From 7fd1f1eb0aab4d52852fc4f5e83eafc991f9a627 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Fri, 31 May 2019 12:43:20 -0400
Subject: exec compiles but argstr() doesn't work yet

---
 proc.c | 50 ++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 38 insertions(+), 12 deletions(-)

(limited to 'proc.c')

diff --git a/proc.c b/proc.c
index a099e98..f0120c2 100644
--- a/proc.c
+++ b/proc.c
@@ -94,26 +94,54 @@ found:
   }
 
   // An empty user page table.
-  p->pagetable = uvmcreate();
+  p->pagetable = proc_pagetable(p);
+
+  // Set up new context to start executing at forkret,
+  // which returns to user space.
+  memset(&p->context, 0, sizeof p->context);
+  p->context.ra = (uint64)forkret;
+  p->context.sp = (uint64)p->kstack + PGSIZE;
+
+  return p;
+}
+
+// Create a page table for a given process,
+// with no users pages, but with trampoline pages.
+// Called both when creating a process, and
+// by exec() when building tentative new memory image,
+// which might fail.
+pagetable_t
+proc_pagetable(struct proc *p)
+{
+  pagetable_t pagetable;
+
+  // An empty user page table.
+  pagetable = uvmcreate();
 
   // map the trampoline code (for system call return)
   // at the highest user virtual address.
   // only the supervisor uses it, on the way
   // to/from user space, so not PTE_U.
-  mappages(p->pagetable, TRAMPOLINE, PGSIZE,
+  mappages(pagetable, TRAMPOLINE, PGSIZE,
            (uint64)trampstart, PTE_R | PTE_X);
 
   // map the trapframe, for trampoline.S.
-  mappages(p->pagetable, (TRAMPOLINE - PGSIZE), PGSIZE,
+  mappages(pagetable, (TRAMPOLINE - PGSIZE), PGSIZE,
            (uint64)(p->tf), PTE_R | PTE_W);
 
-  // Set up new context to start executing at forkret,
-  // which returns to user space.
-  memset(&p->context, 0, sizeof p->context);
-  p->context.ra = (uint64)forkret;
-  p->context.sp = (uint64)p->kstack + PGSIZE;
+  return pagetable;
+}
 
-  return p;
+// Free a process's page table, and free the
+// physical memory the page table refers to.
+// Called both when a process exits and from
+// exec() if it fails.
+void
+proc_freepagetable(pagetable_t pagetable, uint64 sz)
+{
+  unmappages(pagetable, TRAMPOLINE, PGSIZE, 0);
+  unmappages(pagetable, TRAMPOLINE-PGSIZE, PGSIZE, 0);
+  uvmfree(pagetable, sz);
 }
 
 // a user program that calls exec("/init")
@@ -295,9 +323,7 @@ wait(void)
         np->kstack = 0;
         kfree((void*)np->tf);
         np->tf = 0;
-        unmappages(np->pagetable, TRAMPOLINE, PGSIZE, 0);
-        unmappages(np->pagetable, TRAMPOLINE-PGSIZE, PGSIZE, 0);
-        uvmfree(np->pagetable, np->sz);
+        proc_freepagetable(np->pagetable, np->sz);
         np->pagetable = 0;
         np->pid = 0;
         np->parent = 0;
-- 
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