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

#include	<u.h>
#include	<libc.h>
#include	<bio.h>
#include	<bootexec.h>
#include	<mach.h>
#include	"elf.h"

/*
 *	All a.out header types.  The dummy entry allows canonical
 *	processing of the union as a sequence of longs
 */

typedef struct {
	union{
		struct {
			Exec;		/* a.out.h */
			uvlong hdr[1];
		};
		Ehdr;			/* elf.h */
		struct mipsexec;	/* bootexec.h */
		struct mips4kexec;	/* bootexec.h */
		struct sparcexec;	/* bootexec.h */
		struct nextexec;	/* bootexec.h */
	} e;
	long dummy;			/* padding to ensure extra long */
} ExecHdr;

static	int	nextboot(int, Fhdr*, ExecHdr*);
static	int	sparcboot(int, Fhdr*, ExecHdr*);
static	int	mipsboot(int, Fhdr*, ExecHdr*);
static	int	mips4kboot(int, Fhdr*, ExecHdr*);
static	int	common(int, Fhdr*, ExecHdr*);
static	int	commonllp64(int, Fhdr*, ExecHdr*);
static	int	adotout(int, Fhdr*, ExecHdr*);
static	int	elfdotout(int, Fhdr*, ExecHdr*);
static	int	armdotout(int, Fhdr*, ExecHdr*);
static	void	setsym(Fhdr*, long, long, long, vlong);
static	void	setdata(Fhdr*, uvlong, long, vlong, long);
static	void	settext(Fhdr*, uvlong, uvlong, long, vlong);
static	void	hswal(void*, int, ulong(*)(ulong));
static	uvlong	_round(uvlong, ulong);

/*
 *	definition of per-executable file type structures
 */

typedef struct Exectable{
	long	magic;			/* big-endian magic number of file */
	char	*name;			/* executable identifier */
	char	*dlmname;		/* dynamically loadable module identifier */
	uchar	type;			/* Internal code */
	uchar	_magic;			/* _MAGIC() magic */
	Mach	*mach;			/* Per-machine data */
	long	hsize;			/* header size */
	ulong	(*swal)(ulong);		/* beswal or leswal */
	int	(*hparse)(int, Fhdr*, ExecHdr*);
} ExecTable;

extern	Mach	mmips;
extern	Mach	mmips2le;
extern	Mach	mmips2be;
extern	Mach	msparc;
extern	Mach	msparc64;
extern	Mach	m68020;
extern	Mach	mi386;
extern	Mach	mamd64;
extern	Mach	marm;
extern	Mach	mpower;
extern	Mach	malpha;

ExecTable exectab[] =
{
	{ V_MAGIC,			/* Mips v.out */
		"mips plan 9 executable BE",
		"mips plan 9 dlm BE",
		FMIPS,
		1,
		&mmips,
		sizeof(Exec),
		beswal,
		adotout },
	{ P_MAGIC,			/* Mips 0.out (r3k le) */
		"mips plan 9 executable LE",
		"mips plan 9 dlm LE",
		FMIPSLE,
		1,
		&mmips,
		sizeof(Exec),
		beswal,
		adotout },
	{ M_MAGIC,			/* Mips 4.out */
		"mips 4k plan 9 executable BE",
		"mips 4k plan 9 dlm BE",
		FMIPS2BE,
		1,
		&mmips2be,
		sizeof(Exec),
		beswal,
		adotout },
	{ N_MAGIC,			/* Mips 0.out */
		"mips 4k plan 9 executable LE",
		"mips 4k plan 9 dlm LE",
		FMIPS2LE,
		1,
		&mmips2le,
		sizeof(Exec),
		beswal,
		adotout },
	{ 0x160<<16,			/* Mips boot image */
		"mips plan 9 boot image",
		nil,
		FMIPSB,
		0,
		&mmips,
		sizeof(struct mipsexec),
		beswal,
		mipsboot },
	{ (0x160<<16)|3,		/* Mips boot image */
		"mips 4k plan 9 boot image",
		nil,
		FMIPSB,
		0,
		&mmips2be,
		sizeof(struct mips4kexec),
		beswal,
		mips4kboot },
	{ K_MAGIC,			/* Sparc k.out */
		"sparc plan 9 executable",
		"sparc plan 9 dlm",
		FSPARC,
		1,
		&msparc,
		sizeof(Exec),
		beswal,
		adotout },
	{ 0x01030107, 			/* Sparc boot image */
		"sparc plan 9 boot image",
		nil,
		FSPARCB,
		0,
		&msparc,
		sizeof(struct sparcexec),
		beswal,
		sparcboot },
	{ U_MAGIC,			/* Sparc64 u.out */
		"sparc64 plan 9 executable",
		"sparc64 plan 9 dlm",
		FSPARC64,
		1,
		&msparc64,
		sizeof(Exec),
		beswal,
		adotout },
	{ A_MAGIC,			/* 68020 2.out & boot image */
		"68020 plan 9 executable",
		"68020 plan 9 dlm",
		F68020,
		1,
		&m68020,
		sizeof(Exec),
		beswal,
		common },
	{ 0xFEEDFACE,			/* Next boot image */
		"next plan 9 boot image",
		nil,
		FNEXTB,
		0,
		&m68020,
		sizeof(struct nextexec),
		beswal,
		nextboot },
	{ I_MAGIC,			/* I386 8.out & boot image */
		"386 plan 9 executable",
		"386 plan 9 dlm",
		FI386,
		1,
		&mi386,
		sizeof(Exec),
		beswal,
		common },
	{ S_MAGIC,			/* amd64 6.out & boot image */
		"amd64 plan 9 executable",
		"amd64 plan 9 dlm",
		FAMD64,
		1,
		&mamd64,
		sizeof(Exec)+8,
		nil,
		commonllp64 },
	{ Q_MAGIC,			/* PowerPC q.out & boot image */
		"power plan 9 executable",
		"power plan 9 dlm",
		FPOWER,
		1,
		&mpower,
		sizeof(Exec),
		beswal,
		common },
	{ ELF_MAG,			/* any elf32 */
		"elf executable",
		nil,
		FNONE,
		0,
		&mi386,
		sizeof(Ehdr),
		nil,
		elfdotout },
	{ E_MAGIC,			/* Arm 5.out */
		"arm plan 9 executable",
		"arm plan 9 dlm",
		FARM,
		1,
		&marm,
		sizeof(Exec),
		beswal,
		common },
	{ (143<<16)|0413,		/* (Free|Net)BSD Arm */
		"arm *bsd executable",
		nil,
		FARM,
		0,
		&marm,
		sizeof(Exec),
		leswal,
		armdotout },
	{ L_MAGIC,			/* alpha 7.out */
		"alpha plan 9 executable",
		"alpha plan 9 dlm",
		FALPHA,
		1,
		&malpha,
		sizeof(Exec),
		beswal,
		common },
	{ 0x0700e0c3,			/* alpha boot image */
		"alpha plan 9 boot image",
		nil,
		FALPHA,
		0,
		&malpha,
		sizeof(Exec),
		beswal,
		common },
	{ 0 },
};

