exec.c

#include "types.h"
#include "param.h"
#include "memlayout.h"
#include "mmu.h"
#include "proc.h"
#include "defs.h"
#include "x86.h"
#include "elf.h"

int
exec(char *path, char **argv)
{
	char *         s, *last;
	int            i, off;
	uint           argc, sz, sp, ustack[3 + MAXARG + 1];
	struct elfhdr  elf;
	struct inode * ip;
	struct proghdr ph;
	pde_t *        pgdir, *oldpgdir;
	struct proc *  curproc = myproc();

	begin_op();

	if ((ip = namei(path)) == 0) {
		end_op();
		cprintf("exec: fail\n");
		return -1;
	}
	ilock(ip);
	pgdir = 0;

	// Check ELF header
	if (readi(ip, (char *)&elf, 0, sizeof(elf)) != sizeof(elf)) goto bad;
	if (elf.magic != ELF_MAGIC) goto bad;

	if ((pgdir = setupkvm()) == 0) goto bad;

	// Load program into memory.
	sz = 0;
	for (i = 0, off = elf.phoff; i < elf.phnum; i++, off += sizeof(ph)) {
		if (readi(ip, (char *)&ph, off, sizeof(ph)) != sizeof(ph)) goto bad;
		if (ph.type != ELF_PROG_LOAD) continue;
		if (ph.memsz < ph.filesz) goto bad;
		if (ph.vaddr + ph.memsz < ph.vaddr) goto bad;
		if ((sz = allocuvm(pgdir, sz, ph.vaddr + ph.memsz)) == 0) goto bad;
		if (ph.vaddr % PGSIZE != 0) goto bad;
		if (loaduvm(pgdir, (char *)ph.vaddr, ip, ph.off, ph.filesz) < 0) goto bad;
	}
	iunlockput(ip);
	end_op();
	ip = 0;

	// Allocate two pages at the next page boundary.
	// Make the first inaccessible.  Use the second as the user stack.
	sz = PGROUNDUP(sz);
	if ((sz = allocuvm(pgdir, sz, sz + 2 * PGSIZE)) == 0) goto bad;
	clearpteu(pgdir, (char *)(sz - 2 * PGSIZE));
	sp = sz;

	// Push argument strings, prepare rest of stack in ustack.
	for (argc = 0; argv[argc]; argc++) {
		if (argc >= MAXARG) goto bad;
		sp = (sp - (strlen(argv[argc]) + 1)) & ~3;
		if (copyout(pgdir, sp, argv[argc], strlen(argv[argc]) + 1) < 0) goto bad;
		ustack[3 + argc] = sp;
	}
	ustack[3 + argc] = 0;

	ustack[0] = 0xffffffff; // fake return PC
	ustack[1] = argc;
	ustack[2] = sp - (argc + 1) * 4; // argv pointer

	sp -= (3 + argc + 1) * 4;
	if (copyout(pgdir, sp, ustack, (3 + argc + 1) * 4) < 0) goto bad;

	// Save program name for debugging.
	for (last = s = path; *s; s++)
		if (*s == '/') last = s + 1;
	safestrcpy(curproc->name, last, sizeof(curproc->name));

	// Commit to the user image.
	oldpgdir         = curproc->pgdir;
	curproc->pgdir   = pgdir;
	curproc->sz      = sz;
	curproc->tf->eip = elf.entry; // main
	curproc->tf->esp = sp;
	switchuvm(curproc);
	freevm(oldpgdir);
	return 0;

bad:
	if (pgdir) freevm(pgdir);
	if (ip) {
		iunlockput(ip);
		end_op();
	}
	return -1;
}