obj.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

/*
 * obj.c
 * routines universal to all object files
 */
#include <u.h>
#include <libc.h>
#include <bio.h>
#include <ar.h>
#include <mach.h>
#include "obj.h"

#define islocal(t)	((t)=='a' || (t)=='p')

enum
{
	NNAMES	= 50,
	MAXIS	= 8,		/* max length to determine if a file is a .? file */
	MAXOFF	= 0x7fffffff,	/* larger than any possible local offset */
	NHASH	= 1024,		/* must be power of two */
	HASHMUL	= 79L,
};

int	_is2(char*),		/* in [$OS].c */
	_is5(char*),
	_is6(char*),
	_is7(char*),
	_is8(char*),
	_isk(char*),
	_isq(char*),
	_isv(char*),
	_isu(char*),
	_read2(Biobuf*, Prog*),
	_read5(Biobuf*, Prog*),
	_read6(Biobuf*, Prog*),
	_read7(Biobuf*, Prog*),
	_read8(Biobuf*, Prog*),
	_readk(Biobuf*, Prog*),
	_readq(Biobuf*, Prog*),
	_readv(Biobuf*, Prog*),
	_readu(Biobuf*, Prog*);

typedef struct Obj	Obj;
typedef struct Symtab	Symtab;

struct	Obj		/* functions to handle each intermediate (.$O) file */
{
	char	*name;				/* name of each $O file */
	int	(*is)(char*);			/* test for each type of $O file */
	int	(*read)(Biobuf*, Prog*);	/* read for each type of $O file*/
};

static Obj	obj[] =
{			/* functions to identify and parse each type of obj */
	[Obj68020]	"68020 .2",	_is2, _read2,
	[ObjAmd64]	"amd64 .6",	_is6, _read6,
	[ObjArm]	"arm .5",	_is5, _read5,
	[ObjAlpha]	"alpha .7",	_is7, _read7,
	[Obj386]	"386 .8",	_is8, _read8,
	[ObjSparc]	"sparc .k",	_isk, _readk,
	[ObjPower]	"power .q",	_isq, _readq,
	[ObjMips]	"mips .v",	_isv, _readv,
	[ObjSparc64]	"sparc64 .u",	_isu, _readu,
	[Maxobjtype]	0, 0
};

struct	Symtab
{
	struct	Sym 	s;
	struct	Symtab	*next;
};

static	Symtab *hash[NHASH];
static	Sym	*names[NNAMES];	/* working set of active names */

static	int	processprog(Prog*,int);	/* decode each symbol reference */
static	void	objreset(void);
static	void	objlookup(int, char *, int, uint);
static	void 	objupdate(int, int);

int
objtype(Biobuf *bp, char **name)
{
	int i;
	char buf[MAXIS];

	if(Bread(bp, buf, MAXIS) < MAXIS)
		return -1;
	Bseek(bp, -MAXIS, 1);
	for (i = 0; i < Maxobjtype; i++) {
		if (obj[i].is && (*obj[i].is)(buf)) {
			if (name)
				*name = obj[i].name;
			return i;
		}
	}
	return -1;
}

int
isar(Biobuf *bp)
{
	int n;
	char magbuf[SARMAG];

	n = Bread(bp, magbuf, SARMAG);
	if(n == SARMAG && strncmp(magbuf, ARMAG, SARMAG) == 0)
		return 1;
	return 0;
}

/*
 * determine what kind of object file this is and process it.
 * return whether or not this was a recognized intermediate file.
 */
int
readobj(Biobuf *bp, int objtype)
{
	Prog p;

	if (objtype < 0 || objtype >= Maxobjtype || obj[objtype].is == 0)
		return 1;
	objreset();
	while ((*obj[objtype].read)(bp, &p))
		if (!processprog(&p, 1))
			return 0;
	return 1;
}

int
readar(Biobuf *bp, int objtype, vlong end, int doautos)
{
	Prog p;

	if (objtype < 0 || objtype >= Maxobjtype || obj[objtype].is == 0)
		return 1;
	objreset();
	while ((*obj[objtype].read)(bp, &p) && Boffset(bp) < end)
		if (!processprog(&p, doautos))
			return 0;
	return 1;
}

