	    break;

	case 2:
	    iread(&hword, addr, sizeof(hword));
	    argval = hword;
	    break;

	case 4:
	    iread(&argval, addr, sizeof(argval));
	    break;
    }
    if (reg == regname[PROGCTR] && mode >= BYTEDISP) {
	argval += addr + nbytes;
    }
    if (reg == regname[PROGCTR]) {
	f = whatblock((Address) argval + 2);
	if (codeloc(f) == argval + 2) {
	    printf("%s", symname(f));
	} else {
	    printf("%x", argval);
	}
    } else {
	if (varIsSet("$hexoffsets")) {
	    if (argval < 0) {
		printf("-%x(%s)", -(argval), reg);
	    } else {
		printf("%x(%s)", argval, reg);
	    }
	} else {
	    printf("%d(%s)", argval, reg);
	}
    }
    return argval;
}

/*
 * Compute the next address that will be executed from the given one.
 * If "isnext" is true then consider a procedure call as straight line code.
 *
 * We must unfortunately do much of the same work that is necessary
 * to print instructions.  In addition we have to deal with branches.
 * Unconditional branches we just follow, for conditional branches
 * we continue execution to the current location and then single step
 * the machine.  We assume that the last argument in an instruction
 * that branches is the branch address (or relative offset).
 */

private Address findnextaddr();

public Address nextaddr(startaddr, isnext)
Address startaddr;
boolean isnext;
{
    Address addr;

    addr = usignal(process);
    if (addr == 0 or addr == 1) {
	addr = findnextaddr(startaddr, isnext);
    }
    return addr;
}

/*
 * Determine if it's ok to skip function f entered by instruction ins.
 * If so, we're going to compute the return address and step to it.
 * Therefore we cannot skip over a function entered by a jsb or bsb,
 * since the return address is not easily computed for them.
 */

private boolean skipfunc (ins, f)
VaxOpcode ins;
Symbol f;
{
    boolean b;

    b = (boolean) (
	ins != O_JSB and ins != O_BSBB and ins != O_BSBW and
	not inst_tracing and nlhdr.nlines != 0 and
	nosource(curfunc) and canskip(curfunc)
    );
    return b;
}

private Address findnextaddr(startaddr, isnext)
Address startaddr;
Boolean isnext;
{
    register Address addr;
    register Optab *op;
    VaxOpcode ins, ins2;
    unsigned char mode;
    int argtype, amode, argno, argval;
    String r;
    Boolean indexf;
    enum { KNOWN, SEQUENTIAL, BRANCH } addrstatus;

    argval = 0;
    indexf = false;
    addr = startaddr;
    iread(&ins, addr, sizeof(ins));
    switch (ins) {
	/*
	 * It used to be that unconditional jumps and branches were handled
	 * by taking their destination address as the next address.  While
	 * saving the cost of starting up the process, this approach
	 * doesn't work when jumping indirect (since the value in the
	 * register might not yet have been set).
	 *
	 * So unconditional jumps and branches are now handled the same way
	 * as conditional jumps and branches.
	 *
	case O_BRB:
	case O_BRW:
	    addrstatus = BRANCH;
	    break;
	 *
	 */

	case O_BSBB:
	case O_BSBW:
	case O_JSB:
	case O_CALLG:
	case O_CALLS:
	    addrstatus = KNOWN;
	    stepto(addr);
	    pstep(process, DEFSIG);
	    addr = reg(PROGCTR);
	    pc = addr;
	    setcurfunc(whatblock(pc));
	    if (not isbperr()) {
		printstatus();
		/* NOTREACHED */
	    }
	    bpact();
	    if (isnext or skipfunc(ins, curfunc)) {
		addrstatus = KNOWN;
		addr = return_addr();
		stepto(addr);
		bpact();
	    } else {
		callnews(/* iscall = */ true);
	    }
	    break;

	case O_RSB:
	case O_RET:
	    addrstatus = KNOWN;
	    stepto(addr);
	    callnews(/* iscall = */ false);
	    pstep(process, DEFSIG);
	    addr = reg(PROGCTR);
	    pc = addr;
	    if (not isbperr()) {
		printstatus();
	    }
	    bpact();
	    break;

	case O_BRB: case O_BRW:
	case O_JMP: /* because it may be jmp (r1) */
	case O_BNEQ: case O_BEQL: case O_BGTR:
	case O_BLEQ: case O_BGEQ: case O_BLSS:
	case O_BGTRU: case O_BLEQU: case O_BVC:
	case O_BVS: case O_BCC: case O_BCS:
	case O_CASEB: case O_CASEW: case O_CASEL:
	case O_BBS: case O_BBC: case O_BBSS: case O_BBCS:
	case O_BBSC: case O_BBCC: case O_BBSSI:
	case O_BBCCI: case O_BLBS: case O_BLBC:
	case O_ACBL: case O_AOBLSS: case O_AOBLEQ:
	case O_SOBGEQ: case O_SOBGTR:
	case O_ESCF: /* bugchecks */
	branches:
	    addrstatus = KNOWN;
	    stepto(addr);
	    pstep(process, DEFSIG);
	    addr = reg(PROGCTR);
	    pc = addr;
	    if (not isbperr()) {
		printstatus();
	    }
	    break;