Mach	*mach = &mi386;			/* Global current machine table */

static ExecTable*
couldbe4k(ExecTable *mp)
{
	Dir *d;
	ExecTable *f;

	if((d=dirstat("/proc/1/regs")) == nil)
		return mp;
	if(d->length < 32*8){		/* R3000 */
		free(d);
		return mp;
	}
	free(d);
	for (f = exectab; f->magic; f++)
		if(f->magic == M_MAGIC) {
			f->name = "mips plan 9 executable on mips2 kernel";
			return f;
		}
	return mp;
}

int
crackhdr(int fd, Fhdr *fp)
{
	ExecTable *mp;
	ExecHdr d;
	int nb, ret;
	ulong magic;

	fp->type = FNONE;
	nb = read(fd, (char *)&d.e, sizeof(d.e));
	if (nb <= 0)
		return 0;

	ret = 0;
	magic = beswal(d.e.magic);		/* big-endian */
	for (mp = exectab; mp->magic; mp++) {
		if (nb < mp->hsize)
			continue;

		/*
		 * The magic number has morphed into something
		 * with fields (the straw was DYN_MAGIC) so now
		 * a flag is needed in Fhdr to distinguish _MAGIC()
		 * magic numbers from foreign magic numbers.
		 *
		 * This code is creaking a bit and if it has to
		 * be modified/extended much more it's probably
		 * time to step back and redo it all.
		 */
		if(mp->_magic){
			if(mp->magic != (magic & ~DYN_MAGIC))
				continue;

			if(mp->magic == V_MAGIC)
				mp = couldbe4k(mp);

			if ((magic & DYN_MAGIC) && mp->dlmname != nil)
				fp->name = mp->dlmname;
			else
				fp->name = mp->name;
		}
		else{
			if(mp->magic != magic)
				continue;
			fp->name = mp->name;
		}
		fp->type = mp->type;
		fp->hdrsz = mp->hsize;		/* will be zero on bootables */
		fp->_magic = mp->_magic;
		fp->magic = magic;

		mach = mp->mach;
		if(mp->swal != nil)
			hswal(&d, sizeof(d.e)/sizeof(ulong), mp->swal);
		ret = mp->hparse(fd, fp, &d);
		seek(fd, mp->hsize, 0);		/* seek to end of header */
		break;
	}
	if(mp->magic == 0)
		werrstr("unknown header type");
	return ret;
}

/*
 * Convert header to canonical form
 */
static void
hswal(void *v, int n, ulong (*swap)(ulong))
{
	ulong *ulp;

	for(ulp = v; n--; ulp++)
		*ulp = (*swap)(*ulp);
}

/*
 *	Crack a normal a.out-type header
 */
static int
adotout(int fd, Fhdr *fp, ExecHdr *hp)
{
	long pgsize;

	USED(fd);
	pgsize = mach->pgsize;
	settext(fp, hp->e.entry, pgsize+sizeof(Exec),
			hp->e.text, sizeof(Exec));
	setdata(fp, _round(pgsize+fp->txtsz+sizeof(Exec), pgsize),
		hp->e.data, fp->txtsz+sizeof(Exec), hp->e.bss);
	setsym(fp, hp->e.syms, hp->e.spsz, hp->e.pcsz, fp->datoff+fp->datsz);
	return 1;
}

static void
commonboot(Fhdr *fp)
{
	if (!(fp->entry & mach->ktmask))
		return;

	switch(fp->type) {				/* boot image */
	case F68020:
		fp->type = F68020B;
		fp->name = "68020 plan 9 boot image";
		break;
	case FI386:
		fp->type = FI386B;
		fp->txtaddr = (u32int)fp->entry;
		fp->name = "386 plan 9 boot image";