executable.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

		fp->dataddr = _round(fp->txtaddr+fp->txtsz, mach->pgsize);
		break;
	case FARM:
		fp->txtaddr = mach->kbase+0x8010;
		fp->name = "ARM plan 9 boot image";
		fp->dataddr = fp->txtaddr+fp->txtsz;
		return;
	case FALPHA:
		fp->type = FALPHAB;
		fp->txtaddr = (u32int)fp->entry;
		fp->name = "alpha plan 9 boot image";
		fp->dataddr = fp->txtaddr+fp->txtsz;
		break;
	case FPOWER:
		fp->type = FPOWERB;
		fp->txtaddr = (u32int)fp->entry;
		fp->name = "power plan 9 boot image";
		fp->dataddr = fp->txtaddr+fp->txtsz;
		break;
	case FAMD64:
		fp->type = FAMD64B;
		fp->txtaddr = fp->entry;
		fp->name = "amd64 plan 9 boot image";
		fp->dataddr = _round(fp->txtaddr+fp->txtsz, mach->pgsize);
		break;
	default:
		return;
	}
	fp->hdrsz = 0;			/* header stripped */
}

/*
 *	_MAGIC() style headers and
 *	alpha plan9-style bootable images for axp "headerless" boot
 *
 */
static int
common(int fd, Fhdr *fp, ExecHdr *hp)
{
	adotout(fd, fp, hp);
	if(hp->e.magic & DYN_MAGIC) {
		fp->txtaddr = 0;
		fp->dataddr = fp->txtsz;
		return 1;
	}
	commonboot(fp);
	return 1;
}

static int
commonllp64(int, Fhdr *fp, ExecHdr *hp)
{
	long pgsize;
	uvlong entry;

	hswal(&hp->e, sizeof(Exec)/sizeof(long), beswal);
	if(!(hp->e.magic & HDR_MAGIC))
		return 0;

	/*
	 * There can be more magic here if the
	 * header ever needs more expansion.
	 * For now just catch use of any of the
	 * unused bits.
	 */
	if((hp->e.magic & ~DYN_MAGIC)>>16)
		return 0;
	entry = beswav(hp->e.hdr[0]);

	pgsize = mach->pgsize;
	settext(fp, entry, pgsize+fp->hdrsz, hp->e.text, fp->hdrsz);
	setdata(fp, _round(pgsize+fp->txtsz+fp->hdrsz, pgsize),
		hp->e.data, fp->txtsz+fp->hdrsz, hp->e.bss);
	setsym(fp, hp->e.syms, hp->e.spsz, hp->e.pcsz, fp->datoff+fp->datsz);

	if(hp->e.magic & DYN_MAGIC) {
		fp->txtaddr = 0;
		fp->dataddr = fp->txtsz;
		return 1;
	}
	commonboot(fp);
	return 1;
}

/*
 *	mips bootable image.
 */
static int
mipsboot(int fd, Fhdr *fp, ExecHdr *hp)
{
	USED(fd);
	fp->type = FMIPSB;
	switch(hp->e.amagic) {
	default:
	case 0407:	/* some kind of mips */
		settext(fp, (u32int)hp->e.mentry, (u32int)hp->e.text_start,
			hp->e.tsize, sizeof(struct mipsexec)+4);
		setdata(fp, (u32int)hp->e.data_start, hp->e.dsize,
			fp->txtoff+hp->e.tsize, hp->e.bsize);
		break;
	case 0413:	/* some kind of mips */
		settext(fp, (u32int)hp->e.mentry, (u32int)hp->e.text_start,
			hp->e.tsize, 0);
		setdata(fp, (u32int)hp->e.data_start, hp->e.dsize,
			hp->e.tsize, hp->e.bsize);
		break;
	}
	setsym(fp, hp->e.nsyms, 0, hp->e.pcsize, hp->e.symptr);
	fp->hdrsz = 0;			/* header stripped */
	return 1;
}

