diff --git a/.gdbinit.tmpl-riscv b/.gdbinit.tmpl-riscv
new file mode 100644
index 0000000..6ea36e1
--- /dev/null
+++ b/.gdbinit.tmpl-riscv
@@ -0,0 +1,3 @@
+set architecture riscv
+target remote 127.0.0.1:1234
+symbol-file kernel
diff --git a/Makefile b/Makefile
index b199842..1424d7c 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,20 @@
 OBJS = \
+  start.o \
+  console.o \
+  uart.o \
+  kalloc.o \
+  spinlock.o \
+  string.o \
+  main.o \
+  vm.o \
+  proc.o \
+  swtch.o \
+  trampoline.o \
+  trap.o \
+  syscall.o \
+  sysproc.o
+
+XXXOBJS = \
 	bio.o\
 	console.o\
 	exec.o\
@@ -28,48 +44,23 @@ OBJS = \
 	vectors.o\
 	vm.o\
 
-# Cross-compiling (e.g., on Mac OS X)
-# TOOLPREFIX = i386-jos-elf
-
-# Using native tools (e.g., on X86 Linux)
+# riscv64-unknown-elf- or riscv64-linux-gnu-
+# perhaps in /opt/riscv/bin
 #TOOLPREFIX = 
 
 # Try to infer the correct TOOLPREFIX if not set
 ifndef TOOLPREFIX
-TOOLPREFIX := $(shell if i386-jos-elf-objdump -i 2>&1 | grep '^elf32-i386$$' >/dev/null 2>&1; \
-	then echo 'i386-jos-elf-'; \
-	elif objdump -i 2>&1 | grep 'elf32-i386' >/dev/null 2>&1; \
-	then echo ''; \
+TOOLPREFIX := $(shell if riscv64-unknown-elf-objdump -i 2>&1 | grep 'elf64-big' >/dev/null 2>&1; \
+	then echo 'riscv64-unknown-elf-'; \
+	elif riscv64-linux-gnu-objdump -i 2>&1 | grep 'elf64-big' >/dev/null 2>&1; \
+	then echo 'riscv64-linux-gnu-'; \
 	else echo "***" 1>&2; \
-	echo "*** Error: Couldn't find an i386-*-elf version of GCC/binutils." 1>&2; \
-	echo "*** Is the directory with i386-jos-elf-gcc in your PATH?" 1>&2; \
-	echo "*** If your i386-*-elf toolchain is installed with a command" 1>&2; \
-	echo "*** prefix other than 'i386-jos-elf-', set your TOOLPREFIX" 1>&2; \
-	echo "*** environment variable to that prefix and run 'make' again." 1>&2; \
+	echo "*** Error: Couldn't find an riscv64 version of GCC/binutils." 1>&2; \
 	echo "*** To turn off this error, run 'gmake TOOLPREFIX= ...'." 1>&2; \
 	echo "***" 1>&2; exit 1; fi)
 endif
 
-# If the makefile can't find QEMU, specify its path here
-QEMU = qemu-system-x86_64
-
-# Try to infer the correct QEMU
-ifndef QEMU
-QEMU = $(shell if which qemu > /dev/null; \
-	then echo qemu; exit; \
-	elif which qemu-system-i386 > /dev/null; \
-	then echo qemu-system-i386; exit; \
-	elif which qemu-system-x86_64 > /dev/null; \
-	then echo qemu-system-x86_64; exit; \
-	else \
-	qemu=/Applications/Q.app/Contents/MacOS/i386-softmmu.app/Contents/MacOS/i386-softmmu; \
-	if test -x $$qemu; then echo $$qemu; exit; fi; fi; \
-	echo "***" 1>&2; \
-	echo "*** Error: Couldn't find a working QEMU executable." 1>&2; \
-	echo "*** Is the directory containing the qemu binary in your PATH" 1>&2; \
-	echo "*** or have you tried setting the QEMU variable in Makefile?" 1>&2; \
-	echo "***" 1>&2; exit 1)
-endif
+QEMU = qemu-system-riscv64
 
 CC = $(TOOLPREFIX)gcc
 AS = $(TOOLPREFIX)gas
@@ -77,15 +68,10 @@ LD = $(TOOLPREFIX)ld
 OBJCOPY = $(TOOLPREFIX)objcopy
 OBJDUMP = $(TOOLPREFIX)objdump
 
-XFLAGS = -m64 -mcmodel=large -ggdb
-# CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -O2 -Wall -MD -ggdb -Werror -fno-omit-frame-pointer
-CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -Wall -MD -ggdb -Werror -fno-omit-frame-pointer
-CFLAGS += -ffreestanding -fno-common -nostdlib $(XFLAGS)
+CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -Wall -MD -ggdb -Werror -fno-omit-frame-pointer -O
+CFLAGS = -mcmodel=medany
+CFLAGS += -ffreestanding -fno-common -nostdlib -mno-relax
 CFLAGS += $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
-ASFLAGS = -gdwarf-2 -Wa,-divide $(XFLAGS)
-# FreeBSD ld wants ``elf_i386_fbsd''
-LDFLAGS += -m $(shell $(LD) -V | grep elf_x86_64 2>/dev/null | head -n 1)
-LDFLAGS += -z max-page-size=4096
 
 # Disable PIE when possible (for Ubuntu 16.10 toolchain)
 ifneq ($(shell $(CC) -dumpspecs 2>/dev/null | grep -e '[^f]no-pie'),)
@@ -95,21 +81,17 @@ ifneq ($(shell $(CC) -dumpspecs 2>/dev/null | grep -e '[^f]nopie'),)
 CFLAGS += -fno-pie -nopie
 endif
 
-kernel: $(OBJS) entry.o entryother initcode kernel.ld
-	$(LD) $(LDFLAGS) -T kernel.ld -o kernel entry.o $(OBJS) -b binary initcode entryother
+LDFLAGS = -z max-page-size=4096
+
+kernel: $(OBJS) entry.o kernel.ld 
+	$(LD) $(LDFLAGS) -T kernel.ld -o kernel entry.o $(OBJS) 
 	$(OBJDUMP) -S kernel > kernel.asm
 	$(OBJDUMP) -t kernel | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > kernel.sym
 
-entryother: entryother.S
-	$(CC) $(CFLAGS) -fno-pic -nostdinc -I. -c entryother.S
-	$(LD) $(LDFLAGS) -N -e start -Ttext 0x7000 -o bootblockother.o entryother.o
-	$(OBJCOPY) -S -O binary -j .text bootblockother.o entryother
-	$(OBJDUMP) -S bootblockother.o > entryother.asm
-
 initcode: initcode.S
 	$(CC) $(CFLAGS) -nostdinc -I. -c initcode.S
-	$(LD) $(LDFLAGS) -N -e start -Ttext 0 -o initcode.out initcode.o
-	$(OBJCOPY) -S -O binary initcode.out initcode
+	#$(LD) $(LDFLAGS) -N -e start -Ttext 0 -o initcode.out initcode.o
+	#$(OBJCOPY) -S -O binary initcode.out initcode
 	$(OBJDUMP) -S initcode.o > initcode.asm
 
 tags: $(OBJS) entryother.S _init
@@ -186,19 +168,18 @@ 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 = -kernel kernel -drive file=fs.img,index=1,media=disk,format=raw -smp $(CPUS) -m 512 $(QEMUEXTRA)
-qemu: fs.img
-	$(QEMU) -serial mon:stdio $(QEMUOPTS)
+QEMUOPTS = -machine virt -kernel kernel -m 3G -smp $(CPUS) -nographic
+#QEMUOPTS += -initrd fs.img
 
-qemu-nox: fs.img kernel
-	$(QEMU) -nographic $(QEMUOPTS)
+qemu: kernel
+	$(QEMU) $(QEMUOPTS)
 
-.gdbinit: .gdbinit.tmpl-x64
-	sed "s/localhost:1234/localhost:$(GDBPORT)/" < $^ > $@
+.gdbinit: .gdbinit.tmpl-riscv
+	sed "s/:1234/:$(GDBPORT)/" < $^ > $@
 
-qemu-gdb: fs.img kernel .gdbinit
+qemu-gdb: kernel .gdbinit
 	@echo "*** Now run 'gdb'." 1>&2
 	$(QEMU) $(QEMUOPTS) -S $(QEMUGDB)
 
diff --git a/console.c b/console.c
index 9986a9c..25a621a 100644
--- a/console.c
+++ b/console.c
@@ -5,17 +5,14 @@
 #include <stdarg.h>
 
 #include "types.h"
-#include "defs.h"
 #include "param.h"
-#include "traps.h"
 #include "spinlock.h"
 #include "sleeplock.h"
 #include "fs.h"
 #include "file.h"
 #include "memlayout.h"
-#include "mmu.h"
-#include "proc.h"
-#include "x86.h"
+#include "riscv.h"
+#include "defs.h"
 
 static void consputc(int);
 
@@ -28,6 +25,12 @@ static struct {
 
 static char digits[] = "0123456789abcdef";
 
+void
+consoleinit(void)
+{
+  initlock(&cons.lock, "console");
+}
+
 static void
 printint(int xx, int base, int sign)
 {
@@ -66,7 +69,7 @@ printptr(uint64 x) {
 
 // Print to the console. only understands %d, %x, %p, %s.
 void
-cprintf(char *fmt, ...)
+printf(char *fmt, ...)
 {
   va_list ap;
   int i, c, locking;
@@ -122,67 +125,20 @@ cprintf(char *fmt, ...)
 void
 panic(char *s)
 {
-  int i;
-  uint64 pcs[10];
-
-  cli();
-  cons.locking = 0;
-  // use lapiccpunum so that we can call panic from mycpu()
-  cprintf("lapicid %d: panic: ", lapicid());
-  cprintf(s);
-  cprintf("\n");
-  getcallerpcs(&s, pcs);
-  for(i=0; i<10; i++)
-    cprintf(" %p", pcs[i]);
+  printf("panic: ");
+  printf(s);
+  printf("\n");
   panicked = 1; // freeze other CPU
   for(;;)
     ;
 }
 
-//PAGEBREAK: 50
 #define BACKSPACE 0x100
-#define CRTPORT 0x3d4
-static ushort *crt = (ushort*)P2V(0xb8000);  // CGA memory
-
-static void
-cgaputc(int c)
-{
-  int pos;
-
-  // Cursor position: col + 80*row.
-  outb(CRTPORT, 14);
-  pos = inb(CRTPORT+1) << 8;
-  outb(CRTPORT, 15);
-  pos |= inb(CRTPORT+1);
-
-  if(c == '\n')
-    pos += 80 - pos%80;
-  else if(c == BACKSPACE){
-    if(pos > 0) --pos;
-  } else
-    crt[pos++] = (c&0xff) | 0x0700;  // black on white
-
-  if(pos < 0 || pos > 25*80)
-    panic("pos under/overflow");
-
-  if((pos/80) >= 24){  // Scroll up.
-    memmove(crt, crt+80, sizeof(crt[0])*23*80);
-    pos -= 80;
-    memset(crt+pos, 0, sizeof(crt[0])*(24*80 - pos));
-  }
-
-  outb(CRTPORT, 14);
-  outb(CRTPORT+1, pos>>8);
-  outb(CRTPORT, 15);
-  outb(CRTPORT+1, pos);
-  crt[pos] = ' ' | 0x0700;
-}
 
 void
 consputc(int c)
 {
   if(panicked){
-    cli();
     for(;;)
       ;
   }
@@ -191,125 +147,4 @@ consputc(int c)
     uartputc('\b'); uartputc(' '); uartputc('\b');
   } else
     uartputc(c);
-  cgaputc(c);
 }
-
-#define INPUT_BUF 128
-struct {
-  char buf[INPUT_BUF];
-  uint r;  // Read index
-  uint w;  // Write index
-  uint e;  // Edit index
-} input;
-
-#define C(x)  ((x)-'@')  // Control-x
-
-void
-consoleintr(int (*getc)(void))
-{
-  int c, doprocdump = 0;
-
-  acquire(&cons.lock);
-  while((c = getc()) >= 0){
-    switch(c){
-    case C('P'):  // Process listing.
-      // procdump() locks cons.lock indirectly; invoke later
-      doprocdump = 1;
-      break;
-    case C('U'):  // Kill line.
-      while(input.e != input.w &&
-            input.buf[(input.e-1) % INPUT_BUF] != '\n'){
-        input.e--;
-        consputc(BACKSPACE);
-      }
-      break;
-    case C('H'): case '\x7f':  // Backspace
-      if(input.e != input.w){
-        input.e--;
-        consputc(BACKSPACE);
-      }
-      break;
-    default:
-      if(c != 0 && input.e-input.r < INPUT_BUF){
-        c = (c == '\r') ? '\n' : c;
-        input.buf[input.e++ % INPUT_BUF] = c;
-        consputc(c);
-        if(c == '\n' || c == C('D') || input.e == input.r+INPUT_BUF){
-          input.w = input.e;
-          wakeup(&input.r);
-        }
-      }
-      break;
-    }
-  }
-  release(&cons.lock);
-  if(doprocdump) {
-    procdump();  // now call procdump() wo. cons.lock held
-  }
-}
-
-int
-consoleread(struct inode *ip, char *dst, int n)
-{
-  uint target;
-  int c;
-
-  iunlock(ip);
-  target = n;
-  acquire(&cons.lock);
-  while(n > 0){
-    while(input.r == input.w){
-      if(myproc()->killed){
-        release(&cons.lock);
-        ilock(ip);
-        return -1;
-      }
-      sleep(&input.r, &cons.lock);
-    }
-    c = input.buf[input.r++ % INPUT_BUF];
-    if(c == C('D')){  // EOF
-      if(n < target){
-        // Save ^D for next time, to make sure
-        // caller gets a 0-byte result.
-        input.r--;
-      }
-      break;
-    }
-    *dst++ = c;
-    --n;
-    if(c == '\n')
-      break;
-  }
-  release(&cons.lock);
-  ilock(ip);
-
-  return target - n;
-}
-
-int
-consolewrite(struct inode *ip, char *buf, int n)
-{
-  int i;
-
-  iunlock(ip);
-  acquire(&cons.lock);
-  for(i = 0; i < n; i++)
-    consputc(buf[i] & 0xff);
-  release(&cons.lock);
-  ilock(ip);
-
-  return n;
-}
-
-void
-consoleinit(void)
-{
-  initlock(&cons.lock, "console");
-
-  devsw[CONSOLE].write = consolewrite;
-  devsw[CONSOLE].read = consoleread;
-  cons.locking = 1;
-
-  ioapicenable(IRQ_KBD, 0);
-}
-
diff --git a/defs.h b/defs.h
index 3735f6f..d86e495 100644
--- a/defs.h
+++ b/defs.h
@@ -19,7 +19,7 @@ void            bwrite(struct buf*);
 
 // console.c
 void            consoleinit(void);
-void            cprintf(char*, ...);
+void            printf(char*, ...);
 void            consoleintr(int(*)(void));
 void            panic(char*) __attribute__((noreturn));
 
@@ -65,10 +65,9 @@ extern uchar    ioapicid;
 void            ioapicinit(void);
 
 // kalloc.c
-char*           kalloc(void);
-void            kfree(char*);
-void            kinit1(void*, void*);
-void            kinit2(void*, void*);
+void*           kalloc(void);
+void            kfree(void *);
+void            kinit();
 