	case O_ESCD:
	    iread(&ins2, addr+1, sizeof(ins2));
	    if (ins2 == O_ACBF || ins2 == O_ACBD)
		/* actually ACBG and ACBH */
		goto branches;
	    /* fall through */

	default:
	    addrstatus = SEQUENTIAL;
	    break;
    }
    if (addrstatus != KNOWN) {
	addr += 1;
	if (ins == O_ESCD) {
	    ins = ins2;
	    addr += 1;
	    op = esctab[ins];
	    if (op == nil) {
		printf("[bad extended opcode %#x in findnextaddr]\n", ins);
		return addr;
	    }
	} else {
	    op = ioptab[ins];
	    if (op == nil) {
		printf("[bad opcode %#x in findnextaddr]\n", ins);
		return addr;
	    }
	}
	for (argno = 0; argno < op->numargs; argno++) {
	    if (indexf == true) {
		indexf = false;
	    }
	    argtype = op->argtype[argno];
	    if (is_branch_disp(argtype)) {
		mode = 0xAF + (typelen(argtype) << 5);
	    } else {
		iread(&mode, addr, sizeof(mode));
		addr += 1;
	    }
	    r = regname[regnm(mode)];
	    amode = addrmode(mode);
	    switch (amode) {
		case LITSHORT:
		case LITUPTO31:
		case LITUPTO47:
		case LITUPTO63:
		    argval = mode;
		    break;

		case INDEX:
		    indexf = true;
		    --argno;
		    break;

		case REG:
		case REGDEF:
		case AUTODEC:
		    break;

		case AUTOINC:
		    if (r == regname[PROGCTR]) {
			switch (typelen(argtype)) {
			    case TYPB:
				argval = getdisp(addr, 1, r, amode);
				addr += 1;
				break;

			    case TYPW:
				argval = getdisp(addr, 2, r, amode);
				addr += 2;
				break;

			    case TYPL:
				argval = getdisp(addr, 4, r, amode);
				addr += 4;
				break;

			    case TYPF:
				iread(&argval, addr, sizeof(argval));
				addr += 4;
				break;

			    case TYPQ:
			    case TYPD:
			    case TYPG:
				iread(&argval, addr+4, sizeof(argval));
				addr += 8;
				break;

			    case TYPO:
			    case TYPH:
				iread(&argval, addr+12, sizeof(argval));
				addr += 16;
				break;
			}
		    }
		    break;

		case AUTOINCDEF:
		    if (r == regname[PROGCTR]) {
			argval = getdisp(addr, 4, r, amode);
			addr += 4;
		    }
		    break;

		case BYTEDISP:
		case BYTEDISPDEF:
		    argval = getdisp(addr, 1, r, amode);
		    addr += 1;
		    break;

		case WORDDISP:
		case WORDDISPDEF:
		    argval = getdisp(addr, 2, r, amode);
		    addr += 2;
		    break;

		case LONGDISP:
		case LONGDISPDEF:
		    argval = getdisp(addr, 4, r, amode);
		    addr += 4;
		    break;
	    }
	}
	if (ins == O_CALLS or ins == O_CALLG) {
	    argval += 2;
	}
	if (addrstatus == BRANCH) {
	    addr = argval;
	}
    }
    return addr;
}

/*
 * Get the displacement of an instruction that uses displacement addressing.
 */

private int getdisp(addr, nbytes, reg, mode)
Address addr;
int nbytes;
String reg;
int mode;
{
    char byte;
    short hword;
    int argval;

    switch (nbytes) {
	case 1:
	    iread(&byte, addr, sizeof(byte));
	    argval = byte;
	    break;

	case 2:
	    iread(&hword, addr, sizeof(hword));
	    argval = hword;
	    break;

	case 4:
	    iread(&argval, addr, sizeof(argval));
	    break;
    }
    if (reg == regname[PROGCTR] && mode >= BYTEDISP) {
	argval += addr + nbytes;
    }
    return argval;
}

/*
 * Enter a procedure by creating and executing a call instruction.
 */

#define CALLSIZE 7	/* size of call instruction */

public beginproc(p, argc)
Symbol p;
Integer argc;
{
    char save[CALLSIZE];
    struct {
	VaxOpcode op;
	unsigned char numargs;
	unsigned char mode;
	char addr[sizeof(long)];	/* unaligned long */
    } call;
    long dest;

    pc = 2;
    iread(save, pc, sizeof(save));
    call.op = O_CALLS;
    call.numargs = argc;
    call.mode = 0xef;
    dest = codeloc(p) - 2 - (pc + 7);
    mov(&dest, call.addr, sizeof(call.addr));
    iwrite(&call, pc, sizeof(call));
    setreg(PROGCTR, pc);
    pstep(process, DEFSIG);
    iwrite(save, pc, sizeof(save));
    pc = reg(PROGCTR);
    if (not isbperr()) {
	printstatus();
    }
}

