span.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

			goto aconsize;

		case D_PARAM:
			instoffset = autosize + a->offset + 4L;
		aconsize:
			t = immrot(instoffset);
			if(t)
				return C_RACON;
			return C_LACON;
		}
		return C_GOK;

	case D_BRANCH:
		return C_SBRA;
	}
	return C_GOK;
}

Optab*
oplook(Prog *p)
{
	int a1, a2, a3, r;
	char *c1, *c3;
	Optab *o, *e;

	a1 = p->optab;
	if(a1)
		return optab+(a1-1);
	a1 = p->from.class;
	if(a1 == 0) {
		a1 = aclass(&p->from) + 1;
		p->from.class = a1;
	}
	a1--;
	a3 = p->to.class;
	if(a3 == 0) {
		a3 = aclass(&p->to) + 1;
		p->to.class = a3;
	}
	a3--;
	a2 = C_NONE;
	if(p->reg != NREG)
		a2 = C_REG;
	r = p->as;
	o = oprange[r].start;
	if(o == 0) {
		a1 = opcross[repop[r]][a1][a2][a3];
		if(a1) {
			p->optab = a1+1;
			return optab+a1;
		}
		o = oprange[r].stop; /* just generate an error */
	}
	if(0) {
		print("oplook %A %d %d %d\n",
			(int)p->as, a1, a2, a3);
		print("		%d %d\n", p->from.type, p->to.type);
	}
	e = oprange[r].stop;
	c1 = xcmp[a1];
	c3 = xcmp[a3];
	for(; o<e; o++)
		if(o->a2 == a2)
		if(c1[o->a1])
		if(c3[o->a3]) {
			p->optab = (o-optab)+1;
			return o;
		}
	diag("illegal combination %A %d %d %d",
		p->as, a1, a2, a3);
	prasm(p);
	if(o == 0)
		o = optab;
	return o;
}

int
cmp(int a, int b)
{

	if(a == b)
		return 1;
	switch(a) {
	case C_LCON:
		if(b == C_RCON || b == C_NCON)
			return 1;
		break;
	case C_LACON:
		if(b == C_RACON)
			return 1;
		break;
	case C_LECON:
		if(b == C_RECON)
			return 1;
		break;

	case C_HFEXT:
		return b == C_HEXT || b == C_FEXT;
	case C_FEXT:
	case C_HEXT:
		return b == C_HFEXT;
	case C_SEXT:
		return cmp(C_HFEXT, b);
	case C_LEXT:
		return cmp(C_SEXT, b);

	case C_HFAUTO:
		return b == C_HAUTO || b == C_FAUTO;
	case C_FAUTO:
	case C_HAUTO:
		return b == C_HFAUTO;
	case C_SAUTO:
		return cmp(C_HFAUTO, b);
	case C_LAUTO:
		return cmp(C_SAUTO, b);

	case C_HFOREG:
		return b == C_HOREG || b == C_FOREG;
	case C_FOREG:
	case C_HOREG:
		return b == C_HFOREG;
	case C_SROREG:
		return cmp(C_SOREG, b) || cmp(C_ROREG, b);
	case C_SOREG:
	case C_ROREG:
		return b == C_SROREG || cmp(C_HFOREG, b);
	case C_LOREG:
		return cmp(C_SROREG, b);

	case C_LBRA:
		if(b == C_SBRA)
			return 1;
		break;
	}
	return 0;
}

int
ocmp(const void *a1, const void *a2)
{
	Optab *p1, *p2;
	int n;

	p1 = (Optab*)a1;
	p2 = (Optab*)a2;
	n = p1->as - p2->as;
	if(n)
		return n;
	n = (p2->flag&V4) - (p1->flag&V4);	/* architecture version */
	if(n)
		return n;
	n = p1->a1 - p2->a1;
	if(n)
		return n;
	n = p1->a2 - p2->a2;
	if(n)
		return n;
	n = p1->a3 - p2->a3;
	if(n)
		return n;
	return 0;
}

void
buildop(void)
{
	int i, n, r;