 // kbd.c
 void            kbdintr(void);
@@ -112,7 +111,7 @@ int             kill(int);
 struct cpu*     mycpu(void);
 struct cpu*     getmycpu(void);
 struct proc*    myproc();
-void            pinit(void);
+void            procinit(void);
 void            procdump(void);
 void            scheduler(void) __attribute__((noreturn));
 void            sched(void);
@@ -124,7 +123,7 @@ void            wakeup(void*);
 void            yield(void);
 
 // swtch.S
-void            swtch(struct context**, struct context*);
+void            swtch(struct context*, struct context*);
 
 // spinlock.c
 void            acquire(struct spinlock*);
@@ -158,16 +157,16 @@ int             argaddr(int, uint64 *);
 int             fetchint(uint64, int*);
 int             fetchstr(uint64, char**);
 int             fetchaddr(uint64, uint64*);
-void            syscall(struct sysframe*);
+void            syscall();
 
 // timer.c
 void            timerinit(void);
 
 // trap.c
-void            idtinit(void);
 extern uint     ticks;
-void            tvinit(void);
+void            trapinit(void);
 extern struct spinlock tickslock;
+void            usertrapret(void);
 
 // uart.c
 void            uartinit(void);
@@ -175,20 +174,15 @@ void            uartintr(void);
 void            uartputc(int);
 
 // vm.c
-void            seginit(void);
-void            kvmalloc(void);
-pde_t*          setupkvm(void);
-char*           uva2ka(pde_t*, char*);
-int             allocuvm(pde_t*, uint, uint);
-int             deallocuvm(pde_t*, uint64, uint64);
-void            freevm(pde_t*, uint64);
-void            inituvm(pde_t*, char*, uint);
-int             loaduvm(pde_t*, char*, struct inode*, uint, uint);
-pde_t*          copyuvm(pde_t*, uint);
-void            switchuvm(struct proc*);
-void            switchkvm(void);
-int             copyout(pde_t*, uint, void*, uint);
-void            clearpteu(pde_t *pgdir, char *uva);
+void            kvminit(void);
+void            kvmswitch(void);
+pagetable_t     uvmcreate(void);
+void            uvminit(pagetable_t, char *, uint);
+int             uvmdealloc(pagetable_t, uint64, uint64);
+void            uvmcopy(pagetable_t, pagetable_t, uint64);
+void            uvmfree(pagetable_t, uint64);
+void            mappages(pagetable_t, uint64, uint64, uint64, int);
+void            unmappages(pagetable_t, uint64, uint64, int);
 
 // number of elements in fixed-size array
 #define NELEM(x) (sizeof(x)/sizeof((x)[0]))
diff --git a/entry.S b/entry.S
index 0aacb4c..8b3316c 100644
--- a/entry.S
+++ b/entry.S
@@ -1,223 +1,22 @@
-# x86-64 bootstrap, assuming load by MultiBoot-compliant loader.
-# The MutliBoot specification is at:
-# http://www.gnu.org/software/grub/manual/multiboot/multiboot.html
-# GRUB is a MultiBoot loader, as is qemu's -kernel option.
-
-#include "mmu.h"
-#include "memlayout.h"  
-
-# STACK is the size of the bootstrap stack.
-#define STACK 8192
-
-# MultiBoot header.
-# http://www.gnu.org/software/grub/manual/multiboot/multiboot.html#Header-layout
-.align 4
-.text
-.globl multiboot_header
-multiboot_header:
-  #define magic 0x1badb002
-  #define flags (1<<16 | 1<<0)
-  .long magic
-  .long flags
-  .long (- magic - flags)  # checksum
-  .long V2P_WO(multiboot_header)  # header address
-  .long V2P_WO(multiboot_header)  # load address
-  .long V2P_WO(edata)       # load end address
-  .long V2P_WO(end)         # bss end address
-  .long V2P_WO(start)       # entry address
-
-# Entry point jumped to by boot loader.  Running in 32-bit mode.
-# http://www.gnu.org/software/grub/manual/multiboot/multiboot.html#Machine-state
-#
-#       EAX = 0x2badb002
-#       EBX = address of multiboot information structure
-#       CS = 32-bit read/execute code segment with identity map
-#       DS, ES, FS, GS, SS = 32-bit read/write data segment with identity map
-#       A20 gate = enabled
-#       CR0 = PE set, PG clear
-#       EFLAGS = VM clear, IF clear
-#
-.code32
-.globl start
-start:
-  # Tell BIOS to do "warm reboot" when we shut down.
-  movw $0x1234, 0x472
-
-  # Set up multiboot arguments for main.
-  movl %eax, %edi
-  movl %ebx, %esi
-
-  # Initialize stack.
-  movl $V2P_WO(stack+STACK), %esp
-  
-  # Zero bss.  QEMU's MultiBoot seems not to.
-  # It's possible that the header above is not right, but it looks right.
-  # %edi is holding multiboot argument, so save in another register.
-  # (The stack is in the bss.)
-  movl %edi, %edx
-  movl $V2P_WO(edata), %edi
-  movl $V2P_WO(end), %ecx
-  subl $V2P_WO(edata), %ecx
-  movl $0, %eax
-  cld
-  rep stosb
-  movl %edx, %edi
-
-  call loadgdt
-  
-  # Enter new 32-bit code segment (already in 32-bit mode).
-  ljmp $SEG_KCODE32, $V2P_WO(start32)  // code32 segment selector
-  
-start32:
-  # Initialize page table.
-  call initpagetables
-  call init32e
-  
-  movl $V2P_WO(start64), %eax
-  # Enter 64-bit mode.
-  ljmp $SEG_KCODE, $V2P_WO(tramp64)  // code64 segment selector
-
-.code64
-start64:
-  # Load VA of stack
-  movabsq $(stack+STACK), %rsp
-  # Clear frame pointer for stack walks
-  movl $0, %ebp
-  # Call into C code.
-  call main
-  # should not return from main
-  jmp .
-
-.code32
-.global apstart
-apstart:
-  call loadgdt
-  ljmp $SEG_KCODE32, $V2P_WO(apstart32)  // code32 segment selector
-  
-apstart32:
-  call init32e
-  movl $V2P_WO(apstart64), %eax
-  ljmp $SEG_KCODE, $V2P_WO(tramp64)  // code64 segment selector
-
-.code64       
-apstart64:
-  # Remember (from bootothers), that our kernel stack pointer is
-  # at the top of our temporary stack.
-  popq %rax
-  movq %rax, %rsp
-  movq $0, %rbp
-  call apmain
-  jmp .
-  
-.code64
-tramp64:
-  # The linker thinks we are running at tramp64, but we're actually
-  # running at PADDR(tramp64), so use an explicit calculation to
-  # load and jump to the correct address.  %rax should hold the
-  # physical address of the jmp target.
-  movq $KERNBASE, %r11
-  addq %r11, %rax
-  jmp *%rax
-
-# Initial stack
-.comm stack, STACK
-
-# Page tables.  See section 4.5 of 253668.pdf.
-# We map the first GB of physical memory at 0 and at 1 TB (not GB) before
-# the end of virtual memory.  At boot time we are using the mapping at 0
-# but during ordinary execution we use the high mapping.
-# The intent is that after bootstrap the kernel can expand this mapping
-# to cover all the available physical memory.
-# This would be easier if we could use the PS bit to create GB-sized entries
-# and skip the pdt table, but not all chips support it, and QEMU doesn't.
-.align 4096
-pml4:
-  .quad V2P_WO(pdpt) + PTE_P + PTE_W   // present, read/write
-  .quad 0
-  .space 4096 - 2*16
-  .quad V2P_WO(pdpt) + PTE_P + PTE_W
-  .quad 0
-
-.align 4096
-pdpt:
-  .quad V2P_WO(pdt) + PTE_P + PTE_W
-  .space 4096 - 8
-
-.align 4096
-pdt:
-  // Filled in below.
-  .space 4096
-
-.code32
-initpagetables:
-  pushl %edi
-  pushl %ecx
-  pushl %eax
-
-  // Set up 64-bit entry in %edx:%eax.
-  // Base address 0, present, read/write, large page.
-  movl $(0 | PTE_P | PTE_W | PTE_PS), %eax
-  movl $0, %edx
-
-  // Fill in 512 entries at pdt.
-  movl $V2P_WO(pdt), %edi
-  movl $512, %ecx
-1:
-  // Write this 64-bit entry.
-  movl %eax, 0(%edi)
-  movl %edx, 4(%edi)
-  addl $8, %edi
-  // 64-bit add to prepare address for next entry.
-  // Because this is a large page entry, it covers 512 4k pages (2 MB).
-  add $(512*4096), %eax
-  adc $0, %edx
-  loop 1b
-
-  popl %eax
-  popl %ecx
-  popl %edi
-  ret
-
-# Initialize IA-32e mode.  See section 9.8.5 of 253668.pdf.
-init32e:
-  # Set CR4.PAE and CR4.PSE = 1.
-  movl %cr4, %eax
-  orl $0x30, %eax
-  movl %eax, %cr4
-
-  # Load CR3 with physical base address of level 4 page table.
-  movl $V2P_WO(pml4), %eax
-  movl %eax, %cr3
-  
-  # Enable IA-32e mode by setting IA32_EFER.LME = 1.
-  # Also turn on IA32_EFER.SCE (syscall enable).
-  movl $0xc0000080, %ecx
-  rdmsr
-  orl $0x101, %eax
-  wrmsr
-
-  # Enable paging by setting CR0.PG = 1.
-  movl %cr0, %eax
-  orl $0x80000000, %eax   
-  movl %eax, %cr0
-  nop
-  nop
-
-  ret
-
-loadgdt:
-  subl $8, %esp
-  movl $V2P_WO(bootgdt), 4(%esp)
-  movw $(8*NSEGS-1), 2(%esp)
-  lgdt 2(%esp)
-  addl $8, %esp
-
-  movl $SEG_KDATA, %eax  // data segment selector
-  movw %ax, %ds
-  movw %ax, %es
-  movw %ax, %ss
-  movl $0, %eax  // null segment selector
-  movw %ax, %fs
-  movw %ax, %gs
-
-  ret
+	# qemu -kernel starts at 0x1000. the instructions
+        # there seem to be provided by qemu, as if it
+        # were a ROM. the code at 0x1000 jumps to
+        # 0x8000000, the _start function here,
+        # in machine mode.
+.section .data
+.globl stack0
+.section .text
+.globl mstart
+.section .text
+.globl _entry
+_entry:
+	# set up a stack for C; stack0 is declared in start.
+        la sp, stack0
+        addi sp, sp, 1024
+        addi sp, sp, 1024
+        addi sp, sp, 1024
+        addi sp, sp, 1024
+	# jump to mstart() in start.c
+        call mstart
+junk:
+        j junk
diff --git a/exec.c b/exec.c
index 743437a..6d0ef24 100644
--- a/exec.c
+++ b/exec.c
@@ -19,8 +19,8 @@ exec(char *path, char **argv)
   struct inode *ip;
   struct proghdr ph;
   pde_t *pgdir, *oldpgdir;
-  struct proc *curproc = myproc();
-  uint64 oldsz = curproc->sz;
+  struct proc *p = myproc();
+  uint64 oldsz = p->sz;
   
   begin_op();
 
@@ -85,8 +85,8 @@ exec(char *path, char **argv)
   ustack[1] = argc;
   ustack[2] = sp - (argc+1)*sizeof(uint64);  // argv pointer
 
-  curproc->sf->rdi = argc;
-  curproc->sf->rsi = sp - (argc+1)*sizeof(uint64);
+  p->sf->rdi = argc;
+  p->sf->rsi = sp - (argc+1)*sizeof(uint64);
 
   sp -= (3+argc+1) * sizeof(uint64);
   if(copyout(pgdir, sp, ustack, (3+argc+1)*sizeof(uint64)) < 0)
@@ -96,15 +96,15 @@ exec(char *path, char **argv)
   for(last=s=path; *s; s++)
     if(*s == '/')
       last = s+1;
-  safestrcpy(curproc->name, last, sizeof(curproc->name));
+  safestrcpy(p->name, last, sizeof(p->name));
     
   // Commit to the user image.
-  oldpgdir = curproc->pgdir;
-  curproc->pgdir = pgdir;
-  curproc->sz = sz;
-  curproc->sf->rcx = elf.entry;  // main
-  curproc->sf->rsp = sp;
-  switchuvm(curproc);
+  oldpgdir = p->pgdir;
+  p->pgdir = pgdir;
+  p->sz = sz;
+  p->sf->rcx = elf.entry;  // main
+  p->sf->rsp = sp;
+  switchuvm(p);
   freevm(oldpgdir, oldsz);
   return 0;
 
diff --git a/initcode.S b/initcode.S
index e097394..ca76972 100644
--- a/initcode.S
+++ b/initcode.S
@@ -2,22 +2,20 @@
 # This code runs in user space.
 
 #include "syscall.h"
-#include "traps.h"
-
 
 # exec(init, argv)
 .globl start
 start:
-  mov $init, %rdi
-  mov $argv, %rsi
-  mov $SYS_exec, %rax  
-  syscall
+        la a0, init
+        la a1, argv
+        li a7, SYS_exec
+        ecall
 
 # for(;;) exit();
 exit:
-  mov $SYS_exit, %rax
-  syscall
-  jmp exit
+        li a7, SYS_exit
+        ecall
+        jal exit
 
 # char init[] = "/init\0";
 init:
@@ -28,4 +26,3 @@ init:
 argv:
   .long init
   .long 0
-
diff --git a/kalloc.c b/kalloc.c
index fb939b7..c943e5e 100644
--- a/kalloc.c
+++ b/kalloc.c
@@ -3,13 +3,14 @@
 // and pipe buffers. Allocates 4096-byte pages.
 
