i386/junos/MIT/src.xv6/exec.c

   1 #include "types.h"
   2 #include "param.h"
   3 #include "memlayout.h"
   4 #include "mmu.h"
   5 #include "proc.h"
   6 #include "defs.h"
   7 #include "x86.h"
   8 #include "elf.h"
   9
  10 int
  11 exec(char *path, char **argv)
  12 {
  13   char *s, *last;
  14   int i, off;
  15   uint argc, sz, sp, ustack[3+MAXARG+1];
  16   struct elfhdr elf;
  17   struct inode *ip;
  18   struct proghdr ph;
  19   pde_t *pgdir, *oldpgdir;
  20
  21   if((ip = namei(path)) == 0)
  22     return -1;
  23   ilock(ip);
  24   pgdir = 0;
  25
  26   // Check ELF header
  27   if(readi(ip, (char*)&elf, 0, sizeof(elf)) < sizeof(elf))
  28     goto bad;
  29   if(elf.magic != ELF_MAGIC)
  30     goto bad;
  31
  32   if((pgdir = setupkvm(kalloc)) == 0)
  33     goto bad;
  34
  35   // Load program into memory.
  36   sz = 0;
  37   for(i=0, off=elf.phoff; i<elf.phnum; i++, off+=sizeof(ph)){
  38     if(readi(ip, (char*)&ph, off, sizeof(ph)) != sizeof(ph))
  39       goto bad;
  40     if(ph.type != ELF_PROG_LOAD)
  41       continue;
  42     if(ph.memsz < ph.filesz)
  43       goto bad;
  44     if((sz = allocuvm(pgdir, sz, ph.vaddr + ph.memsz)) == 0)
  45       goto bad;
  46     if(loaduvm(pgdir, (char*)ph.vaddr, ip, ph.off, ph.filesz) < 0)
  47       goto bad;
  48   }
  49   iunlockput(ip);
  50   ip = 0;
  51
  52   // Allocate two pages at the next page boundary.
  53   // Make the first inaccessible.  Use the second as the user stack.
  54   sz = PGROUNDUP(sz);
  55   if((sz = allocuvm(pgdir, sz, sz + 2*PGSIZE)) == 0)
  56     goto bad;
  57   clearpteu(pgdir, (char*)(sz - 2*PGSIZE));
  58   sp = sz;
  59
  60   // Push argument strings, prepare rest of stack in ustack.
  61   for(argc = 0; argv[argc]; argc++) {
  62     if(argc >= MAXARG)
  63       goto bad;
  64     sp = (sp - (strlen(argv[argc]) + 1)) & ~3;
  65     if(copyout(pgdir, sp, argv[argc], strlen(argv[argc]) + 1) < 0)
  66       goto bad;
  67     ustack[3+argc] = sp;
  68   }
  69   ustack[3+argc] = 0;
  70
  71   ustack[0] = 0xffffffff;  // fake return PC
  72   ustack[1] = argc;
  73   ustack[2] = sp - (argc+1)*4;  // argv pointer
  74
  75   sp -= (3+argc+1) * 4;
  76   if(copyout(pgdir, sp, ustack, (3+argc+1)*4) < 0)
  77     goto bad;
  78
  79   // Save program name for debugging.
  80   for(last=s=path; *s; s++)
  81     if(*s == '/')
  82       last = s+1;
  83   safestrcpy(proc->name, last, sizeof(proc->name));
  84
  85   // Commit to the user image.
  86   oldpgdir = proc->pgdir;
  87   proc->pgdir = pgdir;
  88   proc->sz = sz;
  89   proc->tf->eip = elf.entry;  // main
  90   proc->tf->esp = sp;
  91   switchuvm(proc);
  92   freevm(oldpgdir);
  93   return 0;
  94
  95  bad:
  96   if(pgdir)
  97     freevm(pgdir);
  98   if(ip)
  99     iunlockput(ip);
 100   return -1;
 101 }