	armv4 = !debug['h'];
	for(i=0; i<C_GOK; i++)
		for(n=0; n<C_GOK; n++)
			xcmp[i][n] = cmp(n, i);
	for(n=0; optab[n].as != AXXX; n++)
		if((optab[n].flag & V4) && !armv4) {
			optab[n].as = AXXX;
			break;
		}
	qsort(optab, n, sizeof(optab[0]), ocmp);
	for(i=0; i<n; i++) {
		r = optab[i].as;
		oprange[r].start = optab+i;
		while(optab[i].as == r)
			i++;
		oprange[r].stop = optab+i;
		i--;

		switch(r)
		{
		default:
			diag("unknown op in build: %A", r);
			errorexit();
		case AADD:
			oprange[AAND] = oprange[r];
			oprange[AEOR] = oprange[r];
			oprange[ASUB] = oprange[r];
			oprange[ARSB] = oprange[r];
			oprange[AADC] = oprange[r];
			oprange[ASBC] = oprange[r];
			oprange[ARSC] = oprange[r];
			oprange[AORR] = oprange[r];
			oprange[ABIC] = oprange[r];
			break;
		case ACMP:
			oprange[ATST] = oprange[r];
			oprange[ATEQ] = oprange[r];
			oprange[ACMN] = oprange[r];
			break;
		case AMVN:
			break;
		case ABEQ:
			oprange[ABNE] = oprange[r];
			oprange[ABCS] = oprange[r];
			oprange[ABHS] = oprange[r];
			oprange[ABCC] = oprange[r];
			oprange[ABLO] = oprange[r];
			oprange[ABMI] = oprange[r];
			oprange[ABPL] = oprange[r];
			oprange[ABVS] = oprange[r];
			oprange[ABVC] = oprange[r];
			oprange[ABHI] = oprange[r];
			oprange[ABLS] = oprange[r];
			oprange[ABGE] = oprange[r];
			oprange[ABLT] = oprange[r];
			oprange[ABGT] = oprange[r];
			oprange[ABLE] = oprange[r];
			break;
		case ASLL:
			oprange[ASRL] = oprange[r];
			oprange[ASRA] = oprange[r];
			break;
		case AMUL:
			oprange[AMULU] = oprange[r];
			break;
		case ADIV:
			oprange[AMOD] = oprange[r];
			oprange[AMODU] = oprange[r];
			oprange[ADIVU] = oprange[r];
			break;
		case AMOVW:
		case AMOVB:
		case AMOVBU:
		case AMOVH:
		case AMOVHU:
			break;
		case ASWPW:
			oprange[ASWPBU] = oprange[r];
			break;
		case AB:
		case ABL:
		case ABX:
		case ABXRET:
		case ASWI:
		case AWORD:
		case AMOVM:
		case ARFE:
		case ATEXT:
		case ACASE:
		case ABCASE:
			break;
		case AADDF:
			oprange[AADDD] = oprange[r];
			oprange[ASUBF] = oprange[r];
			oprange[ASUBD] = oprange[r];
			oprange[AMULF] = oprange[r];
			oprange[AMULD] = oprange[r];
			oprange[ADIVF] = oprange[r];
			oprange[ADIVD] = oprange[r];
			oprange[AMOVFD] = oprange[r];
			oprange[AMOVDF] = oprange[r];
			break;
			
		case ACMPF:
			oprange[ACMPD] = oprange[r];
			break;

		case AMOVF:
			oprange[AMOVD] = oprange[r];
			break;

		case AMOVFW:
			oprange[AMOVWF] = oprange[r];
			oprange[AMOVWD] = oprange[r];
			oprange[AMOVDW] = oprange[r];
			break;

		case AMULL:
			oprange[AMULA] = oprange[r];
			oprange[AMULAL] = oprange[r];
			oprange[AMULLU] = oprange[r];
			oprange[AMULALU] = oprange[r];
			break;
		}
	}
}