 #include "types.h"
-#include "defs.h"
 #include "param.h"
 #include "memlayout.h"
-#include "mmu.h"
 #include "spinlock.h"
+#include "riscv.h"
+#include "defs.h"
+
+void freerange(void *pa_start, void *pa_end);
 
-void freerange(void *vstart, void *vend);
 extern char end[]; // first address after kernel loaded from ELF file
                    // defined by the kernel linker script in kernel.ld
 
@@ -19,36 +20,22 @@ struct run {
 
 struct {
   struct spinlock lock;
-  int use_lock;
   struct run *freelist;
 } kmem;
 
-// Initialization happens in two phases.
-// 1. main() calls kinit1() while still using entrypgdir to place just
-// the pages mapped by entrypgdir on free list.
-// 2. main() calls kinit2() with the rest of the physical pages
-// after installing a full page table that maps them on all cores.
 void
-kinit1(void *vstart, void *vend)
+kinit()
 {
   initlock(&kmem.lock, "kmem");
-  kmem.use_lock = 0;
-  freerange(vstart, vend);
+  freerange(end, (void*)PHYSTOP);
 }
 
 void
-kinit2(void *vstart, void *vend)
-{
-  freerange(vstart, vend);
-  kmem.use_lock = 1;
-}
-
-void
-freerange(void *vstart, void *vend)
+freerange(void *pa_start, void *pa_end)
 {
   char *p;
-  p = (char*)PGROUNDUP((uint64)vstart);
-  for(; p + PGSIZE <= (char*)vend; p += PGSIZE)
+  p = (char*)PGROUNDUP((uint64)pa_start);
+  for(; p + PGSIZE <= (char*)pa_end; p += PGSIZE)
     kfree(p);
 }
 //PAGEBREAK: 21
@@ -57,42 +44,37 @@ freerange(void *vstart, void *vend)
 // call to kalloc().  (The exception is when
 // initializing the allocator; see kinit above.)
 void
-kfree(char *v)
+kfree(void *pa)
 {
   struct run *r;
 
-  if((uint64)v % PGSIZE || v < end || V2P(v) >= PHYSTOP)
+  if(((uint64)pa % PGSIZE) != 0 || (char*)pa < end || (uint64)pa >= PHYSTOP)
     panic("kfree");
 
   // Fill with junk to catch dangling refs.
-  memset(v, 1, PGSIZE);
+  memset(pa, 1, PGSIZE);
 
-  if(kmem.use_lock)
-    acquire(&kmem.lock);
-  r = (struct run*)v;
+  acquire(&kmem.lock);
+  r = (struct run*)pa;
   r->next = kmem.freelist;
   kmem.freelist = r;
-  if(kmem.use_lock)
-    release(&kmem.lock);
+  release(&kmem.lock);
 }
 
 // Allocate one 4096-byte page of physical memory.
 // Returns a pointer that the kernel can use.
 // Returns 0 if the memory cannot be allocated.
-char*
+void *
 kalloc(void)
 {
   struct run *r;
 
-  if(kmem.use_lock)
-    acquire(&kmem.lock);
+  acquire(&kmem.lock);
   r = kmem.freelist;
   if(r)
     kmem.freelist = r->next;
-  if(kmem.use_lock)
-    release(&kmem.lock);
-  if(r != 0 && (uint64) r < KERNBASE)
-    panic("kalloc");
-  return (char*)r;
+  release(&kmem.lock);
+  memset((char*)r, 5, PGSIZE); // fill with junk
+  return (void*)r;
 }
 
diff --git a/kernel.ld b/kernel.ld
index 11dc98f..08fc280 100644
--- a/kernel.ld
+++ b/kernel.ld
@@ -1,50 +1,33 @@
-OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64", "elf64-x86-64")
-OUTPUT_ARCH(i386:x86-64)
+OUTPUT_ARCH( "riscv" )
+ENTRY( _entry )
 
 SECTIONS
 {
-	. = 0xFFFFFF0000100000;
-	PROVIDE(text = .);
-	.text : AT(0x100000) {
-		*(.text .stub .text.* .gnu.linkonce.t.*)
-	}
-	.rodata : {
-		*(.rodata .rodata.* .gnu.linkonce.r.*)
-	}
+  /*
+   * ensure that entry.S / _entry is at 0x80000000,
+   * where qemu's -kernel jumps.
+   */
+  . = 0x80000000;
+  .text :
+  {
+    *(.text)
+    . = ALIGN(0x1000);
+    *(trampoline)
+  }
 
-	/* Include debugging information in kernel memory */
-	.stab : {
-		PROVIDE(__STAB_BEGIN__ = .);
-		*(.stab);
-		PROVIDE(__STAB_END__ = .);
-		BYTE(0)		/* Force the linker to allocate space
-				   for this section */
-	}
+  . = ALIGN(0x1000);
+  PROVIDE(etext = .);
 
-	.stabstr : {
-		PROVIDE(__STABSTR_BEGIN__ = .);
-		*(.stabstr);
-		PROVIDE(__STABSTR_END__ = .);
-		BYTE(0)		/* Force the linker to allocate space
-				   for this section */
-	}
+  /*
+   * make sure end is after data and bss.
+   */
+  .data : {
+    *(.data)
+  }
+  bss : {
+    *(.bss)
+  }
 
-	. = ALIGN(0x1000);
-
-        /* Conventionally, Unix linkers provide pseudo-symbols
-         * etext, edata, and end, at the end of the text, data, and bss.
-         * For the kernel mapping, we need the address at the beginning
-         * of the data section, but that's not one of the conventional
-         * symbols, because the convention started before there was a
-         * read-only rodata section between text and data. */
-        PROVIDE(data = .);
-	.data : {
-		*(.data)
-	}
-	bss : {
-		PROVIDE(edata = .);
-		*(.bss)
-		*(COMMON)
-		PROVIDE(end = .);
-	}
+  . = ALIGN(0x1000);
+  PROVIDE(end = .);
 }
diff --git a/main.c b/main.c
index 3127b15..04e822a 100644
--- a/main.c
+++ b/main.c
@@ -1,105 +1,28 @@
 #include "types.h"
-#include "defs.h"
 #include "param.h"
 #include "memlayout.h"
-#include "mmu.h"
-#include "proc.h"
-#include "x86.h"
-
-extern pde_t *kpgdir;
-extern char end[]; // first address after kernel loaded from ELF file
-
-static void mpmain(void)  __attribute__((noreturn));
-static void startothers(void);
-
+#include "riscv.h"
+#include "defs.h"
 
 // Bootstrap processor starts running C code here.
 // Allocate a real stack and switch to it, first
 // doing some setup required for memory allocator to work.
-int
-main(uint64 mbmagic, uint64 mbaddr)
+void
+main()
 {
-  if(mbmagic != 0x2badb002)
-       panic("multiboot header not found");
-
-  kinit1(end, P2V(4*1024*1024)); // phys page allocator
-  kvmalloc();      // kernel page table
-  mpinit();        // detect other processors
-  lapicinit();     // interrupt controller
-  seginit();       // segment descriptors
-  picinit();       // disable pic
-  ioapicinit();    // another interrupt controller
-  consoleinit();   // console hardware
   uartinit();      // serial port
-  pinit();         // process table
-  tvinit();        // trap vectors
+  consoleinit();
+  printf("entering main()\n");
+  kinit();         // physical page allocator
+  kvminit();       // kernel page table
+  procinit();      // process table
+  trapinit();      // trap vectors
+#if 0
   binit();         // buffer cache
   fileinit();      // file table
   ideinit();       // disk
-  
-  startothers();   // start other processors
- 
-  kinit2(P2V(4*1024*1024), P2V(PHYSTOP)); // must come after startothers()
+#endif
   userinit();      // first user process
-  mpmain();        
-  return 0;
+
+  scheduler();        
 }
-
-extern struct cpu* getmycpu();
-
-// Common CPU setup code.
-static void
-mpmain(void)
-{
-  cprintf("cpu%d: starting %d\n", cpuid(), cpuid());
-  idtinit();       // load idt register
-  xchg(&(mycpu()->started), 1); // tell startothers() we're up
-  scheduler();     // start running processes
-}
-
-// AP processors jump here from entryother.S.
-void
-apmain(void)
-{
-  switchkvm();
-  seginit();
-  lapicinit();
-  mpmain();
-}
-
-void apstart(void);
-
-// Start the non-boot (AP) processors.
-static void
-startothers(void)
-{
-  extern uchar _binary_entryother_start[], _binary_entryother_size[];
-  uchar *code;
-  struct cpu *c;
-  char *stack;
-
-  // Write entry code to unused memory at 0x7000.
-  // The linker has placed the image of entryother.S in
-  // _binary_entryother_start.
-  code = P2V(0x7000);
-  memmove(code, _binary_entryother_start, (uint64)_binary_entryother_size);
-
-  for(c = cpus; c < cpus+ncpu; c++){
-    if(c == mycpu())  // We've started already.
-      continue;
-
-    // Tell entryother.S what stack to use, where to enter, and what
-    // pgdir to use. We cannot use kpgdir yet, because the AP processor
-    // is running in low  memory, so we use entrypgdir for the APs too.
-    stack = kalloc();
-    *(uint32*)(code-4) = V2P(apstart);
-    *(uint64*)(code-12) = (uint64) (stack+KSTACKSIZE);
-
-    lapicstartap(c->apicid, V2P(code));
-
-    // wait for cpu to finish mpmain()
-    while(c->started == 0)
-      ;
-  }
-}
-
diff --git a/memlayout.h b/memlayout.h
index 87818d3..798621e 100644
--- a/memlayout.h
+++ b/memlayout.h
@@ -1,16 +1,25 @@
-// Memory layout
+// Physical memory layout
 
-#define EXTMEM  0x100000            // Start of extended memory
-#define PHYSTOP 0xE000000           // Top physical memory
-#define DEVSPACE 0xFE000000         // Other devices are top of 32-bit address space
-#define DEVSPACETOP 0x100000000
+// qemu -machine virt is set up like this:
+// 00001000 -- boot ROM, provided by qemu
+// 10000000 -- uart0 registers
+// 80000000 -- boot ROM jumps here in machine mode
+// unused RAM after 80000000.
 
-// Key addresses for address space layout (see kmap in vm.c for layout)
-#define KERNBASE  0xFFFFFF0000000000  // First kernel virtual address
-#define KERNLINK (KERNBASE+EXTMEM)  // Address where kernel is linked
+// the kernel uses physical memory thus:
+// 80000000 -- entry.S, then kernel text and data
+// end -- start of kernel page allocation area
+// PHYSTOP -- end RAM used by the kernel
 
-#define V2P(a) (((uint64) (a)) - KERNBASE)
-#define P2V(a) ((void *)(((char *) (a)) + KERNBASE))
+// registers start here in physical memory.
+#define UART0 0x10000000L
 
-#define V2P_WO(x) ((x) - KERNBASE)    // same as V2P, but without casts
-#define P2V_WO(x) ((x) + KERNBASE)    // same as P2V, but without casts
+// the kernel expects there to be RAM
+// for use by the kernel and user pages
+// from physical address 0x80000000 to PHYSTOP.
+#define KERNBASE 0x80000000L
+#define PHYSTOP (KERNBASE + 64*1024*1024)
+
+// map the trampoline page to the highest address,
+// in both user and kernel space.
+#define TRAMPOLINE (MAXVA - PGSIZE)
diff --git a/mmu.h b/mmu.h
deleted file mode 100644
index c8b45fc..0000000
--- a/mmu.h
+++ /dev/null
@@ -1,160 +0,0 @@
-// This file contains definitions for the
-// x86 memory management unit (MMU).
-
-// Eflags register
-#define FL_TF           0x00000100      // Trap Flag
-#define FL_IF           0x00000200      // Interrupt Enable
-
-
-// Control Register flags
-#define CR0_PE          0x00000001      // Protection Enable
-#define CR0_WP          0x00010000      // Write Protect
-#define CR0_PG          0x80000000      // Paging
-
-#define CR4_PSE         0x00000010      // Page size extension
-
-// Segment selectors (indexes) in our GDTs.
-// Defined by our convention, not the architecture.
-#define SEG_KCODE32 (1<<3)  // kernel 32-bit code segment
-#define SEG_KCODE   (2<<3)  // kernel code segment
-#define SEG_KDATA   (3<<3)  // kernel data segment
-#define SEG_TSS     (4<<3)  // tss segment - takes two slots
-#define SEG_UDATA   (6<<3)  // user data segment
-#define SEG_UCODE   (7<<3)  // user code segment
-
-#define NSEGS 8
-
-#ifndef __ASSEMBLER__
-struct segdesc {
-	uint16 limit0;
-	uint16 base0;
-	uint8 base1;
-	uint8 bits;
-	uint8 bitslimit1;
-	uint8 base2;
-};
-
-// SEGDESC constructs a segment descriptor literal
-// with the given, base, limit, and type bits.
-#define SEGDESC(base, limit, bits) (struct segdesc){ \
-	(limit)&0xffff, (base)&0xffff, \
-	((base)>>16)&0xff, \
-	(bits)&0xff, \
-	(((bits)>>4)&0xf0) | ((limit>>16)&0xf), \
-	((base)>>24)&0xff, \
-}
-
-// SEGDESCHI constructs an extension segment descriptor
-// literal that records the high bits of base.
-#define SEGDESCHI(base) (struct segdesc) {                        \
-  (((base)>>32)&0xffff), (((base)>>48)&0xffff), \
-}
-
-#endif
-
-#define DPL_USER    0x3     // User DPL
-
-#define SEG_A      (1<<0)      // segment accessed bit 
-#define SEG_R      (1<<1)      // readable (code) 
-#define SEG_W      (1<<1)      // writable (data) 
-#define SEG_C      (1<<2)      // conforming segment (code) 
-#define SEG_E      (1<<2)      // expand-down bit (data) 
-#define SEG_CODE   (1<<3)      // code segment (instead of data) 
-
-// User and system segment bits.
-#define SEG_S      (1<<4)      // if 0, system descriptor 
-#define SEG_DPL(x) ((x)<<5)    // descriptor privilege level (2 bits) 
-#define SEG_P      (1<<7)      // segment present 
-#define SEG_AVL    (1<<8)      // available for operating system use 
-#define SEG_L      (1<<9)      // long mode 
-#define SEG_D      (1<<10)     // default operation size 32-bit 
-#define SEG_G      (1<<11)     // granularity 
-
-// Application segment type bits
-#define STA_X       0x8     // Executable segment
-#define STA_W       0x2     // Writeable (non-executable segments)
-#define STA_R       0x2     // Readable (executable segments)
-
-// System segment type bits
-#define SEG_LDT    (2<<0)      // local descriptor table 
-#define SEG_TSS64A (9<<0)      // available 64-bit TSS 
-#define SEG_TSS64B (11<<0)     // busy 64-bit TSS 
-#define SEG_CALL64 (12<<0)     // 64-bit call gate 
-#define SEG_INTR64 (14<<0)     // 64-bit interrupt gate 
-#define SEG_TRAP64 (15<<0)     // 64-bit trap gate 
-
-// A virtual address 'la' has a six-part structure as follows:
-//
-// +--16--+---9---+------9-------+-----9----+----9-------+----12-------+
-// | Sign | PML4  |Page Directory| Page Dir |Page Table  | Offset Page |
-// |Extend| Index | Pointer Index|  Index   |  Index     | in Page     |
-// +------+-------+--------------+----------+------------+-------------+
-//         L3 pgtab   L2 pgtab      L1 pgtab   L0 pgtab
-
-// Page directory and page table constants.
-#define NPDENTRIES      512     // # directory entries per page directory
-#define PGSIZE          4096    // bytes mapped by a page
-#define PGSHIFT         12      // offset of PTX in a linear address
-
-#define PXMASK          0x1FF
-#define PXSHIFT(n)	(PGSHIFT+(9*(n)))  // shift for index into level n page table
-#define PX(n, va)	((((uint64) (va)) >> PXSHIFT(n)) & PXMASK)
-#define L_PML4           3
-    
-#define PGROUNDUP(sz)  (((sz)+PGSIZE-1) & ~(PGSIZE-1))
-#define PGROUNDDOWN(a) (((a)) & ~(PGSIZE-1))
-
-// Page table/directory entry flags.
-#define PTE_P           0x001   // Present
-#define PTE_W           0x002   // Writeable
-#define PTE_U           0x004   // User
-#define PTE_PS          0x080   // Page Size
-#define PTE_PWT         0x008   // Write-Through
-#define PTE_PCD         0x010   // Cache-Disable
-
-// Address in page table or page directory entry
-#define PTE_ADDR(pte)   ((uint64)(pte) & ~0xFFF)
-#define PTE_FLAGS(pte)  ((uint64)(pte) &  0xFFF)
-
-#ifndef __ASSEMBLER__
-
-typedef uint64 pte_t;
-
-struct taskstate {
-  uint8 reserved0[4];
-  uint64 rsp[3];
-  uint64 ist[8];
-  uint8 reserved1[10];
-  uint16 iomba;
-  uint8 iopb[0];
-} __attribute__ ((packed));
-
-#define INT_P      (1<<7)      // interrupt descriptor present
-
-struct intgate
-{
-	uint16 rip0;
-	uint16 cs;
-	uint8 reserved0;
-	uint8 bits;
-	uint16 rip1;
-	uint32 rip2;
-	uint32 reserved1;
-};
-
-// INTDESC constructs an interrupt descriptor literal
-// that records the given code segment, instruction pointer,
-// and type bits.
-#define INTDESC(cs, rip, bits) (struct intgate){ \
-	(rip)&0xffff, (cs), 0, bits, ((rip)>>16)&0xffff, \
-	(uint64)(rip)>>32, 0, \
-}
-
-// See section 4.6 of amd64 vol2
-struct desctr
-{
-  uint16 limit;
-  uint64 base;
-} __attribute__((packed, aligned(16)));   // important!
-
-#endif
diff --git a/msr.h b/msr.h
deleted file mode 100644
index ad901a6..0000000
--- a/msr.h
+++ /dev/null
@@ -1,25 +0,0 @@
-// SYSCALL and SYSRET registers
-#define MSR_STAR        0xc0000081
-#define MSR_LSTAR       0xc0000082
-#define MSR_CSTAR       0xc0000083
-#define MSR_SFMASK      0xc0000084
-
-// GS
-#define MSR_GS_BASE     0xc0000101
-#define MSR_GS_KERNBASE 0xc0000102
-
-static inline uint64
-readmsr(uint32 msr)
-{
-  uint32 hi, lo;
-  __asm volatile("rdmsr" : "=d" (hi), "=a" (lo) : "c" (msr));
-  return ((uint64) lo) | (((uint64) hi) << 32);
-}
-
-static inline void
-writemsr(uint64 msr, uint64 val)
-{
-  uint32 lo = val & 0xffffffff;
-  uint32 hi = val >> 32;
-  __asm volatile("wrmsr" : : "c" (msr), "a" (lo), "d" (hi) : "memory");
-}
diff --git a/param.h b/param.h
index a7e90ef..24f8c8f 100644
--- a/param.h
+++ b/param.h
@@ -1,5 +1,4 @@
 #define NPROC        64  // maximum number of processes
-#define KSTACKSIZE 4096  // size of per-process kernel stack
 #define NCPU          8  // maximum number of CPUs
 #define NOFILE       16  // open files per process
 #define NFILE       100  // open files per system
diff --git a/proc.c b/proc.c
index 3c0acbd..e574db0 100644
--- a/proc.c
+++ b/proc.c
@@ -1,18 +1,20 @@
 #include "types.h"
-#include "defs.h"
 #include "param.h"
 #include "memlayout.h"
-#include "mmu.h"
-#include "x86.h"
+#include "riscv.h"
 #include "proc.h"
 #include "spinlock.h"
+#include "defs.h"
 
