--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/source/exec.c	Sun Jan 06 19:27:03 2019 +0900
@@ -0,0 +1,104 @@
+#include "types.h"
+#include "param.h"
+#include "memlayout.h"
+#include "mmu.h"
+#include "proc.h"
+#include "defs.h"
+#include "arm.h"
+#include "elf.h"
+
+int
+exec(char *path, char **argv)
+{
+  char *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()) == 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;
+
+//cprintf("Exec is called argc=%d sz=%x\n", argc, sz);
+
+  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;*/
+  last = argv[0];
+  safestrcpy(curr_proc->name, last, sizeof(curr_proc->name));
+
+  // Commit to the user image.
+  oldpgdir = curr_proc->pgdir;
+  curr_proc->pgdir = pgdir;
+  curr_proc->sz = sz;
+  curr_proc->tf->pc = elf.entry;  // main
+  curr_proc->tf->sp = sp;
+  curr_proc->tf->r0 = ustack[1];
+  curr_proc->tf->r1 = ustack[2];
+  switchuvm(curr_proc);
+  freevm(oldpgdir);
+  return 0;
+
+ bad:
+  if(pgdir)
+    freevm(pgdir);
+  if(ip)
+    iunlockput(ip);
+  return -1;
+}