/*
 *	decode a symbol reference or definition
 */
static	int
processprog(Prog *p, int doautos)
{
	if(p->kind == aNone)
		return 1;
	if(p->sym < 0 || p->sym >= NNAMES)
		return 0;
	switch(p->kind)
	{
	case aName:
		if (!doautos)
		if(p->type != 'U' && p->type != 'b')
			break;
		objlookup(p->sym, p->id, p->type, p->sig);
		break;
	case aText:
		objupdate(p->sym, 'T');
		break;
	case aData:
		objupdate(p->sym, 'D');
		break;
	default:
		break;
	}
	return 1;
}

/*
 * find the entry for s in the symbol array.
 * make a new entry if it is not already there.
 */
static void
objlookup(int id, char *name, int type, uint sig)
{
	long h;
	char *cp;
	Sym *s;
	Symtab *sp;

	s = names[id];
	if(s && strcmp(s->name, name) == 0) {
		s->type = type;
		s->sig = sig;
		return;
	}

	h = *name;
	for(cp = name+1; *cp; h += *cp++)
		h *= HASHMUL;
	if(h < 0)
		h = ~h;
	h &= (NHASH-1);
	if (type == 'U' || type == 'b' || islocal(type)) {
		for(sp = hash[h]; sp; sp = sp->next)
			if(strcmp(sp->s.name, name) == 0) {
				switch(sp->s.type) {
				case 'T':
				case 'D':
				case 'U':
					if (type == 'U') {
						names[id] = &sp->s;
						return;
					}
					break;
				case 't':
				case 'd':
				case 'b':
					if (type == 'b') {
						names[id] = &sp->s;
						return;
					}
					break;
				case 'a':
				case 'p':
					if (islocal(type)) {
						names[id] = &sp->s;
						return;
					}
					break;
				default:
					break;
				}
			}
	}
	sp = malloc(sizeof(Symtab));
	sp->s.name = name;
	sp->s.type = type;
	sp->s.sig = sig;
	sp->s.value = islocal(type) ? MAXOFF : 0;
	names[id] = &sp->s;
	sp->next = hash[h];
	hash[h] = sp;
	return;
}
/*
 *	traverse the symbol lists
 */
void
objtraverse(void (*fn)(Sym*, void*), void *pointer)
{
	int i;
	Symtab *s;

	for(i = 0; i < NHASH; i++)
		for(s = hash[i]; s; s = s->next)
			(*fn)(&s->s, pointer);
}

/*
 * update the offset information for a 'a' or 'p' symbol in an intermediate file
 */
void
_offset(int id, vlong off)
{
	Sym *s;

	s = names[id];
	if (s && s->name[0] && islocal(s->type) && s->value > off)
		s->value = off;
}

/*
 * update the type of a global text or data symbol
 */
static void 
objupdate(int id, int type)
{
	Sym *s;

	s = names[id];
	if (s && s->name[0])
		if (s->type == 'U')
			s->type = type;
		else if (s->type == 'b')
			s->type = tolower(type);
}

/*
 * look for the next file in an archive
 */
int
nextar(Biobuf *bp, int offset, char *buf)
{
	struct ar_hdr a;
	int i, r;
	long arsize;

	if (offset&01)
		offset++;
	Bseek(bp, offset, 0);
	r = Bread(bp, &a, SAR_HDR);
	if(r != SAR_HDR)
		return 0;
	if(strncmp(a.fmag, ARFMAG, sizeof(a.fmag)))
		return -1;
	for(i=0; i<sizeof(a.name) && i<SARNAME && a.name[i] != ' '; i++)
		buf[i] = a.name[i];
	buf[i] = 0;
	arsize = strtol(a.size, 0, 0);
	if (arsize&1)
		arsize++;
	return arsize + SAR_HDR;
}

static void
objreset(void)
{
	int i;
	Symtab *s, *n;

	for(i = 0; i < NHASH; i++) {
		for(s = hash[i]; s; s = n) {
			n = s->next;
			free(s->s.name);
			free(s);
		}
		hash[i] = 0;
	}
	memset(names, 0, sizeof names);
}