Fix run_elf (still leaking memory now).

Makefile

@@ -92,7 +92,7 @@ fs.img: kernel.bin tools/mkfs user/false user/greet user/div0 user/shout
 LDFLAGS=-m elf_i386
 
 user/%: user/%.o user/crt.o
-	$(LD) $(LDFLAGS) -o $@ -Ttext 0x10000 $^
+	$(LD) $(LDFLAGS) -o $@ -Ttext 0x401000 $^
 
 image.bin: mbr.bin fs.img
 	cat $^ >$@

cpu/gdt.c

@@ -1,4 +1,6 @@
 #include "gdt.h"
+#include "x86.h"
+#include "memlayout.h"
 #include "../lib/string.h"
 #include "kernel/mem.h"
 
@@ -52,7 +54,7 @@ void load_gdt() {
     asm("lgdt %0": : "m"(gdt_desc));
 }
 
-void switchuvm(struct taskstate *tss, void* esp) {
+void switchuvm(struct taskstate *tss, void* esp, pde_t *pgdir) {
     memset(tss, 0, sizeof(*tss));
     seg_desc[SEG_TSS] = SEG16(STS_T32A, tss, sizeof(*tss)-1, 0);
     seg_desc[SEG_TSS].s = 0;
@@ -63,4 +65,6 @@ void switchuvm(struct taskstate *tss, void* esp) {
     tss->iomb = (ushort) 0xFFFF;
 
     asm("ltr %0": : "r"((ushort)(SEG_TSS << 3)));
+
+    lcr3(V2P(pgdir));
 }

cpu/gdt.h

@@ -29,6 +29,7 @@
 #define KERN_STACK_BASE  0x90000
 
 #ifndef __ASSEMBLER__
+#include "kernel/mem.h"
 typedef unsigned uint;
 typedef unsigned short ushort;
 
@@ -73,5 +74,5 @@ struct taskstate {
 };
 
 void load_gdt();
-void switchuvm(struct taskstate *tss, void* esp);
+void switchuvm(struct taskstate *tss, void* esp, pde_t *pgdir);
 #endif

cpu/memlayout.h

@@ -5,7 +5,9 @@
 #define PHYSTOP  0x8000000
 
 #define PGROUNDUP(sz)  (((sz)+PGSIZE-1) & ~(PGSIZE-1))
+#define PGROUNDDOWN(a) (((a)) & ~((uintptr_t)(PGSIZE-1)))
 
+#define PTXSHIFT        12      // offset of PTX in a linear address
 #define PDXSHIFT        22      // offset of PDX in a linear address
 
 #define PXMASK          0x3FF
@@ -17,6 +19,12 @@
 
 // page directory index
 #define PDX(va)         (((uintptr_t)(va) >> PDXSHIFT) & PXMASK)
+
+// page table index
+#define PTX(va)         (((uintptr_t)(va) >> PTXSHIFT) & PXMASK)
+
+// Address in page table or page directory entry
+#define PTE_ADDR(pte)   ((uintptr_t)(pte) & ~0xFFF)
 #endif
 
 // Page table/directory entry flags.

kernel/mem.h

@@ -11,4 +11,7 @@ void freerange(void *vstart, void *vend);
 void* kalloc(void);
 void kfree(char*);
 
+pde_t *setupkvm();
 void kvmalloc();
+void switchkvm();
+int allocuvm(pde_t *pgdir, uintptr_t base, uintptr_t top);

kernel/vm.c

@@ -1,11 +1,12 @@
 #include "mem.h"
 #include "cpu/memlayout.h"
 #include "cpu/x86.h"
+#include "console.h"
 
 pde_t *kvm;
 
-void kvmalloc() {
-    kvm = kalloc();
+pde_t *setupkvm(void) {
+    pde_t *kvm = kalloc();
     memset(kvm, 0, PGSIZE);
 