 struct {
   struct spinlock lock;
   struct proc proc[NPROC];
 } ptable;
 
-static struct proc *initproc;
+// XXX riscv move somewhere else
+struct cpu cpus[NCPU];
+
+struct proc *initproc;
 
 int nextpid = 1;
 extern void forkret(void);
@@ -22,57 +24,36 @@ extern void sysexit(void);
 
 static void wakeup1(void *chan);
 
+extern char trampstart[]; // trampoline.S
+
 void
-pinit(void)
+procinit(void)
 {
   initlock(&ptable.lock, "ptable");
 }
 
-// Must be called with interrupts disabled
+// Must be called with interrupts disabled.
+// XXX riscv
 int
 cpuid() {
-  return mycpu()-cpus;
+  return 0;
 }
 
-// Must be called with interrupts disabled to avoid the caller being
-// rescheduled between reading lapicid and running through the loop.
-struct cpu*
-getmycpu(void)
-{
-  int apicid, i;
-  
-  if(readeflags()&FL_IF)
-    panic("getmycpu called with interrupts enabled\n");
-  
-  apicid = lapicid();
-  // APIC IDs are not guaranteed to be contiguous.
-  for (i = 0; i < ncpu; ++i) {
-    if (cpus[i].apicid == apicid)
-      return &cpus[i];
-  }
-  panic("unknown apicid\n");
-}
-
-// Return this core's cpu struct using %gs. %gs points this core's struct
-// cpu. Offet 24 in struct cpu is cpu.
+// Return this core's cpu struct.
+// XXX riscv
 struct cpu*
 mycpu(void) {
   struct cpu *c;
-  asm volatile("mov %%gs:24, %0" : "=r" (c));
+  c = &cpus[0];
   return c;
 }
 
 // Disable interrupts so that we are not rescheduled
 // while reading proc from the cpu structure
+// XXX riscv
 struct proc*
 myproc(void) {
-  struct cpu *c;
-  struct proc *p;
-  pushcli();
-  c = mycpu();
-  p = c->proc;
-  popcli();
-  return p;
+  return cpus[0].proc;
 }
 
 //PAGEBREAK: 32
@@ -84,7 +65,6 @@ static struct proc*
 allocproc(void)
 {
   struct proc *p;
-  char *sp;
 
   acquire(&ptable.lock);
 
@@ -101,56 +81,73 @@ found:
 
   release(&ptable.lock);
 
-  // Allocate kernel stack.
+  // Allocate a page for the kernel stack.
   if((p->kstack = kalloc()) == 0){
     p->state = UNUSED;
     return 0;
   }
-  sp = p->kstack + KSTACKSIZE;
 
-  // Leave room for syscall frame.
-  sp -= sizeof *p->sf;
+  // Allocate a trapframe page.
+  if((p->tf = (struct trapframe *)kalloc()) == 0){
+    p->state = UNUSED;
+    return 0;
+  }
 
-  if ((uint64) sp % 16)
-    panic("misaligned sp");
+  // An empty user page table.
+  p->pagetable = uvmcreate();
 
-  p->sf = (struct sysframe*)sp;
+  // 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,
+           (uint64)trampstart, PTE_R | PTE_X);
+
+  // map the trapframe, for trampoline.S.
+  mappages(p->pagetable, (TRAMPOLINE - PGSIZE), PGSIZE,
+           (uint64)(p->tf), PTE_R | PTE_W);
 
   // Set up new context to start executing at forkret,
-  // which returns to sysexit.
-  sp -= sizeof(uint64);
-  *(uint64*)sp = (uint64)sysexit;
-
-  sp -= sizeof *p->context;
-  p->context = (struct context*)sp;
-  memset(p->context, 0, sizeof *p->context);
-  p->context->rip = (uint64)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;
 }
 
+// XXX hack because I don't know how to incorporate initcode
+// into the kernel binary. just the exec system call, no arguments.
+// manually copied from initcode.asm.
+unsigned char initcode[] = {
+  0x85, 0x48,             // li a7, 1 -- SYS_fork
+  0x73, 0x00, 0x00, 0x00, // ecall
+  0x8d, 0x48,             // li a7, 3 -- SYS_wait
+  0x73, 0x00, 0x00, 0x00, // ecall
+  0x89, 0x48,             // li a7, 2 -- SYS_exit
+  0x73, 0x00, 0x00, 0x00, // ecall
+};
+
 //PAGEBREAK: 32
 // Set up first user process.
 void
 userinit(void)
 {
   struct proc *p;
-  extern char _binary_initcode_start[], _binary_initcode_size[];
 
   p = allocproc();
-  
   initproc = p;
-  if((p->pgdir = setupkvm()) == 0)
-    panic("userinit: out of memory?");
-  inituvm(p->pgdir, _binary_initcode_start, (uint64)_binary_initcode_size);
+  
+  uvminit(p->pagetable, initcode, sizeof(initcode));
   p->sz = PGSIZE;
-  memset(p->sf, 0, sizeof(*p->sf));
-  p->sf->r11 = FL_IF;
-  p->sf->rsp = PGSIZE;
-  p->sf->rcx = 0;  // beginning of initcode.S
+
+  // prepare for the very first kernel->user.
+  p->tf->epc = 0;
+  p->tf->sp = PGSIZE;
 
   safestrcpy(p->name, "initcode", sizeof(p->name));
-  p->cwd = namei("/");
+  // XXX riscv
+  //p->cwd = namei("/");
 
   // this assignment to p->state lets other cores
   // run this process. the acquire forces the above
@@ -163,62 +160,65 @@ userinit(void)
   release(&ptable.lock);
 }
 
+#if 0
+
 // Grow current process's memory by n bytes.
 // Return 0 on success, -1 on failure.
 int
 growproc(int n)
 {
   uint sz;
-  struct proc *curproc = myproc();
+  struct proc *p = myproc();
 
-  sz = curproc->sz;
+  sz = p->sz;
   if(n > 0){
-    if((sz = allocuvm(curproc->pgdir, sz, sz + n)) == 0)
+    if((sz = allocuvm(p->pagetable, sz, sz + n)) == 0)
       return -1;
   } else if(n < 0){
-    if((sz = deallocuvm(curproc->pgdir, sz, sz + n)) == 0)
+    if((sz = uvmdealloc(p->pagetable, sz, sz + n)) == 0)
       return -1;
   }
-  curproc->sz = sz;
-  switchuvm(curproc);
+  p->sz = sz;
+  switchuvm(p);
   return 0;
 }
+#endif
 
-// Create a new process copying p as the parent.
-// Sets up stack to return as if from system call.
-// Caller must set state of returned proc to RUNNABLE.
+// Create a new process, copying p as the parent.
+// Sets up child kernel stack to return as if from system call.
 int
 fork(void)
 {
   int i, pid;
   struct proc *np;
-  struct proc *curproc = myproc();
+  struct proc *p = myproc();
 
   // Allocate process.
   if((np = allocproc()) == 0){
     return -1;
   }
 
-  // Copy process state from proc.
-  if((np->pgdir = copyuvm(curproc->pgdir, curproc->sz)) == 0){
-    kfree(np->kstack);
-    np->kstack = 0;
-    np->state = UNUSED;
-    return -1;
-  }
-  np->sz = curproc->sz;
-  np->parent = curproc;
-  *np->sf = *curproc->sf;
+  // Copy user memory from parent to child.
+  uvmcopy(p->pagetable, np->pagetable, p->sz);
+  np->sz = p->sz;
 
-  // Clear %eax so that fork returns 0 in the child.
-  np->sf->rax = 0;
+  np->parent = p;
 
+  // copy saved user registers.
+  *(np->tf) = *(p->tf);
+
+  // Cause fork to return 0 in the child.
+  np->tf->a0 = 0;
+
+#if 0 // XXX riscv
+  // increment reference counts on open file descriptors.
   for(i = 0; i < NOFILE; i++)
-    if(curproc->ofile[i])
-      np->ofile[i] = filedup(curproc->ofile[i]);
-  np->cwd = idup(curproc->cwd);
+    if(p->ofile[i])
+      np->ofile[i] = filedup(p->ofile[i]);
+  np->cwd = idup(p->cwd);
+#endif
 
-  safestrcpy(np->name, curproc->name, sizeof(curproc->name));
+  safestrcpy(np->name, p->name, sizeof(p->name));
 
   pid = np->pid;
 
@@ -233,46 +233,48 @@ fork(void)
 
 // Exit the current process.  Does not return.
 // An exited process remains in the zombie state
-// until its parent calls wait() to find out it exited.
+// until its parent calls wait().
 void
 exit(void)
 {
-  struct proc *curproc = myproc();
-  struct proc *p;
+  struct proc *p = myproc();
+  struct proc *pp;
   int fd;
 
-  if(curproc == initproc)
+  if(p == initproc)
     panic("init exiting");
 
+#if 0 // XXX riscv
   // Close all open files.
   for(fd = 0; fd < NOFILE; fd++){
-    if(curproc->ofile[fd]){
-      fileclose(curproc->ofile[fd]);
-      curproc->ofile[fd] = 0;
+    if(p->ofile[fd]){
+      fileclose(p->ofile[fd]);
+      p->ofile[fd] = 0;
     }
   }
 
   begin_op();
-  iput(curproc->cwd);
+  iput(p->cwd);
   end_op();
-  curproc->cwd = 0;
+#endif
+  p->cwd = 0;
 
   acquire(&ptable.lock);
 
   // Parent might be sleeping in wait().
-  wakeup1(curproc->parent);
+  wakeup1(p->parent);
 
   // Pass abandoned children to init.
-  for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
-    if(p->parent == curproc){
-      p->parent = initproc;
-      if(p->state == ZOMBIE)
+  for(pp = ptable.proc; pp < &ptable.proc[NPROC]; pp++){
+    if(pp->parent == p){
+      pp->parent = initproc;
+      if(pp->state == ZOMBIE)
         wakeup1(initproc);
     }
   }
 
   // Jump into the scheduler, never to return.
-  curproc->state = ZOMBIE;
+  p->state = ZOMBIE;
   sched();
   panic("zombie exit");
 }
@@ -282,42 +284,47 @@ exit(void)
 int
 wait(void)
 {
-  struct proc *p;
+  struct proc *np;
   int havekids, pid;
-  struct proc *curproc = myproc();
+  struct proc *p = myproc();
   
   acquire(&ptable.lock);
   for(;;){
     // Scan through table looking for exited children.
     havekids = 0;
-    for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
-      if(p->parent != curproc)
+    for(np = ptable.proc; np < &ptable.proc[NPROC]; np++){
+      if(np->parent != p)
         continue;
       havekids = 1;
-      if(p->state == ZOMBIE){
+      if(np->state == ZOMBIE){
         // Found one.
-        pid = p->pid;
-        kfree(p->kstack);
-        p->kstack = 0;
-        freevm(p->pgdir, p->sz);
-         p->pid = 0;
-        p->parent = 0;
-        p->name[0] = 0;
-        p->killed = 0;
-        p->state = UNUSED;
+        pid = np->pid;
+        kfree(np->kstack);
+        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);
+        np->pagetable = 0;
+        np->pid = 0;
+        np->parent = 0;
+        np->name[0] = 0;
+        np->killed = 0;
+        np->state = UNUSED;
         release(&ptable.lock);
         return pid;
       }
     }
 
     // No point waiting if we don't have any children.
-    if(!havekids || curproc->killed){
+    if(!havekids || p->killed){
       release(&ptable.lock);
       return -1;
     }
 
     // Wait for children to exit.  (See wakeup1 call in proc_exit.)
-    sleep(curproc, &ptable.lock);  //DOC: wait-sleep
+    sleep(p, &ptable.lock);  //DOC: wait-sleep
   }
 }
 
@@ -338,7 +345,8 @@ scheduler(void)
   c->proc = 0;
   for(;;){
     // Enable interrupts on this processor.
-    sti();
+    // XXX riscv
+    //sti();
     
     // Loop over process table looking for process to run.
     acquire(&ptable.lock);
@@ -350,11 +358,11 @@ scheduler(void)
       // to release ptable.lock and then reacquire it
       // before jumping back to us.
       c->proc = p;
-      switchuvm(p);
       p->state = RUNNING;
 
-      swtch(&(c->scheduler), p->context);
-      switchkvm();
+      printf("switch...\n");
+      swtch(&c->scheduler, &p->context);
+      printf("switch returned\n");
 
       // Process is done running for now.
       // It should have changed its p->state before coming back.
@@ -380,14 +388,10 @@ sched(void)
 
   if(!holding(&ptable.lock))
     panic("sched ptable.lock");
-  if(mycpu()->ncli != 1)
-    panic("sched locks");
   if(p->state == RUNNING)
     panic("sched running");
-  if(readeflags()&FL_IF)
-    panic("sched interruptible");
   intena = mycpu()->intena;
-  swtch(&p->context, mycpu()->scheduler);
+  swtch(&p->context, &mycpu()->scheduler);
   mycpu()->intena = intena;
 }
 
