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;

    if ((ip = namei (path)) == 0)
        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 (kalloc)) == 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 ((sz = allocuvm (pgdir, sz, ph.vaddr + ph.memsz)) == 0)
            goto bad;
        if (loaduvm (pgdir, (char *) ph.vaddr, ip, ph.off, ph.filesz) < 0)
            goto bad;
    }
    iunlockput (ip);
    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 (proc->name, last, sizeof (proc->name));

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

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