/*
 *	mips4k bootable image.
 */
static int
mips4kboot(int fd, Fhdr *fp, ExecHdr *hp)
{
	USED(fd);
	fp->type = FMIPSB;
	switch(hp->e.h.amagic) {
	default:
	case 0407:	/* some kind of mips */
		settext(fp, (u32int)hp->e.h.mentry, (u32int)hp->e.h.text_start,
			hp->e.h.tsize, sizeof(struct mips4kexec));
		setdata(fp, (u32int)hp->e.h.data_start, hp->e.h.dsize,
			fp->txtoff+hp->e.h.tsize, hp->e.h.bsize);
		break;
	case 0413:	/* some kind of mips */
		settext(fp, (u32int)hp->e.h.mentry, (u32int)hp->e.h.text_start,
			hp->e.h.tsize, 0);
		setdata(fp, (u32int)hp->e.h.data_start, hp->e.h.dsize,
			hp->e.h.tsize, hp->e.h.bsize);
		break;
	}
	setsym(fp, hp->e.h.nsyms, 0, hp->e.h.pcsize, hp->e.h.symptr);
	fp->hdrsz = 0;			/* header stripped */
	return 1;
}

/*
 *	sparc bootable image
 */
static int
sparcboot(int fd, Fhdr *fp, ExecHdr *hp)
{
	USED(fd);
	fp->type = FSPARCB;
	settext(fp, hp->e.sentry, hp->e.sentry, hp->e.stext,
		sizeof(struct sparcexec));
	setdata(fp, hp->e.sentry+hp->e.stext, hp->e.sdata,
		fp->txtoff+hp->e.stext, hp->e.sbss);
	setsym(fp, hp->e.ssyms, 0, hp->e.sdrsize, fp->datoff+hp->e.sdata);
	fp->hdrsz = 0;			/* header stripped */
	return 1;
}

/*
 *	next bootable image
 */
static int
nextboot(int fd, Fhdr *fp, ExecHdr *hp)
{
	USED(fd);
	fp->type = FNEXTB;
	settext(fp, hp->e.textc.vmaddr, hp->e.textc.vmaddr,
		hp->e.texts.size, hp->e.texts.offset);
	setdata(fp, hp->e.datac.vmaddr, hp->e.datas.size,
		hp->e.datas.offset, hp->e.bsss.size);
	setsym(fp, hp->e.symc.nsyms, hp->e.symc.spoff, hp->e.symc.pcoff,
		hp->e.symc.symoff);
	fp->hdrsz = 0;			/* header stripped */
	return 1;
}

/*
 * Elf32 binaries.
 */
static int
elfdotout(int fd, Fhdr *fp, ExecHdr *hp)
{

	ulong (*swal)(ulong);
	ushort (*swab)(ushort);
	Ehdr *ep;
	Phdr *ph;
	int i, it, id, is, phsz;

	/* bitswap the header according to the DATA format */
	ep = &hp->e;
	if(ep->ident[CLASS] != ELFCLASS32) {
		werrstr("bad ELF class - not 32 bit");
		return 0;
	}
	if(ep->ident[DATA] == ELFDATA2LSB) {
		swab = leswab;
		swal = leswal;
	} else if(ep->ident[DATA] == ELFDATA2MSB) {
		swab = beswab;
		swal = beswal;
	} else {
		werrstr("bad ELF encoding - not big or little endian");
		return 0;
	}

	ep->type = swab(ep->type);
	ep->machine = swab(ep->machine);
	ep->version = swal(ep->version);
	ep->elfentry = swal(ep->elfentry);
	ep->phoff = swal(ep->phoff);
	ep->shoff = swal(ep->shoff);
	ep->flags = swal(ep->flags);
	ep->ehsize = swab(ep->ehsize);
	ep->phentsize = swab(ep->phentsize);
	ep->phnum = swab(ep->phnum);
	ep->shentsize = swab(ep->shentsize);
	ep->shnum = swab(ep->shnum);
	ep->shstrndx = swab(ep->shstrndx);
	if(ep->type != EXEC || ep->version != CURRENT)
		return 0;

	/* we could definitely support a lot more machines here */
	fp->magic = ELF_MAG;
	fp->hdrsz = (ep->ehsize+ep->phnum*ep->phentsize+16)&~15;
	switch(ep->machine) {
	case I386:
		mach = &mi386;
		fp->type = FI386;
		break;
	case MIPS:
		mach = &mmips;
		fp->type = FMIPS;
		break;
	case SPARC64:
		mach = &msparc64;
		fp->type = FSPARC64;
		break;
	case POWER:
		mach = &mpower;
		fp->type = FPOWER;
		break;
	case AMD64:
		mach = &mamd64;
		fp->type = FAMD64;
		break;
	default:
		return 0;
	}

	if(ep->phentsize != sizeof(Phdr)) {
		werrstr("bad ELF header size");
		return 0;
	}
	phsz = sizeof(Phdr)*ep->phnum;
	ph = malloc(phsz);
	if(!ph)
		return 0;
	seek(fd, ep->phoff, 0);
	if(read(fd, ph, phsz) < 0) {
		free(ph);
		return 0;
	}
	hswal(ph, phsz/sizeof(ulong), swal);