@@ -402,24 +406,29 @@ yield(void)
 }
 
 // A fork child's very first scheduling by scheduler()
-// will swtch here.  "Return" to user space.
+// will swtch to forkret.
 void
 forkret(void)
 {
+  struct proc *p = myproc();
+
   static int first = 1;
   // Still holding ptable.lock from scheduler.
   release(&ptable.lock);
 
+  printf("entering forkret\n");
+
   if (first) {
     // Some initialization functions must be run in the context
     // of a regular process (e.g., they call sleep), and thus cannot
     // be run from main().
     first = 0;
-    iinit(ROOTDEV);
-    initlog(ROOTDEV);
+    // XXX riscv
+    //iinit(ROOTDEV);
+    //initlog(ROOTDEV);
   }
-  
-  // Return to "caller", actually trapret (see allocproc).
+
+  usertrapret();
 }
 
 // Atomically release lock and sleep on chan.
@@ -483,6 +492,8 @@ wakeup(void *chan)
   release(&ptable.lock);
 }
 
+#if 0
+
 // Kill the process with the given pid.
 // Process won't exit until it returns
 // to user space (see trap in trap.c).
@@ -533,12 +544,14 @@ procdump(void)
       state = states[p->state];
     else
       state = "???";
-    cprintf("%d %s %s", p->pid, state, p->name);
+    printf("%d %s %s", p->pid, state, p->name);
     if(p->state == SLEEPING){
       getcallerpcs((uint64*)p->context->rbp+2, pc);
       for(i=0; i<10 && pc[i] != 0; i++)
-        cprintf(" %p", pc[i]);
+        printf(" %p", pc[i]);
     }
-    cprintf("\n");
+    printf("\n");
   }
 }
+
+#endif
diff --git a/proc.h b/proc.h
index 0b01b75..1e2238c 100644
--- a/proc.h
+++ b/proc.h
@@ -1,13 +1,30 @@
+// Saved registers for kernel context switches.
+struct context {
+  uint64 ra;
+  uint64 sp;
+
+  // callee-saved
+  uint64 s0;
+  uint64 s1;
+  uint64 s2;
+  uint64 s3;
+  uint64 s4;
+  uint64 s5;
+  uint64 s6;
+  uint64 s7;
+  uint64 s8;
+  uint64 s9;
+  uint64 s10;
+  uint64 s11;
+};
+
 // Per-CPU state
 struct cpu {
   uint64 syscallno;            // Temporary used by sysentry
   uint64 usp;                  // Temporary used by sysentry
   struct proc *proc;           // The process running on this cpu or null
   struct cpu *cpu;             // XXX
-  uchar apicid;                // Local APIC ID
-  struct context *scheduler;   // swtch() here to enter scheduler
-  struct taskstate ts;         // Used by x86 to find stack for interrupt
-  struct segdesc gdt[NSEGS];   // x86 global descriptor table
+  struct context scheduler;   // swtch() here to enter scheduler
   volatile uint started;       // Has the CPU started?
   int ncli;                    // Depth of pushcli nesting.
   int intena;                  // Were interrupts enabled before pushcli?
@@ -17,39 +34,52 @@ extern struct cpu cpus[NCPU];
 extern int ncpu;
 
 //PAGEBREAK: 17
-// Saved registers for kernel context switches.
-// Don't need to save all the segment registers (%cs, etc),
-// because they are constant across kernel contexts.
-// Don't need to save %eax, %ecx, %edx, because the
-// x86 convention is that the caller has saved them.
-// Contexts are stored at the bottom of the stack they
-// describe; the stack pointer is the address of the context.
-// The layout of the context matches the layout of the stack in swtch.S
-// at the "Switch stacks" comment. Switch doesn't save eip explicitly,
-// but it is on the stack and allocproc() manipulates it.
-struct context {
-  uint64 r15;
-  uint64 r14;
-  uint64 r13;
-  uint64 r12;
-  uint64 r11;
-  uint64 rbx;
-  uint64 rbp;
-  uint64 rip;
+
+// per-process data for the early trap handling code in trampoline.S.
+// sits in a page by itself just under the trampoline page in the
+// user page table. not specially mapped in the kernel page table.
+// the sscratch register points here.
+// trampoline.S saves user registers, then restores kernel_sp and
+// kernel_satp.
+// no need to save s0-s11 (callee-saved) since C code and swtch() save them.
+struct trapframe {
+  /*   0 */ uint64 kernel_satp;
+  /*   8 */ uint64 kernel_sp;
+  /*  16 */ uint64 kernel_trap; // address of trap()
+  /*  24 */ uint64 epc; // saved user program counter
+  /*  32 */ uint64 ra;
+  /*  40 */ uint64 sp;
+  /*  48 */ uint64 gp;
+  /*  56 */ uint64 tp;
+  /*  64 */ uint64 t0;
+  /*  72 */ uint64 t1;
+  /*  80 */ uint64 t2;
+  /*  88 */ uint64 a0;
+  /*  96 */ uint64 a1;
+  /* 104 */ uint64 a2;
+  /* 112 */ uint64 a3;
+  /* 120 */ uint64 a4;
+  /* 128 */ uint64 a5;
+  /* 136 */ uint64 a6;
+  /* 144 */ uint64 a7;
+  /* 152 */ uint64 t3;
+  /* 160 */ uint64 t4;
+  /* 168 */ uint64 t5;
+  /* 176 */ uint64 t6;
 };
 
 enum procstate { UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };
 
 // Per-process state
 struct proc {
-  char *kstack;                // Bottom of kernel stack for this process, must be first entry
+  char *kstack;                // Bottom of kernel stack for this process
   uint64 sz;                   // Size of process memory (bytes)
-  pde_t* pgdir;                // Page table
+  pagetable_t pagetable;       // Page table
   enum procstate state;        // Process state
   int pid;                     // Process ID
   struct proc *parent;         // Parent process
-  struct sysframe *sf;         // Syscall frame for current syscall
-  struct context *context;     // swtch() here to run process
+  struct trapframe *tf;        // data page for trampoline.S
+  struct context context;      // swtch() here to run process
   void *chan;                  // If non-zero, sleeping on chan
   int killed;                  // If non-zero, have been killed
   struct file *ofile[NOFILE];  // Open files
diff --git a/riscv.h b/riscv.h
new file mode 100644
index 0000000..92fa6e3
--- /dev/null
+++ b/riscv.h
@@ -0,0 +1,172 @@
+// Machine Status Register, mstatus
+
+#define MSTATUS_MPP_MASK (3L << 11)
+#define MSTATUS_MPP_M (3L << 11)
+#define MSTATUS_MPP_S (1L << 11)
+#define MSTATUS_MPP_U (0L << 11)
+
+static inline uint64
+r_mstatus()
+{
+  uint64 x;
+  asm("csrr %0, mstatus" : "=r" (x) );
+  return x;
+}
+
+static inline void 
+w_mstatus(uint64 x)
+{
+  asm("csrw mstatus, %0" : : "r" (x));
+}
+
+// machine exception program counter, holds the
+// instruction address to which a return from
+// exception will go.
+static inline void 
+w_mepc(uint64 x)
+{
+  asm("csrw mepc, %0" : : "r" (x));
+}
+
+// Supervisor Status Register, sstatus
+
+#define SSTATUS_SPP (1L << 8) // 1=Supervisor, 0=User
+
+static inline uint64
+r_sstatus()
+{
+  uint64 x;
+  asm("csrr %0, sstatus" : "=r" (x) );
+  return x;
+}
+
+static inline void 
+w_sstatus(uint64 x)
+{
+  asm("csrw sstatus, %0" : : "r" (x));
+}
+
+// machine exception program counter, holds the
+// instruction address to which a return from
+// exception will go.
+static inline void 
+w_sepc(uint64 x)
+{
+  asm("csrw sepc, %0" : : "r" (x));
+}
+
+static inline uint64
+r_sepc()
+{
+  uint64 x;
+  asm("csrr %0, sepc" : "=r" (x) );
+  return x;
+}
+
+// Machine Exception Delegation
+static inline uint64
+r_medeleg()
+{
+  uint64 x;
+  asm("csrr %0, medeleg" : "=r" (x) );
+  return x;
+}
+
+static inline void 
+w_medeleg(uint64 x)
+{
+  asm("csrw medeleg, %0" : : "r" (x));
+}
+
+// Machine Interrupt Delegation
+static inline uint64
+r_mideleg()
+{
+  uint64 x;
+  asm("csrr %0, mideleg" : "=r" (x) );
+  return x;
+}
+
+static inline void 
+w_mideleg(uint64 x)
+{
+  asm("csrw mideleg, %0" : : "r" (x));
+}
+
+// Supervisor Trap-Vector Base Address
+// low two bits are mode.
+static inline void 
+w_stvec(uint64 x)
+{
+  asm("csrw stvec, %0" : : "r" (x));
+}
+
+// use riscv's sv39 page table scheme.
+#define SATP_SV39 (8L << 60)
+
+#define MAKE_SATP(pagetable) (SATP_SV39 | (((uint64)pagetable) >> 12))
+
+// supervisor address translation and protection;
+// holds the address of the page table.
+static inline void 
+w_satp(uint64 x)
+{
+  asm("csrw satp, %0" : : "r" (x));
+}
+
+static inline uint64
+r_satp()
+{
+  uint64 x;
+  asm("csrr %0, satp" : "=r" (x) );
+  return x;
+}
+
+// Supervisor Scratch register, for early trap handler in trampoline.S.
+static inline void 
+w_sscratch(uint64 x)
+{
+  asm("csrw sscratch, %0" : : "r" (x));
+}
+
+// Supervisor trap cause
+static inline uint64
+r_scause()
+{
+  uint64 x;
+  asm("csrr %0, scause" : "=r" (x) );
+  return x;
+}
+
+#define PGSIZE 4096 // bytes per page
+#define PGSHIFT 12  // bits of offset within a page
+
+#define PGROUNDUP(sz)  (((sz)+PGSIZE-1) & ~(PGSIZE-1))
+#define PGROUNDDOWN(a) (((a)) & ~(PGSIZE-1))
+
+#define PTE_V (1L << 0) // valid
+#define PTE_R (1L << 1)
+#define PTE_W (1L << 2)
+#define PTE_X (1L << 3)
+#define PTE_U (1L << 4) // 1 -> user can access
+
+// shift a physical address to the right place for a PTE.
+#define PA2PTE(pa) ((((uint64)pa) >> 12) << 10)
+
+#define PTE2PA(pte) (((pte) >> 10) << 12)
+
+#define PTE_FLAGS(pte) ((pte) & (PTE_V|PTE_R|PTE_W|PTE_X|PTE_U))
+
+// extract the three 9-bit page table indices from a virtual address.
+#define PXMASK          0x1FF // 9 bits
+#define PXSHIFT(level)  (PGSHIFT+(9*(level)))
+#define PX(level, va) ((((uint64) (va)) >> PXSHIFT(level)) & PXMASK)
+
+// one beyond the highest possible virtual address.
+// MAXVA is actually one bit less than the max allowed by
+// Sv39, to avoid having to sign-extend virtual addresses
+// that have the high bit set.
+#define MAXVA (1L << (9 + 9 + 9 + 12 - 1))
+
+typedef uint64 pte_t;
+typedef uint64 *pagetable_t; // 512 PTEs
diff --git a/spinlock.c b/spinlock.c
index 9ee65f6..0377870 100644
--- a/spinlock.c
+++ b/spinlock.c
@@ -1,13 +1,11 @@
 // Mutual exclusion spin locks.
 
 #include "types.h"
-#include "defs.h"
 #include "param.h"
-#include "x86.h"
 #include "memlayout.h"
-#include "mmu.h"
-#include "proc.h"
 #include "spinlock.h"
+#include "riscv.h"
+#include "defs.h"
 
 void
 initlock(struct spinlock *lk, char *name)
@@ -17,6 +15,27 @@ initlock(struct spinlock *lk, char *name)
   lk->cpu = 0;
 }
 
+void
+acquire(struct spinlock *lk)
+{
+  lk->locked = 1;
+  lk->cpu = mycpu();
+}
+
+void
+release(struct spinlock *lk)
+{
+  lk->locked = 0;
+  lk->cpu = 0;
+}
+
+int
+holding(struct spinlock *lk)
+{
+  return lk->locked && lk->cpu == mycpu();
+}
+
+#if 0
 // Acquire the lock.
 // Loops (spins) until the lock is acquired.
 // Holding a lock for a long time may cause
@@ -37,7 +56,7 @@ acquire(struct spinlock *lk)
   // references happen after the lock is acquired.
   __sync_synchronize();
 
-  // Record info about lock acquisition for debugging.
+  // Record info about lock acquisition for holding() and debugging.
   lk->cpu = mycpu();
   getcallerpcs(&lk, lk->pcs);
 }
@@ -87,11 +106,11 @@ getcallerpcs(void *v, uint64 pcs[])
 
 // Check whether this cpu is holding the lock.
 int
-holding(struct spinlock *lock)
+holding(struct spinlock *lk)
 {
   int r;
   pushcli();
-  r = lock->locked && lock->cpu == mycpu();
+  r = lk->locked && lk->cpu == mycpu();
   popcli();
   return r;
 }
@@ -123,4 +142,4 @@ popcli(void)
   if(mycpu()->ncli == 0 && mycpu()->intena)
     sti();
 }
-
+#endif
diff --git a/start.c b/start.c
new file mode 100644
index 0000000..5167ab4
--- /dev/null
+++ b/start.c
@@ -0,0 +1,34 @@
+#include "types.h"
+#include "memlayout.h"
+#include "riscv.h"
+#include "defs.h"
+
+void main();
+
+// entry.S uses this as the initial stack.
+char stack0[4096];
+
+// entry.S jumps here in machine mode on stack0.
+void
+mstart()
+{
+  // set M Previous Privilege mode to Supervisor, for mret.
+  unsigned long x = r_mstatus();
+  x &= ~MSTATUS_MPP_MASK;
+  x |= MSTATUS_MPP_S;
+  w_mstatus(x);
+
+  // set M Exception Program Counter to main, for mret.
+  // requires gcc -mcmodel=medany
+  w_mepc((uint64)main);
+
+  // disable paging for now.
+  w_satp(0);
+
+  // delegate all interrupts and exceptions to supervisor mode.
+  w_medeleg(0xffff);
+  w_mideleg(0xffff);
+  
+  // jump to main in supervisor mode.
+  asm("mret");
+}
diff --git a/string.c b/string.c
index 861ea25..d99e612 100644
--- a/string.c
+++ b/string.c
@@ -1,14 +1,13 @@
 #include "types.h"
-#include "x86.h"
 
 void*
 memset(void *dst, int c, uint n)
 {
-  if ((uint64)dst%4 == 0 && n%4 == 0){
-    c &= 0xFF;
-    stosl(dst, (c<<24)|(c<<16)|(c<<8)|c, n/4);
-  } else
-    stosb(dst, c, n);
+  char *cdst = (char *) dst;
+  int i;
+  for(i = 0; i < n; i++){
+    cdst[i] = c;
+  }
   return dst;
 }
 
diff --git a/swtch.S b/swtch.S
index aa527d8..17a8663 100644
--- a/swtch.S
+++ b/swtch.S
@@ -1,35 +1,42 @@
 # Context switch
 #
-#   void swtch(struct context **old, struct context *new);
+#   void swtch(struct context *old, struct context *new);
 # 
-# Save the current registers on the stack, creating
-# a struct context, and save its address in *old.
-# Switch stacks to new and pop previously-saved registers.
+# Save current registers in old. Load from new.	
+
 
