Use static page table for boot, mapping first 4Mbyte; no more segment…

… trick

Allocate proper kernel page table immediately in main using boot allocator
Remove pginit
Simplify address space layout a tiny bit
More to come (e.g., superpages to simplify static table)

Makefile

@@ -72,7 +72,8 @@ AS = $(TOOLPREFIX)gas
 LD = $(TOOLPREFIX)ld
 OBJCOPY = $(TOOLPREFIX)objcopy
 OBJDUMP = $(TOOLPREFIX)objdump
-CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -O2 -Wall -MD -ggdb -m32 -Werror -fno-omit-frame-pointer
+#CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -O2 -Wall -MD -ggdb -m32 -Werror -fno-omit-frame-pointer
+CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -Wall -MD -ggdb -m32 -Werror -fno-omit-frame-pointer
 CFLAGS += $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
 ASFLAGS = -m32 -gdwarf-2 -Wa,-divide
 # FreeBSD ld wants ``elf_i386_fbsd''
@@ -198,7 +199,7 @@ QEMUGDB = $(shell if $(QEMU) -help | grep -q '^-gdb'; \
 	then echo "-gdb tcp::$(GDBPORT)"; \
 	else echo "-s -p $(GDBPORT)"; fi)
 ifndef CPUS
-CPUS := 2
+CPUS := 1
 endif
 QEMUOPTS = -hdb fs.img xv6.img -smp $(CPUS) -m 512
 

defs.h

@@ -62,7 +62,7 @@ extern uchar    ioapicid;
 void            ioapicinit(void);
 
 // kalloc.c
-char*           pgalloc(void);
+char*           boot_alloc(void);
 char*           kalloc(void);
 void            kfree(char*);
 void            kinit(void);
@@ -161,11 +161,10 @@ void            uartintr(void);
 void            uartputc(int);
 
 // vm.c
-void            pginit(char* (*alloc)());
 void            seginit(void);
 void            kvmalloc(void);
 void            vmenable(void);
-pde_t*          setupkvm(void);
+pde_t*          setupkvm(char* (*alloc)());
 char*           uva2ka(pde_t*, char*);
 int             allocuvm(pde_t*, uint, uint);
 int             deallocuvm(pde_t*, uint, uint);

exec.c

@@ -29,7 +29,7 @@ exec(char *path, char **argv)
   if(elf.magic != ELF_MAGIC)
     goto bad;
 
-  if((pgdir = setupkvm()) == 0)
+  if((pgdir = setupkvm(kalloc)) == 0)
     goto bad;
 
   // Load program into memory.

kalloc.c

@@ -23,11 +23,13 @@ char *newend;
 
 // simple page allocator to get off the ground during boot
 char *
-pgalloc(void)
+boot_alloc(void)
 {
   if (newend == 0)
     newend = end;
 
+  if ((uint) newend >= KERNBASE + 0x400000)
+    panic("only first 4Mbyte are mapped during boot");
   void *p = (void*)PGROUNDUP((uint)newend);
   memset(p, 0, PGSIZE);
   newend = newend + PGSIZE;