	/* find text, data and symbols and install them */
	it = id = is = -1;
	for(i = 0; i < ep->phnum; i++) {
		if(ph[i].type == LOAD
		&& (ph[i].flags & (R|X)) == (R|X) && it == -1)
			it = i;
		else if(ph[i].type == LOAD
		&& (ph[i].flags & (R|W)) == (R|W) && id == -1)
			id = i;
		else if(ph[i].type == NOPTYPE && is == -1)
			is = i;
	}
	if(it == -1 || id == -1) {
		/*
		 * The SPARC64 boot image is something of an ELF hack.
		 * Text+Data+BSS are represented by ph[0].  Symbols
		 * are represented by ph[1]:
		 *
		 *		filesz, memsz, vaddr, paddr, off
		 * ph[0] : txtsz+datsz, txtsz+datsz+bsssz, txtaddr-KZERO, datasize, txtoff
		 * ph[1] : symsz, lcsz, 0, 0, symoff
		 */
		if(ep->machine == SPARC64 && ep->phnum == 2) {
			ulong txtaddr, txtsz, dataddr, bsssz;

			txtaddr = ph[0].vaddr | 0x80000000;
			txtsz = ph[0].filesz - ph[0].paddr;
			dataddr = txtaddr + txtsz;
			bsssz = ph[0].memsz - ph[0].filesz;
			settext(fp, ep->elfentry | 0x80000000, txtaddr, txtsz, ph[0].offset);
			setdata(fp, dataddr, ph[0].paddr, ph[0].offset + txtsz, bsssz);
			setsym(fp, ph[1].filesz, 0, ph[1].memsz, ph[1].offset);
			free(ph);
			return 1;
		}

		werrstr("No TEXT or DATA sections");
		free(ph);
		return 0;
	}

	settext(fp, ep->elfentry, ph[it].vaddr, ph[it].memsz, ph[it].offset);
	setdata(fp, ph[id].vaddr, ph[id].filesz, ph[id].offset, ph[id].memsz - ph[id].filesz);
	if(is != -1)
		setsym(fp, ph[is].filesz, 0, ph[is].memsz, ph[is].offset);
	free(ph);
	return 1;
}

/*
 * (Free|Net)BSD ARM header.
 */
static int
armdotout(int fd, Fhdr *fp, ExecHdr *hp)
{
	uvlong kbase;

	USED(fd);
	settext(fp, hp->e.entry, sizeof(Exec), hp->e.text, sizeof(Exec));
	setdata(fp, fp->txtsz, hp->e.data, fp->txtsz, hp->e.bss);
	setsym(fp, hp->e.syms, hp->e.spsz, hp->e.pcsz, fp->datoff+fp->datsz);

	kbase = 0xF0000000;
	if ((fp->entry & kbase) == kbase) {		/* Boot image */
		fp->txtaddr = kbase+sizeof(Exec);
		fp->name = "ARM *BSD boot image";
		fp->hdrsz = 0;		/* header stripped */
		fp->dataddr = kbase+fp->txtsz;
	}
	return 1;
}

static void
settext(Fhdr *fp, uvlong e, uvlong a, long s, vlong off)
{
	fp->txtaddr = a;
	fp->entry = e;
	fp->txtsz = s;
	fp->txtoff = off;
}

static void
setdata(Fhdr *fp, uvlong a, long s, vlong off, long bss)
{
	fp->dataddr = a;
	fp->datsz = s;
	fp->datoff = off;
	fp->bsssz = bss;
}

static void
setsym(Fhdr *fp, long symsz, long sppcsz, long lnpcsz, vlong symoff)
{
	fp->symsz = symsz;
	fp->symoff = symoff;
	fp->sppcsz = sppcsz;
	fp->sppcoff = fp->symoff+fp->symsz;
	fp->lnpcsz = lnpcsz;
	fp->lnpcoff = fp->sppcoff+fp->sppcsz;
}


static uvlong
_round(uvlong a, ulong b)
{
	uvlong w;

	w = (a/b)*b;
	if (a!=w)
		w += b;
	return(w);
}