1 files changed, 33 insertions, 44 deletions

diff --git a/exec.c b/exec.c
index 4f11695..05f80f8 100644
--- a/exec.c
+++ b/exec.c
@@ -9,20 +9,18 @@
 int
 exec(char *path, char **argv)
 {
-  char *mem, *s, *last;
-  int i, argc, arglen, len, off;
-  uint sz, sp, spoffset, argp;
+  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;
 
-  pgdir = 0;
-  sz = 0;
-
   if((ip = namei(path)) == 0)
     return -1;
   ilock(ip);
+  pgdir = 0;
 
   // Check ELF header
   if(readi(ip, (char*)&elf, 0, sizeof(elf)) < sizeof(elf))
@@ -30,10 +28,11 @@ exec(char *path, char **argv)
   if(elf.magic != ELF_MAGIC)
     goto bad;
 
-  if (!(pgdir = setupkvm()))
+  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;
@@ -41,49 +40,39 @@ exec(char *path, char **argv)
       continue;
     if(ph.memsz < ph.filesz)
       goto bad;
-    if (!allocuvm(pgdir, (char *)ph.va, ph.memsz))
+    if((sz = allocuvm(pgdir, sz, ph.va + ph.memsz)) == 0)
       goto bad;
-    if(ph.va + ph.memsz > sz)
-      sz = ph.va + ph.memsz;
-    if (!loaduvm(pgdir, (char *)ph.va, ip, ph.offset, ph.filesz))
+    if(loaduvm(pgdir, (char*)ph.va, ip, ph.offset, ph.filesz) < 0)
       goto bad;
   }
   iunlockput(ip);
+  ip = 0;
 
-  // Allocate and initialize stack at sz
+  // Allocate a one-page stack at the next page boundary
   sz = PGROUNDUP(sz);
-  sz += PGSIZE; // leave an invalid page
-  if (!allocuvm(pgdir, (char *)sz, PGSIZE))
+  if((sz = allocuvm(pgdir, sz, sz + PGSIZE)) == 0)
     goto bad;
-  mem = uva2ka(pgdir, (char *)sz);
-  spoffset = sz;
-  sz += PGSIZE;
-
-  arglen = 0;
-  for(argc=0; argv[argc]; argc++)
-    arglen += strlen(argv[argc]) + 1;
-  arglen = (arglen+3) & ~3;
 
+  // Push argument strings, prepare rest of stack in ustack.
   sp = sz;
-  argp = sz - arglen - 4*(argc+1);
-
-  // Copy argv strings and pointers to stack.
-  *(uint*)(mem+argp-spoffset + 4*argc) = 0;  // argv[argc]
-  for(i=argc-1; i>=0; i--){
-    len = strlen(argv[i]) + 1;
-    sp -= len;
-    memmove(mem+sp-spoffset, argv[i], len);
-    *(uint*)(mem+argp-spoffset + 4*i) = sp;  // argv[i]
+  for(argc = 0; argv[argc]; argc++) {
+    if(argc >= MAXARG)
+      goto bad;
+    sp -= strlen(argv[argc]) + 1;
+    sp &= ~3;
+    if(copyout(pgdir, sp, argv[argc], strlen(argv[argc]) + 1) < 0)
+      goto bad;
+    ustack[3+argc] = sp;
   }
+  ustack[3+argc] = 0;
 
-  // Stack frame for main(argc, argv), below arguments.
-  sp = argp;
-  sp -= 4;
-  *(uint*)(mem+sp-spoffset) = argp;
-  sp -= 4;
-  *(uint*)(mem+sp-spoffset) = argc;
-  sp -= 4;
-  *(uint*)(mem+sp-spoffset) = 0xffffffff;   // fake return pc
+  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++)
@@ -97,15 +86,15 @@ exec(char *path, char **argv)
   proc->sz = sz;
   proc->tf->eip = elf.entry;  // main
   proc->tf->esp = sp;
-
-  switchuvm(proc); 
-
+  switchuvm(proc);
   freevm(oldpgdir);
 
   return 0;
 
  bad:
-  if (pgdir) freevm(pgdir);
-  iunlockput(ip);
+  if(pgdir)
+    freevm(pgdir);
+  if(ip)
+    iunlockput(ip);
   return -1;
 }