     // Map physical memory to KERNBASE..KERNBASE+PHYSTOP
@@ -13,6 +14,81 @@ void kvmalloc() {
         uintptr_t va = KERNBASE + pa;
         kvm[PDX(va)] = pa | PTE_P | PTE_W | PTE_PS;
     }
-
-    lcr3(V2P(kvm));
+    return kvm;
+}
+
+void kvmalloc() {
+    kvm = setupkvm();
+    switchkvm();
+}
+
+void switchkvm(void)
+{
+    lcr3(V2P(kvm)); // switch to the kernel page table
+}
+
+// Return the address of the PTE in page table pgdir
+// that corresponds to virtual address va.  If alloc!=0,
+// create any required page table pages.
+static pte_t *
+walkpgdir(pde_t *pgdir, const void *va, int alloc)
+{
+    pde_t *pde;
+    pte_t *pgtab;
+
+    pde = &pgdir[PDX(va)];
+    if (*pde & PTE_P) {
+        pgtab = (pte_t *)P2V(PTE_ADDR(*pde));
+    } else {
+        if (!alloc || (pgtab = (pte_t *)kalloc()) == 0)
+            return 0;
+        // Make sure all those PTE_P bits are zero.
+        memset(pgtab, 0, PGSIZE);
+        // The permissions here are overly generous, but they can
+        // be further restricted by the permissions in the page table
+        // entries, if necessary.
+        *pde = V2P(pgtab) | PTE_P | PTE_W | PTE_U;
+    }
+  return &pgtab[PTX(va)];
+}
+
+// Create PTEs for virtual addresses starting at va that refer to
+// physical addresses starting at pa. va and size might not
+// be page-aligned.
+static int
+mappages(pde_t *pgdir, void *va, uintptr_t size, uintptr_t pa, int perm)
+{
+    char *a, *last;
+    pte_t *pte;
+
+    a = (char *)PGROUNDDOWN((uintptr_t)va);
+    last = (char *)PGROUNDDOWN(((uintptr_t)va) + size - 1);
+    for (;;)
+    {
+        if ((pte = walkpgdir(pgdir, a, 1)) == 0)
+            return -1;
+        if (*pte & PTE_P)
+            panic("remap");
+        *pte = pa | perm | PTE_P;
+        if (a == last)
+            break;
+        a += PGSIZE;
+        pa += PGSIZE;
+  }
+  return 0;
+}
+
+int allocuvm(pde_t *pgdir, uintptr_t base, uintptr_t top) {
+    for (uintptr_t a = PGROUNDUP(base); a < top; a += PGSIZE) {
+        char *pa = kalloc();
+        if (pa == 0) {
+            return -1;
+        }
+        memset(pa, 0, PGSIZE);
+        if (mappages(pgdir, (void*)a, PGSIZE, V2P(pa), PTE_W | PTE_U) < 0) {
+            kfree(pa);
+            return -1;
+        }
+    }
+    return 0;
 }

proc.c

@@ -3,6 +3,7 @@
 #include "fs/fs.h"
 #include "cpu/gdt.h"
 #include "cpu/isr.h"
+#include "cpu/memlayout.h"
 #include "kernel/mem.h"
 #include "lib/string.h"
 #include "console.h"
@@ -43,7 +44,10 @@ void run_elf(const char* name) {
     }
     if (!vm.user_task) {
         vm.user_task = kalloc();
-        switchuvm(&vm.user_task->tss, vm.user_task->stack.bottom);
+        vm.user_task->pgdir = setupkvm();
+        allocuvm(vm.user_task->pgdir, USER_BASE, USER_BASE + statbuf.size);
+        allocuvm(vm.user_task->pgdir, USER_STACK_BASE - 2 * PGSIZE, USER_STACK_BASE);
+        switchuvm(&vm.user_task->tss, vm.user_task->stack.bottom, vm.user_task->pgdir);
     }
     if (read_file(&statbuf, (void*)USER_BASE, 100 << 20) <= 0) {
         printk(name);
@@ -75,6 +79,7 @@ void run_elf(const char* name) {
 
 _Noreturn void killproc() {
     void* task_stack;
+    switchkvm();
     swtch(&task_stack, vm.kernel_thread);
     __builtin_unreachable();
 }