 .globl swtch
 swtch:
-  # Save old callee-saved registers
-  push %rbp
-  push %rbx
-  push %r11
-  push %r12
-  push %r13
-  push %r14
-  push %r15
+        sd ra, 0(a0)
+        sd sp, 8(a0)
+        sd s0, 16(a0)
+        sd s1, 24(a0)
+        sd s2, 32(a0)
+        sd s3, 40(a0)
+        sd s4, 48(a0)
+        sd s5, 56(a0)
+        sd s6, 64(a0)
+        sd s7, 72(a0)
+        sd s8, 80(a0)
+        sd s9, 88(a0)
+        sd s10, 96(a0)
+        sd s11, 104(a0)
 
-  # Switch stacks
-  mov %rsp, (%rdi)   # first arg of swtch is in rdi
-  mov %rsi, %rsp     # second arg of swtch is in rsi
-
-  # Load new callee-saved registers
-  pop %r15
-  pop %r14
-  pop %r13
-  pop %r12
-  pop %r11
-  pop %rbx
-  pop %rbp
-
-  ret
+        ld ra, 0(a1)
+        ld sp, 8(a1)
+        ld s0, 16(a1)
+        ld s1, 24(a1)
+        ld s2, 32(a1)
+        ld s3, 40(a1)
+        ld s4, 48(a1)
+        ld s5, 56(a1)
+        ld s6, 64(a1)
+        ld s7, 72(a1)
+        ld s8, 80(a1)
+        ld s9, 88(a1)
+        ld s10, 96(a1)
+        ld s11, 104(a1)
+        
+        ret
 
 	
diff --git a/syscall.c b/syscall.c
index b815f28..d3825cb 100644
--- a/syscall.c
+++ b/syscall.c
@@ -1,11 +1,10 @@
 #include "types.h"
-#include "defs.h"
 #include "param.h"
 #include "memlayout.h"
-#include "mmu.h"
+#include "riscv.h"
 #include "proc.h"
-#include "x86.h"
 #include "syscall.h"
+#include "defs.h"
 
 // User code makes a system call with INT T_SYSCALL.
 // System call number in %eax.
@@ -17,9 +16,9 @@
 int
 fetchint(uint64 addr, int *ip)
 {
-  struct proc *curproc = myproc();
+  struct proc *p = myproc();
 
-  if(addr >= curproc->sz || addr+4 > curproc->sz)
+  if(addr >= p->sz || addr+4 > p->sz)
     return -1;
   *ip = *(uint64*)(addr);
   return 0;
@@ -29,8 +28,8 @@ fetchint(uint64 addr, int *ip)
 int
 fetchaddr(uint64 addr, uint64 *ip)
 {
-  struct proc *curproc = myproc();
-  if(addr >= curproc->sz || addr+sizeof(uint64) > curproc->sz)
+  struct proc *p = myproc();
+  if(addr >= p->sz || addr+sizeof(uint64) > p->sz)
     return -1;
   *ip = *(uint64*)(addr);
   return 0;
@@ -43,12 +42,12 @@ int
 fetchstr(uint64 addr, char **pp)
 {
   char *s, *ep;
-  struct proc *curproc = myproc();
+  struct proc *p = myproc();
 
-  if(addr >= curproc->sz)
+  if(addr >= p->sz)
     return -1;
   *pp = (char*)addr;
-  ep = (char*)curproc->sz;
+  ep = (char*)p->sz;
   for(s = *pp; s < ep; s++){
     if(*s == 0)
       return s - *pp;
@@ -59,20 +58,20 @@ fetchstr(uint64 addr, char **pp)
 static uint64
 fetcharg(int n)
 {
-  struct proc *curproc = myproc();
+  struct proc *p = myproc();
   switch (n) {
   case 0:
-    return curproc->sf->rdi;
+    return p->tf->a0;
   case 1:
-    return curproc->sf->rsi;
+    return p->tf->a1;
   case 2:
-    return curproc->sf->rdx;
+    return p->tf->a2;
   case 3:
-    return curproc->sf->r10;
+    return p->tf->a3;
   case 4:
-    return curproc->sf->r8;
+    return p->tf->a4;
   case 5:
-    return curproc->sf->r9;
+    return p->tf->a5;
   }
   panic("fetcharg");
   return -1;
@@ -100,11 +99,11 @@ int
 argptr(int n, char **pp, int size)
 {
   uint64 i;
-  struct proc *curproc = myproc();
+  struct proc *p = myproc();
  
   if(argaddr(n, &i) < 0)
     return -1;
-  if(size < 0 || (uint)i >= curproc->sz || (uint)i+size > curproc->sz)
+  if(size < 0 || (uint)i >= p->sz || (uint)i+size > p->sz)
     return -1;
   *pp = (char*)i;
   return 0;
@@ -149,48 +148,47 @@ static int (*syscalls[])(void) = {
 [SYS_fork]    sys_fork,
 [SYS_exit]    sys_exit,
 [SYS_wait]    sys_wait,
-[SYS_pipe]    sys_pipe,
-[SYS_read]    sys_read,
-[SYS_kill]    sys_kill,
-[SYS_exec]    sys_exec,
-[SYS_fstat]   sys_fstat,
-[SYS_chdir]   sys_chdir,
-[SYS_dup]     sys_dup,
+//[SYS_pipe]    sys_pipe,
+//[SYS_read]    sys_read,
+//[SYS_kill]    sys_kill,
+//[SYS_exec]    sys_exec,
+//[SYS_fstat]   sys_fstat,
+//[SYS_chdir]   sys_chdir,
+//[SYS_dup]     sys_dup,
 [SYS_getpid]  sys_getpid,
-[SYS_sbrk]    sys_sbrk,
-[SYS_sleep]   sys_sleep,
-[SYS_uptime]  sys_uptime,
-[SYS_open]    sys_open,
-[SYS_write]   sys_write,
-[SYS_mknod]   sys_mknod,
-[SYS_unlink]  sys_unlink,
-[SYS_link]    sys_link,
-[SYS_mkdir]   sys_mkdir,
-[SYS_close]   sys_close,
+//[SYS_sbrk]    sys_sbrk,
+//[SYS_sleep]   sys_sleep,
+//[SYS_uptime]  sys_uptime,
+//[SYS_open]    sys_open,
+//[SYS_write]   sys_write,
+//[SYS_mknod]   sys_mknod,
+//[SYS_unlink]  sys_unlink,
+//[SYS_link]    sys_link,
+//[SYS_mkdir]   sys_mkdir,
+//[SYS_close]   sys_close,
 };
 
 static void
 dosyscall(void)
 {
   int num;
-  struct proc *curproc = myproc();
+  struct proc *p = myproc();
 
-  num = curproc->sf->rax;
+  num = p->tf->a7;
   if(num > 0 && num < NELEM(syscalls) && syscalls[num]) {
-    curproc->sf->rax = syscalls[num]();
+    p->tf->a0 = syscalls[num]();
   } else {
-    cprintf("%d %s: unknown sys call %d\n",
-            curproc->pid, curproc->name, num);
-    curproc->sf->rax = -1;
+    printf("%d %s: unknown sys call %d\n",
+            p->pid, p->name, num);
+    p->tf->a0 = -1;
   }
 }
 
 void
-syscall(struct sysframe *sf)
+syscall()
 {
     if(myproc()->killed)
       exit();
-    myproc()->sf = sf;
     dosyscall();
     if(myproc()->killed)
       exit();
diff --git a/sysfile.c b/sysfile.c
index d0de779..94f6437 100644
--- a/sysfile.c
+++ b/sysfile.c
@@ -41,11 +41,11 @@ static int
 fdalloc(struct file *f)
 {
   int fd;
-  struct proc *curproc = myproc();
+  struct proc *p = myproc();
 
   for(fd = 0; fd < NOFILE; fd++){
-    if(curproc->ofile[fd] == 0){
-      curproc->ofile[fd] = f;
+    if(p->ofile[fd] == 0){
+      p->ofile[fd] = f;
       return fd;
     }
   }
@@ -374,7 +374,7 @@ sys_chdir(void)
 {
   char *path;
   struct inode *ip;
-  struct proc *curproc = myproc();
+  struct proc *p = myproc();
   
   begin_op();
   if(argstr(0, &path) < 0 || (ip = namei(path)) == 0){
@@ -388,9 +388,9 @@ sys_chdir(void)
     return -1;
   }
   iunlock(ip);
-  iput(curproc->cwd);
+  iput(p->cwd);
   end_op();
-  curproc->cwd = ip;
+  p->cwd = ip;
   return 0;
 }
 
diff --git a/sysproc.c b/sysproc.c
index 0686d29..f840738 100644
--- a/sysproc.c
+++ b/sysproc.c
@@ -1,18 +1,11 @@
 #include "types.h"
-#include "x86.h"
+#include "riscv.h"
 #include "defs.h"
 #include "date.h"
 #include "param.h"
 #include "memlayout.h"
-#include "mmu.h"
 #include "proc.h"
 
-int
-sys_fork(void)
-{
-  return fork();
-}
-
 int
 sys_exit(void)
 {
@@ -20,12 +13,25 @@ sys_exit(void)
   return 0;  // not reached
 }
 
+int
+sys_getpid(void)
+{
+  return myproc()->pid;
+}
+
+int
+sys_fork(void)
+{
+  return fork();
+}
+
 int
 sys_wait(void)
 {
   return wait();
 }
 
+#if 0
 int
 sys_kill(void)
 {
@@ -36,12 +42,6 @@ sys_kill(void)
   return kill(pid);
 }
 
-int
-sys_getpid(void)
-{
-  return myproc()->pid;
-}
-
 int
 sys_sbrk(void)
 {
@@ -89,3 +89,4 @@ sys_uptime(void)
   release(&tickslock);
   return xticks;
 }
+#endif
diff --git a/trampoline.S b/trampoline.S
new file mode 100644
index 0000000..109dd93
--- /dev/null
+++ b/trampoline.S
@@ -0,0 +1,108 @@
+	#
+        # code to switch between user and kernel space.
+        #
+        # this code is mapped at the same virtual address
+        # in user and kernel space so that it can switch
+        # page tables.
+	#
+	# kernel.ld causes trampstart to be aligned
+        # to a page boundary.
+        #
+.globl usertrap
+	.section trampoline
+.globl trampstart
+trampstart:
+        # switch from kernel to user.
+	# a0: p->tf in user page table
+        # a1: new value for satp, for user page table
+
+        # switch to user page table
+        csrw satp, a1
+
+        # put the saved user a0 in sscratch, so we
+        # can swap it with our a0 (p->tf) in the last step.
+        ld t0, 80(a0)
+        csrw sscratch, t0
+
+        # restore all but a0 from p->tf
+        ld ra, 32(a0)
+        ld sp, 40(a0)
+        ld gp, 48(a0)
+        ld tp, 56(a0)
+        ld t0, 64(a0)
+        ld t1, 72(a0)
+        ld t2, 80(a0)
+        ld a1, 96(a0)
+        ld a2, 104(a0)
+        ld a3, 112(a0)
+        ld a4, 120(a0)
+        ld a5, 128(a0)
+        ld a6, 136(a0)
+        ld a7, 144(a0)
+        ld t3, 152(a0)
+        ld t4, 160(a0)
+        ld t5, 168(a0)
+        ld t6, 176(a0)
+
+	# restore user a0, and save p->tf
+        csrrw a0, sscratch, a0
+        
+        # return to user mode and user pc.
+        # caller has set up sstatus and sepc.
+        sret
+
+	#
+        # trap.c set stvec to point here, so
+        # interrupts and exceptions start here,
+        # in supervisor mode, but with a
+        # user page table.
+        #
+        # sscratch points to where the process's p->tf is
+        # mapped into user space (TRAMPOLINE - 4096).
+        #
+.align 4
+.globl trampvec
+trampvec:    
+	# swap a0 and sscratch
+        # so that a0 is p->tf
+        csrrw a0, sscratch, a0
+
+        # save the user registers in p->tf
+        sd ra, 32(a0)
+        sd sp, 40(a0)
+        sd gp, 48(a0)
+        sd tp, 56(a0)
+        sd t0, 64(a0)
+        sd t1, 72(a0)
+        sd t2, 80(a0)
+        sd a1, 96(a0)
+        sd a2, 104(a0)
+        sd a3, 112(a0)
+        sd a4, 120(a0)
+        sd a5, 128(a0)
+        sd a6, 136(a0)
+        sd a7, 144(a0)
+        sd t3, 152(a0)
+        sd t4, 160(a0)
+        sd t5, 168(a0)
+        sd t6, 176(a0)
+
+	# save the user a0 in p->tf->a0
+        csrr t0, sscratch
+        sd t0, 80(a0)
+
+        # restore kernel stack pointer from p->tf->kernel_sp
+        ld sp, 8(a0)
+
+        # remember the address of usertrap(), p->tf->kernel_trap
+        ld t0, 16(a0)
+
+        # restore kernel page table from p->tf->kernel_satp
+        ld t1, 0(a0)
+        csrw satp, t1
+
+        # a0 is no longer valid, since the kernel page
+        # table does not specially map p->td.
+
+        # jump to usertrap(), which does not return
+        jr t0
diff --git a/trap.c b/trap.c
index 4c58cb2..d0368ce 100644
--- a/trap.c
+++ b/trap.c
@@ -1,109 +1,113 @@
 #include "types.h"
-#include "defs.h"
 #include "param.h"
 #include "memlayout.h"
-#include "mmu.h"
+#include "riscv.h"
 #include "proc.h"
-#include "x86.h"
-#include "traps.h"
 #include "spinlock.h"
+#include "defs.h"
 
-// Interrupt descriptor table (shared by all CPUs).
-struct intgate idt[256];
-extern uint64 vectors[];  // in vectors.S: array of 256 entry pointers
 struct spinlock tickslock;
 uint ticks;
 
+extern char trampstart[], trampvec[];
+
+void kerneltrap();
+
 void
-tvinit(void)
+trapinit(void)
 {
   int i;
 
-  for(i=0; i<256; i++) {
-    idt[i] = INTDESC(SEG_KCODE, vectors[i], INT_P | SEG_INTR64);
-  }
-  idtinit();
-    
+  // send interrupts and exceptions to kerneltrap().
+  w_stvec((uint64)kerneltrap);
+
   initlock(&tickslock, "time");
 }
 
+//
+// handle an interrupt, exception, or system call from user space.
+// called from trampoline.S
+//
 void
-idtinit(void)
+usertrap(void)
 {
-  struct desctr dtr;
+  if((r_sstatus() & SSTATUS_SPP) != 0)
+    panic("usertrap: not from user mode");
 
-  dtr.limit = sizeof(idt) - 1;
-  dtr.base = (uint64)idt;
-  lidt((void *)&dtr.limit);
-}
+  // send interrupts and exceptions to kerneltrap(),
+  // since we're now in the kernel.
+  w_stvec((uint64)kerneltrap);
 