/*
 * Special variables for debugging the kernel.
 */

public integer masterpcbb;
public integer slr;
public struct pte *sbr;
private struct pcb pcb;

public getpcb ()
{
    integer i;

    fseek(corefile, masterpcbb & ~0x80000000, 0);
    get(corefile, pcb);
    pcb.pcb_p0lr &= ~AST_CLR;
    printf("p0br %lx p0lr %lx p1br %lx p1lr %lx\n",
	pcb.pcb_p0br, pcb.pcb_p0lr, pcb.pcb_p1br, pcb.pcb_p1lr
    );
    setreg(0, pcb.pcb_r0);
    setreg(1, pcb.pcb_r1);
    setreg(2, pcb.pcb_r2);
    setreg(3, pcb.pcb_r3);
    setreg(4, pcb.pcb_r4);
    setreg(5, pcb.pcb_r5);
    setreg(6, pcb.pcb_r6);
    setreg(7, pcb.pcb_r7);
    setreg(8, pcb.pcb_r8);
    setreg(9, pcb.pcb_r9);
    setreg(10, pcb.pcb_r10);
    setreg(11, pcb.pcb_r11);
    setreg(ARGP, pcb.pcb_ap);
    setreg(FRP, pcb.pcb_fp);
    setreg(STKP, pcb.pcb_ksp);
    setreg(PROGCTR, pcb.pcb_pc);
}

public copyregs (savreg, reg)
Word savreg[], reg[];
{
    reg[0] = savreg[R0];
    reg[1] = savreg[R1];
    reg[2] = savreg[R2];
    reg[3] = savreg[R3];
    reg[4] = savreg[R4];
    reg[5] = savreg[R5];
    reg[6] = savreg[R6];
    reg[7] = savreg[R7];
    reg[8] = savreg[R8];
    reg[9] = savreg[R9];
    reg[10] = savreg[R10];
    reg[11] = savreg[R11];
    reg[ARGP] = savreg[AP];
    reg[FRP] = savreg[FP];
    reg[STKP] = savreg[SP];
    reg[PROGCTR] = savreg[PC];
}

/*
 * Map a virtual address to a physical address.
 */

public Address vmap (addr)
Address addr;
{
    Address r;
    integer v, n;
    struct pte pte;

    r = addr & ~0xc0000000;
    v = btop(r);
    switch (addr&0xc0000000) {
	case 0xc0000000:
	case 0x80000000:
	    /*
	     * In system space, so get system pte.
	     * If it is valid or reclaimable then the physical address
	     * is the combination of its page number and the page offset
	     * of the original address.
	     */
	    if (v >= slr) {
		error("address %x out of segment", addr);
	    }
	    r = ((long) (sbr + v)) & ~0x80000000;
	    goto simple;

	case 0x40000000:
	    /*
	     * In p1 space, must not be in shadow region.
	     */
	    if (v < pcb.pcb_p1lr) {
		error("address %x out of segment", addr);
	    }
	    r = (Address) (pcb.pcb_p1br + v);
	    break;

	case 0x00000000:
	    /*
	     * In p0 space, must not be off end of region.
	     */
	    if (v >= pcb.pcb_p0lr) {
		error("address %x out of segment", addr);
	    }
	    r = (Address) (pcb.pcb_p0br + v);
	    break;

	default:
	    /* do nothing */
	    break;
    }
    /*
     * For p0/p1 address, user-level page table should be in
     * kernel virtual memory.  Do second-level indirect by recursing.
     */
    if ((r & 0x80000000) == 0) {
	error("bad p0br or p1br in pcb");
    }
    r = vmap(r);
simple:
    /*
     * "r" is now the address of the pte of the page
     * we are interested in; get the pte and paste up the physical address.
     */
    fseek(corefile, r, 0);
    n = fread(&pte, sizeof(pte), 1, corefile);
    if (n != 1) {
	error("page table botch (fread at %x returns %d)", r, n);
    }
    if (pte.pg_v == 0 and (pte.pg_fod != 0 or pte.pg_pfnum == 0)) {
	error("page no valid or reclamable");
    }
    return (addr&PGOFSET) + ((Address) ptob(pte.pg_pfnum));
}

/*
 * Extract a bit field from an integer.
 */

public integer extractField (s)
Symbol s;
{
    integer n, nbytes, r;

    n = 0;
    nbytes = size(s);
    if (nbytes > sizeof(n)) {
	printf("[bad size in extractField -- word assumed]\n");
	nbytes = sizeof(n);
    }
    popn(nbytes, &n);
    r = n >> (s->symvalue.field.offset mod BITSPERBYTE);
    r &= ((1 << s->symvalue.field.length) - 1);
    return r;
}

/*
 * Change the length of a value in memory according to a given difference
 * in the lengths of its new and old types.
 */

public loophole (oldlen, newlen)
integer oldlen, newlen;
{
    integer n, i;

    n = newlen - oldlen;
    if (n > 0) {
	for (i = 0; i < n; i++) {
	    sp[i] = '\0';
	}
    }
    sp += n;
}