/*
void
buildrep(int x, int as)
{
	Opcross *p;
	Optab *e, *s, *o;
	int a1, a2, a3, n;

	if(C_NONE != 0 || C_REG != 1 || C_GOK >= 32 || x >= nelem(opcross)) {
		diag("assumptions fail in buildrep");
		errorexit();
	}
	repop[as] = x;
	p = (opcross + x);
	s = oprange[as].start;
	e = oprange[as].stop;
	for(o=e-1; o>=s; o--) {
		n = o-optab;
		for(a2=0; a2<2; a2++) {
			if(a2) {
				if(o->a2 == C_NONE)
					continue;
			} else
				if(o->a2 != C_NONE)
					continue;
			for(a1=0; a1<32; a1++) {
				if(!xcmp[a1][o->a1])
					continue;
				for(a3=0; a3<32; a3++)
					if(xcmp[a3][o->a3])
						(*p)[a1][a2][a3] = n;
			}
		}
	}
	oprange[as].start = 0;
}
*/

enum{
	ABSD = 0,
	ABSU = 1,
	RELD = 2,
	RELU = 3,
};

int modemap[4] = { 0, 1, -1, 2, };

typedef struct Reloc Reloc;

struct Reloc
{
	int n;
	int t;
	uchar *m;
	ulong *a;
};

Reloc rels;

static void
grow(Reloc *r)
{
	int t;
	uchar *m, *nm;
	ulong *a, *na;

	t = r->t;
	r->t += 64;
	m = r->m;
	a = r->a;
	r->m = nm = malloc(r->t*sizeof(uchar));
	r->a = na = malloc(r->t*sizeof(ulong));
	memmove(nm, m, t*sizeof(uchar));
	memmove(na, a, t*sizeof(ulong));
	free(m);
	free(a);
}

void
dynreloc(Sym *s, long v, int abs)
{
	int i, k, n;
	uchar *m;
	ulong *a;
	Reloc *r;

	if(v&3)
		diag("bad relocation address");
	v >>= 2;
	if(s != S && s->type == SUNDEF)
		k = abs ? ABSU : RELU;
	else
		k = abs ? ABSD : RELD;
	/* Bprint(&bso, "R %s a=%ld(%lx) %d\n", s->name, a, a, k); */
	k = modemap[k];
	r = &rels;
	n = r->n;
	if(n >= r->t)
		grow(r);
	m = r->m;
	a = r->a;
	for(i = n; i > 0; i--){
		if(v < a[i-1]){	/* happens occasionally for data */
			m[i] = m[i-1];
			a[i] = a[i-1];
		}
		else
			break;
	}
	m[i] = k;
	a[i] = v;
	r->n++;
}

static int
sput(char *s)
{
	char *p;

	p = s;
	while(*s)
		cput(*s++);
	cput(0);
	return  s-p+1;
}

void
asmdyn()
{
	int i, n, t, c;
	Sym *s;
	ulong la, ra, *a;
	vlong off;
	uchar *m;
	Reloc *r;

	cflush();
	off = seek(cout, 0, 1);
	lput(0);
	t = 0;
	lput(imports);
	t += 4;
	for(i = 0; i < NHASH; i++)
		for(s = hash[i]; s != S; s = s->link)
			if(s->type == SUNDEF){
				lput(s->sig);
				t += 4;
				t += sput(s->name);
			}
	
	la = 0;
	r = &rels;
	n = r->n;
	m = r->m;
	a = r->a;
	lput(n);
	t += 4;
	for(i = 0; i < n; i++){
		ra = *a-la;
		if(*a < la)
			diag("bad relocation order");
		if(ra < 256)
			c = 0;
		else if(ra < 65536)
			c = 1;
		else
			c = 2;
		cput((c<<6)|*m++);
		t++;
		if(c == 0){
			cput(ra);
			t++;
		}
		else if(c == 1){
			wput(ra);
			t += 2;
		}
		else{
			lput(ra);
			t += 4;
		}
		la = *a++;
	}

	cflush();
	seek(cout, off, 0);
	lput(t);

	if(debug['v']){
		Bprint(&bso, "import table entries = %d\n", imports);
		Bprint(&bso, "export table entries = %d\n", exports);
	}
}