-//PAGEBREAK: 41
-void
-trap(struct trapframe *tf)
-{
-  switch(tf->trapno){
-  case T_IRQ0 + IRQ_TIMER:
-    if(cpuid() == 0){
-      acquire(&tickslock);
-      ticks++;
-      wakeup(&ticks);
-      release(&tickslock);
-    }
-    lapiceoi();
-    break;
-  case T_IRQ0 + IRQ_IDE:
-    ideintr();
-    lapiceoi();
-    break;
-  case T_IRQ0 + IRQ_IDE+1:
-    // Bochs generates spurious IDE1 interrupts.
-    break;
-  case T_IRQ0 + IRQ_KBD:
-    kbdintr();
-    lapiceoi();
-    break;
-  case T_IRQ0 + IRQ_COM1:
-    uartintr();
-    lapiceoi();
-    break;
-  case T_IRQ0 + 7:
-  case T_IRQ0 + IRQ_SPURIOUS:
-    cprintf("cpu%d: spurious interrupt at %x:%x\n",
-            cpuid(), tf->cs, tf->rip);
-    lapiceoi();
-    break;
+  struct proc *p = myproc();
+  
+  // save user program counter.
+  p->tf->epc = r_sepc();
+  
+  if(r_scause() == 8){
+    // system call
+    printf("usertrap(): system call pid=%d syscall=%d\n", p->pid, p->tf->a7);
 
-  //PAGEBREAK: 13
-  default:
-    if(myproc() == 0 || (tf->cs&3) == 0){
-      // In kernel, it must be our mistake.
-      cprintf("unexpected trap %d from cpu %d rip %x (cr2=0x%x)\n",
-              tf->trapno, cpuid(), tf->rip, rcr2());
-      panic("trap");
-    }
-    // In user space, assume process misbehaved.
-    cprintf("pid %d %s: trap %d err %d on cpu %d "
-            "rip 0x%x addr 0x%x--kill proc\n",
-            myproc()->pid, myproc()->name, tf->trapno,
-            tf->err, cpuid(), tf->rip, rcr2());
-    myproc()->killed = 1;
+    // sepc points to the ecall instruction,
+    // but we want to return to the next instruction.
+    p->tf->epc += 4;
+
+    syscall();
+  } else {
+    printf("usertrap(): unexpected scause 0x%x pid=%d\n", r_scause(), p->pid);
+    panic("usertrap");
   }
 
-  // Force process exit if it has been killed and is in user space.
-  // (If it is still executing in the kernel, let it keep running
-  // until it gets to the regular system call return.)
-  if(myproc() && myproc()->killed && (tf->cs&3) == DPL_USER)
-    exit();
-
-  // Force process to give up CPU on clock tick.
-  // If interrupts were on while locks held, would need to check nlock.
-  if(myproc() && myproc()->state == RUNNING &&
-     tf->trapno == T_IRQ0+IRQ_TIMER)
-    yield();
-  
-  // Check if the process has been killed since we yielded
-  if(myproc() && myproc()->killed && (tf->cs&3) == DPL_USER)
-    exit();
+  usertrapret();
 }
 
+//
+// return to user space
+//
+void
+usertrapret(void)
+{
+  struct proc *p = myproc();
 
+  // XXX turn off interrupts, since we're switching
+  // now from kerneltrap() to usertrap().
+
+  // send interrupts and exceptions to trampoline.S
+  w_stvec(TRAMPOLINE + (trampvec - trampstart));
+
+  // set up values that trampoline.S will need when
+  // the process next re-enters the kernel.
+  p->tf->kernel_satp = r_satp();
+  p->tf->kernel_sp = (uint64)p->kstack + PGSIZE;
+  p->tf->kernel_trap = (uint64)usertrap;
+
+  // set up the registers that trampoline.S's sret will use
+  // to get to user space.
+  
+  // set S Previous Privilege mode to User.
+  unsigned long x = r_sstatus();
+  x &= ~SSTATUS_SPP; // clear SPP to 0 for user mode
+  w_sstatus(x);
+
+  // set S Exception Program Counter to the saved user pc.
+  w_sepc(p->tf->epc);
+
+  // tell trampline.S the user page table to switch to.
+  uint64 satp = MAKE_SATP(p->pagetable);
+
+  // jump to trampoline.S at the top of memory, which 
+  // switches to the user page table, restores user registers,
+  // and switches to user mode with sret.
+  ((void (*)(uint64,uint64))TRAMPOLINE)(TRAMPOLINE - PGSIZE, satp);
+}
+
+// interrupts and exceptions from kernel code go here,
+// on whatever the current kernel stack is.
+// must be 4-byte aligned to fit in stvec.
+void __attribute__ ((aligned (4)))
+kerneltrap()
+{
+  if((r_sstatus() & SSTATUS_SPP) == 0)
+    panic("kerneltrap: not from supervisor mode");
+
+  panic("kerneltrap");
+}
diff --git a/traps.h b/traps.h
deleted file mode 100644
index 6e8a444..0000000
--- a/traps.h
+++ /dev/null
@@ -1,36 +0,0 @@
-// x86 trap and interrupt constants.
-
-// Processor-defined:
-#define T_DIVIDE         0      // divide error
-#define T_DEBUG          1      // debug exception
-#define T_NMI            2      // non-maskable interrupt
-#define T_BRKPT          3      // breakpoint
-#define T_OFLOW          4      // overflow
-#define T_BOUND          5      // bounds check
-#define T_ILLOP          6      // illegal opcode
-#define T_DEVICE         7      // device not available
-#define T_DBLFLT         8      // double fault
-// #define T_COPROC      9      // reserved (not used since 486)
-#define T_TSS           10      // invalid task switch segment
-#define T_SEGNP         11      // segment not present
-#define T_STACK         12      // stack exception
-#define T_GPFLT         13      // general protection fault
-#define T_PGFLT         14      // page fault
-// #define T_RES        15      // reserved
-#define T_FPERR         16      // floating point error
-#define T_ALIGN         17      // aligment check
-#define T_MCHK          18      // machine check
-#define T_SIMDERR       19      // SIMD floating point error
-
-#define T_DEFAULT      500      // catchall
-
-#define T_IRQ0          32      // IRQ 0 corresponds to int T_IRQ
-
-#define IRQ_TIMER        0
-#define IRQ_KBD          1
-#define IRQ_COM1         4
-#define IRQ_IDE         14
-#define IRQ_ERROR       19
-#define IRQ_SPURIOUS    31
-
-
diff --git a/uart.c b/uart.c
index b8946da..9a77c5a 100644
--- a/uart.c
+++ b/uart.c
@@ -1,77 +1,51 @@
-// Intel 8250 serial port (UART).
+#include "memlayout.h"
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "traps.h"
-#include "spinlock.h"
-#include "sleeplock.h"
-#include "fs.h"
-#include "file.h"
-#include "mmu.h"
-#include "proc.h"
-#include "x86.h"
+//
+// qemu -machine virt has a 16550a UART
+// qemu/hw/riscv/virt.c
+// http://byterunner.com/16550.html
+//
+// caller should lock.
+//
 
-#define COM1    0x3f8
-
-static int uart;    // is there a uart?
+// address of one of the registers
+#define R(reg) ((unsigned int*)(UART0 + 4*(reg)))
 
 void
 uartinit(void)
 {
-  char *p;
+  // disable interrupts
+  *R(1) = 0x00;
 
-  // Turn off the FIFO
-  outb(COM1+2, 0);
+  // special mode to set baud rate
+  *R(3) = 0x80;
 
-  // 9600 baud, 8 data bits, 1 stop bit, parity off.
-  outb(COM1+3, 0x80);    // Unlock divisor
-  outb(COM1+0, 115200/9600);
-  outb(COM1+1, 0);
-  outb(COM1+3, 0x03);    // Lock divisor, 8 data bits.
-  outb(COM1+4, 0);
-  outb(COM1+1, 0x01);    // Enable receive interrupts.
+  // LSB for baud rate of 38.4K
+  *R(0) = 0x03;
 
-  // If status is 0xFF, no serial port.
-  if(inb(COM1+5) == 0xFF)
-    return;
-  uart = 1;
+  // MSB for baud rate of 38.4K
+  *R(1) = 0x00;
 
-  // Acknowledge pre-existing interrupt conditions;
-  // enable interrupts.
-  inb(COM1+2);
-  inb(COM1+0);
-  ioapicenable(IRQ_COM1, 0);
+  // leave set-baud mode,
+  // and set word length to 8 bits, no parity.
+  *R(3) = 0x03;
 
-  // Announce that we're here.
-  for(p="xv6...\n"; *p; p++)
-    uartputc(*p);
+  // reset and enable FIFOs.
+  *R(2) = 0x07;
 }
 
 void
 uartputc(int c)
 {
-  int i;
-
-  if(!uart)
-    return;
-  for(i = 0; i < 128 && !(inb(COM1+5) & 0x20); i++)
-    microdelay(10);
-  outb(COM1+0, c);
+  *R(0) = c;
 }
 
 static int
 uartgetc(void)
 {
-  if(!uart)
-    return -1;
-  if(!(inb(COM1+5) & 0x01))
-    return -1;
-  return inb(COM1+0);
 }
 
 void
 uartintr(void)
 {
-  consoleintr(uartgetc);
 }
diff --git a/vm.c b/vm.c
index c0276a1..8c2ccb3 100644
--- a/vm.c
+++ b/vm.c
@@ -1,230 +1,162 @@
 #include "param.h"
 #include "types.h"
-#include "defs.h"
-#include "x86.h"
-#include "msr.h"
 #include "memlayout.h"
-#include "mmu.h"
-#include "proc.h"
 #include "elf.h"
-#include "traps.h"
+#include "riscv.h"
+#include "defs.h"
 
-extern char data[];  // defined by kernel.ld
-void sysentry(void);
+/*
+ * the kernel's page table.
+ */
+pagetable_t kernel_pagetable;
 
-static pde_t *kpml4; // kernel address space, used by scheduler and bootup
+extern char etext[];  // kernel.ld sets this to end of kernel code.
 
-// Bootstrap GDT.  Used by boot.S but defined in C
-// Map "logical" addresses to virtual addresses using identity map.
-// Cannot share a CODE descriptor for both kernel and user
-// because it would have to have DPL_USR, but the CPU forbids
-// an interrupt from CPL=0 to DPL=3.
-struct segdesc bootgdt[NSEGS] = {
-  [0] = SEGDESC(0, 0, 0),  // null
-  [1] = SEGDESC(0, 0xfffff, SEG_R|SEG_CODE|SEG_S|SEG_DPL(0)|SEG_P|SEG_D|SEG_G),  // 32-bit kernel code
-  [2] = SEGDESC(0, 0, SEG_R|SEG_CODE|SEG_S|SEG_DPL(0)|SEG_P|SEG_L|SEG_G),  // 64-bit kernel code
-  [3] = SEGDESC(0, 0xfffff, SEG_W|SEG_S|SEG_DPL(0)|SEG_P|SEG_D|SEG_G),       // kernel data
-  // The order of the user data and user code segments is
-  // important for syscall instructions.  See initseg.
-  [6] = SEGDESC(0, 0xfffff, SEG_W|SEG_S|SEG_DPL(3)|SEG_P|SEG_D|SEG_G),   // 64-bit user data
-  [7] = SEGDESC(0, 0, SEG_R|SEG_CODE|SEG_S|SEG_DPL(3)|SEG_P|SEG_L|SEG_G),    // 64-bit user code
-};
+extern char trampstart[]; // trampoline.S
 
-
-// Set up CPU's kernel segment descriptors.
-// Run once on entry on each CPU.
+/*
+ * create a direct-map page table for the kernel and
+ * turn on paging. called early, in supervisor mode.
+ * the page allocator is already initialized.
+ */
 void
-seginit(void)
+kvminit()
 {
-  struct cpu *c;
-  struct desctr dtr;
+  kernel_pagetable = (pagetable_t) kalloc();
+  memset(kernel_pagetable, 0, PGSIZE);
 
-  c = getmycpu();
+  // uart registers
+  mappages(kernel_pagetable, UART0, PGSIZE,
+           UART0, PTE_R | PTE_W);
+
+  // map kernel text executable and read-only.
+  mappages(kernel_pagetable, KERNBASE, (uint64)etext-KERNBASE,
+           KERNBASE, PTE_R | PTE_X);
   
-  memmove(c->gdt, bootgdt, sizeof bootgdt);
-  dtr.limit = sizeof(c->gdt)-1;
-  dtr.base = (uint64) c->gdt;
-  lgdt((void *)&dtr.limit);
+  // map kernel data and the physical RAM we'll make use of.
+  mappages(kernel_pagetable, (uint64)etext, PHYSTOP-(uint64)etext,
+           (uint64)etext, PTE_R | PTE_W);
 
-  // When executing a syscall instruction the CPU sets the SS selector
-  // to (star >> 32) + 8 and the CS selector to (star >> 32).
-  // When executing a sysret instruction the CPU sets the SS selector
-  // to (star >> 48) + 8 and the CS selector to (star >> 48) + 16.
-  uint64 star = ((((uint64)SEG_UCODE|0x3)- 16)<<48)|((uint64)(SEG_KCODE)<<32);
-  writemsr(MSR_STAR, star);
-  writemsr(MSR_LSTAR, (uint64)&sysentry);
-  writemsr(MSR_SFMASK, FL_TF | FL_IF);
+  // map the trampoline for trap entry/exit to
+  // the highest virtual address in the kernel.
+  mappages(kernel_pagetable, TRAMPOLINE, PGSIZE,
+           (uint64)trampstart, PTE_R | PTE_X);
 
-  // Initialize cpu-local storage so that each core can easily
-  // find its struct cpu using %gs.
-  writegs(SEG_KDATA);
-  writemsr(MSR_GS_BASE, (uint64)c);
-  writemsr(MSR_GS_KERNBASE, (uint64)c);
-  c->cpu = c;
+  kvmswitch();
 }
 
-// Return the address of the PTE in page table pgdir
+// Switch h/w page table register to the kernel's page table,
+// and enable paging.
+void
+kvmswitch(void)
+{
+  w_satp(MAKE_SATP(kernel_pagetable));
+}
+
+// Return the address of the PTE in page table pagetable
 // that corresponds to virtual address va.  If alloc!=0,
 // create any required page table pages.
+//
+// The risc-v Sv39 scheme has three levels of page table
+// pages. A page table page contains 512 64-bit PTEs.
+// A 64-bit virtual address is split into five fields:
+//   39..63 -- must be zero.
+//   30..38 -- 9 bits of level-2 index.
+//   21..39 -- 9 bits of level-1 index.
+//   12..20 -- 9 bits of level-0 index.
+//    0..12 -- 12 bits of byte offset within the page.
 static pte_t *
-walkpgdir(pde_t *pml4, const void *va, int alloc)
+walk(pagetable_t pagetable, const void *va, int alloc)
 {
-  pde_t *pgdir = pml4;
-  pde_t *pde;
-  int level;
-  
-  for (level = L_PML4; level > 0; level--) {
-    pde = &pgdir[PX(level, va)];
-    if(*pde & PTE_P)
-      pgdir = (pte_t*)P2V(PTE_ADDR(*pde));
-    else {
-      if(!alloc || (pgdir = (pde_t*)kalloc()) == 0)
+  if((uint64)va >= MAXVA)
+    panic("walk");
+
+  for(int level = 2; level > 0; level--) {
+    pte_t *pte = &pagetable[PX(level, va)];
+    if(*pte & PTE_V) {
+      pagetable = (pagetable_t)PTE2PA(*pte);
+    } else {
+      if(!alloc || (pagetable = (pde_t*)kalloc()) == 0)
         return 0;
-      memset(pgdir, 0, PGSIZE);
-      *pde = V2P(pgdir) | PTE_P | PTE_W | PTE_U;
+      memset(pagetable, 0, PGSIZE);
+      *pte = PA2PTE(pagetable) | PTE_V;
     }
   }
-  return &pgdir[PX(level, va)];
+  return &pagetable[PX(0, 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, uint64 size, uint64 pa, int perm)
+void
+mappages(pagetable_t pagetable, uint64 va, uint64 size, uint64 pa, int perm)
 {
   char *a, *last;
   pte_t *pte;
 
-  a = (char*)PGROUNDDOWN((uint64)va);
-  last = (char*)PGROUNDDOWN(((uint64)va) + size - 1);
+  a = (char*)PGROUNDDOWN(va);
+  last = (char*)PGROUNDDOWN(va + size - 1);
   for(;;){
-    if((pte = walkpgdir(pgdir, a, 1)) == 0)
-      return -1;
-    if(*pte & PTE_P)
+    if((pte = walk(pagetable, a, 1)) == 0)
+      panic("mappages: walk");
+    if(*pte & PTE_V)
       panic("remap");
-    *pte = pa | perm | PTE_P;
+    *pte = PA2PTE(pa) | perm | PTE_V;
     if(a == last)
       break;
     a += PGSIZE;
     pa += PGSIZE;
   }
-  return 0;
 }
 
-// There is one page table per process, plus one that's used when
-// a CPU is not running any process (kpml4). The kernel uses the
-// current process's page table during system calls and interrupts;
-// page protection bits prevent user code from using the kernel's
-// mappings.
-//
-// setupkvm() and exec() set up every page table like this:
-//
-//   0..KERNBASE: user memory (text+data+stack+heap), mapped to
-//                phys memory allocated by the kernel
-//   KERNBASE..KERNBASE+EXTMEM: mapped to 0..EXTMEM (for I/O space)
-//   KERNBASE+EXTMEM..data: mapped to EXTMEM..V2P(data)
-//                for the kernel's instructions and r/o data
-//   data..KERNBASE+PHYSTOP: mapped to V2P(data)..PHYSTOP,
-//                                  rw data + free physical memory
-//   0xfe000000..0: mapped direct (devices such as ioapic)
-//
-// The kernel allocates physical memory for its heap and for user memory
-// between V2P(end) and the end of physical memory (PHYSTOP)
-// (directly addressable from end..P2V(PHYSTOP)).
-
-// This table defines the kernel's mappings, which are present in
-// every process's page table.
-static struct kmap {
-  void *virt;
-  uint64 phys_start;
-  uint64 phys_end;
-  int perm;
-} kmap[] = {
- { (void*)KERNBASE, 0,             EXTMEM,    PTE_W}, // I/O space
- { (void*)KERNLINK, V2P(KERNLINK), V2P(data), 0},     // kern text+rodata
- { (void*)data,     V2P(data),     PHYSTOP,   PTE_W}, // kern data+memory
- { (void*)P2V(DEVSPACE), DEVSPACE, DEVSPACETOP, PTE_W}, // more devices
-};
-
-// Set up kernel part of a page table.
-pde_t*
-setupkvm(void)
+// Remove mappings from a page table. The mappings in
+// the given range must exist. Optionally free the
+// physical memory.
+void
+unmappages(pagetable_t pagetable, uint64 va, uint64 size, int do_free)
 {
-  pde_t *pml4;
-  struct kmap *k;
+  char *a, *last;
+  pte_t *pte;
+  uint64 pa;
 
-  if((pml4 = (pde_t*)kalloc()) == 0)
-    return 0;
-  memset(pml4, 0, PGSIZE);
-  if (PHYSTOP > DEVSPACE)
-    panic("PHYSTOP too high");
-  for(k = kmap; k < &kmap[NELEM(kmap)]; k++) {
-    if(mappages(pml4, k->virt, k->phys_end - k->phys_start,
-                (uint)k->phys_start, k->perm) < 0) {
-      freevm(pml4, 0);
-      return 0;
+  a = (char*)PGROUNDDOWN(va);
+  last = (char*)PGROUNDDOWN(va + size - 1);
+  for(;;){
+    if((pte = walk(pagetable, a, 0)) == 0)
+      panic("unmappages: walk");
+    if((*pte & PTE_V) == 0)
+      panic("unmappages: not mapped");
+    if(PTE_FLAGS(*pte) == PTE_V)
+      panic("unmappages: not a leaf");
+    if(do_free){
+      pa = PTE2PA(*pte);
+      kfree((void*)pa);
     }
+    *pte = 0;
+    if(a == last)
+      break;
+    a += PGSIZE;
+    pa += PGSIZE;
   }
-  return pml4;
 }
 
-// Allocate one page table for the machine for the kernel address
-// space for scheduler processes.
-void
-kvmalloc(void)
+// create an empty user page table.
+pagetable_t
+uvmcreate()
 {
-  kpml4 = setupkvm();
-  switchkvm();
+  pagetable_t pagetable;
+  pagetable = (pagetable_t) kalloc();
+  if(pagetable == 0)
+    panic("uvmcreate: out of memory");
+  memset(pagetable, 0, PGSIZE);
+  return pagetable;
 }
 
-// Switch h/w page table register to the kernel-only page table,
-// for when no process is running.
-void
-switchkvm(void)
-{
-  lcr3(V2P(kpml4));   // switch to the kernel page table
-}
-
-
-// Switch TSS and h/w page table to correspond to process p.
-void
-switchuvm(struct proc *p)
-{
-  struct desctr dtr;
-  struct cpu *c;
-  
-  if(p == 0)
-    panic("switchuvm: no process");
-  if(p->kstack == 0)
-    panic("switchuvm: no kstack");
-  if(p->pgdir == 0)
-    panic("switchuvm: no pgdir");
-
-  pushcli();
-
-  c = mycpu();
-  uint64 base = (uint64) &(c->ts);
-  c->gdt[SEG_TSS>>3] =  SEGDESC(base, (sizeof(c->ts)-1), SEG_P|SEG_TSS64A);
-  c->gdt[(SEG_TSS>>3)+1] = SEGDESCHI(base);
-  c->ts.rsp[0] = (uint64) p->kstack + KSTACKSIZE;
-  c->ts.iomba = (ushort) 0xFFFF;
-
-  dtr.limit = sizeof(c->gdt) - 1;
-  dtr.base = (uint64)c->gdt;
-  lgdt((void *)&dtr.limit);
-
-  ltr(SEG_TSS);
-
-  lcr3(V2P(p->pgdir));  // switch to process's address space
-
-  popcli();
-}
-
-// Load the initcode into address 0 of pgdir.
+// Load the user initcode into address 0 of pagetable,
+// for the very first process.
 // sz must be less than a page.
 void
-inituvm(pde_t *pgdir, char *init, uint sz)
+uvminit(pagetable_t pagetable, char *src, uint sz)
 {
   char *mem;
 
@@ -232,63 +164,8 @@ inituvm(pde_t *pgdir, char *init, uint sz)
     panic("inituvm: more than a page");
   mem = kalloc();
   memset(mem, 0, PGSIZE);
-  mappages(pgdir, 0, PGSIZE, V2P(mem), PTE_W|PTE_U);
-  memmove(mem, init, sz);
-}
-
-// Load a program segment into pgdir.  addr must be page-aligned
-// and the pages from addr to addr+sz must already be mapped.
-int
-loaduvm(pde_t *pgdir, char *addr, struct inode *ip, uint offset, uint sz)
-{
-  uint i, n;
-  uint64 pa;
-  pte_t *pte;
-
-  if((uint64) addr % PGSIZE != 0)
-    panic("loaduvm: addr must be page aligned");
-  for(i = 0; i < sz; i += PGSIZE){
-    if((pte = walkpgdir(pgdir, addr+i, 0)) == 0)
-      panic("loaduvm: address should exist");
-    pa = PTE_ADDR(*pte);
-    if(sz - i < PGSIZE)
-      n = sz - i;
-    else
-      n = PGSIZE;
-    if(readi(ip, P2V(pa), offset+i, n) != n)
-      return -1;
-  }
-  return 0;
-}
-
-// Allocate page tables and physical memory to grow process from oldsz to
-// newsz, which need not be page aligned.  Returns new size or 0 on error.
-int
-allocuvm(pde_t *pgdir, uint oldsz, uint newsz)
-{
-  char *mem;
-  uint64 a;
-
-  if(newsz >= KERNBASE)
-    return 0;
-  if(newsz < oldsz)
-    return oldsz;
-
-  a = PGROUNDUP(oldsz);
-  for(; a < newsz; a += PGSIZE){
-    mem = kalloc();
-    if(mem == 0){
-      deallocuvm(pgdir, newsz, oldsz);
-      return 0;
-    }
-    memset(mem, 0, PGSIZE);
-    if(mappages(pgdir, (char*)a, PGSIZE, V2P(mem), PTE_W|PTE_U) < 0){
-      deallocuvm(pgdir, newsz, oldsz);
-      kfree(mem);
-      return 0;
-    }
-  }
-  return newsz;
+  mappages(pagetable, 0, PGSIZE, (uint64)mem, PTE_W|PTE_R|PTE_X|PTE_U);
+  memmove(mem, src, sz);
 }
 
 // Deallocate user pages to bring the process size from oldsz to
@@ -296,153 +173,66 @@ allocuvm(pde_t *pgdir, uint oldsz, uint newsz)
 // need to be less than oldsz.  oldsz can be larger than the actual
 // process size.  Returns the new process size.
 int
-deallocuvm(pde_t *pml4, uint64 oldsz, uint64 newsz)
+uvmdealloc(pagetable_t pagetable, uint64 oldsz, uint64 newsz)
 {
-  pte_t *pte;
-  uint64 a, pa;
-
   if(newsz >= oldsz)
     return oldsz;
-
-  a = PGROUNDUP(newsz);
-  for(; a  < oldsz; a += PGSIZE){
-    pte = walkpgdir(pml4, (char*)a, 0);
-    if(!pte)
-      continue;
-    else if((*pte & PTE_P) != 0){
-      pa = PTE_ADDR(*pte);
-      if(pa == 0)
-        panic("kfree");
-      char *v = P2V(pa);
-      kfree(v);
-      *pte = 0;
-    }
-  }
+  unmappages(pagetable, newsz, oldsz - newsz, 1);
   return newsz;
 }
 
-// Recursively free a page table
-void
-freelevel(pde_t *pgtab, int level) {
-  int i;
-  pde_t *pd;
-  
-  if (level > 0) {
-    for(i = 0; i < NPDENTRIES; i++) {
-      if(pgtab[i] & PTE_P){
-        pd = (pde_t*)P2V(PTE_ADDR(pgtab[i]));
-        freelevel(pd, level-1);
-      }
+// Recursively free page table pages.
+// All leaf mappings must already have been removed.
+static void
+freewalk(pagetable_t pagetable)
+{
+  // there are 2^9 = 512 PTEs in a page table.
+  for(int i = 0; i < 512; i++){
+    pte_t pte = pagetable[i];
+    if((pte & PTE_V) && (pte & (PTE_R|PTE_W|PTE_X)) == 0){
+      // this PTE points to a lower-level page table.
+      uint64 child = PTE2PA(pte);
+      freewalk((pagetable_t)child);
+      pagetable[i] = 0;
+    } else if(pte & PTE_V){
+      // XXX trampoline pages...
+      panic("freewalk: leaf");
     }
   }
-  kfree((char*)pgtab);
+  kfree((void*)pagetable);
 }
 
-// Free all the physical memory pages
-// in the user part and page table
+// Free user memory pages,
+// then free page table pages.
 void
-freevm(pde_t *pml4, uint64 sz)
+uvmfree(pagetable_t pagetable, uint64 sz)
 {
-  if(pml4 == 0)
-    panic("freevm: no pgdir");
-
-  deallocuvm(pml4, sz, 0);
-  freelevel(pml4, L_PML4);
+  unmappages(pagetable, 0, sz, 1);
+  freewalk(pagetable);
 }
 
-// Clear PTE_U on a page. Used to create an inaccessible
-// page beneath the user stack.
+// Given a parent process's page table, copy
+// its memory into a child's page table.
+// Copies both the page table and the
+// physical memory.
 void
-clearpteu(pde_t *pgdir, char *uva)
+uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
 {
   pte_t *pte;
-
-  pte = walkpgdir(pgdir, uva, 0);
-  if(pte == 0)
-    panic("clearpteu");
-  *pte &= ~PTE_U;
-}
-
-// Given a parent process's page table, create a copy
-// of it for a child.
-pde_t*
-copyuvm(pde_t *pgdir, uint sz)
-{
-  pde_t *d;
-  pte_t *pte;
   uint64 pa, i;
   uint flags;
   char *mem;
 
-  if((d = setupkvm()) == 0)
-    return 0;
   for(i = 0; i < sz; i += PGSIZE){
-    if((pte = walkpgdir(pgdir, (void *) i, 0)) == 0)
+    if((pte = walk(old, (void *) i, 0)) == 0)
       panic("copyuvm: pte should exist");
-    if(!(*pte & PTE_P))
+    if((*pte & PTE_V) == 0)
       panic("copyuvm: page not present");
-    pa = PTE_ADDR(*pte);
+    pa = PTE2PA(*pte);
     flags = PTE_FLAGS(*pte);
     if((mem = kalloc()) == 0)
-      goto bad;
-    memmove(mem, (char*)P2V(pa), PGSIZE);
-    if(mappages(d, (void*)i, PGSIZE, V2P(mem), flags) < 0) {
-      kfree(mem);
-      goto bad;
-    }
+      panic("uvmcopy: kalloc failed");
+    memmove(mem, (char*)pa, PGSIZE);
+    mappages(new, i, PGSIZE, (uint64)mem, flags);
   }
-  return d;
-
-bad:
-  freevm(d, sz);
-  return 0;
 }
-
-//PAGEBREAK!
-// Map user virtual address to kernel address.
-char*
-uva2ka(pde_t *pgdir, char *uva)
-{
-  pte_t *pte;
-
-  pte = walkpgdir(pgdir, uva, 0);
-  if((*pte & PTE_P) == 0)
-    return 0;
-  if((*pte & PTE_U) == 0)
-    return 0;
-  return (char*)P2V(PTE_ADDR(*pte));
-}
-
-// Copy len bytes from p to user address va in page table pgdir.
-// Most useful when pgdir is not the current page table.
-// uva2ka ensures this only works for PTE_U pages.
-int
-copyout(pde_t *pgdir, uint va, void *p, uint len)
-{
-  char *buf, *pa0;
-  uint64 n, va0;
-
-  buf = (char*)p;
-  while(len > 0){
-    va0 = (uint)PGROUNDDOWN(va);
-    pa0 = uva2ka(pgdir, (char*)va0);
-    if(pa0 == 0)
-      return -1;
-    n = PGSIZE - (va - va0);
-    if(n > len)
-      n = len;
-    memmove(pa0 + (va - va0), buf, n);
-    len -= n;
-    buf += n;
-    va = va0 + PGSIZE;
-  }
-  return 0;
-}
-
-//PAGEBREAK!
-// Blank page.
-//PAGEBREAK!
-// Blank page.
-//PAGEBREAK!
-// Blank page.
-
diff --git a/x86.h b/x86.h
deleted file mode 100644
index 1ae64ac..0000000
--- a/x86.h
+++ /dev/null
@@ -1,198 +0,0 @@
-// Routines to let C code use special x86 instructions.
-
-#ifndef __ASSEMBLER__
-
-static inline uchar
-inb(ushort port)
-{
-  uchar data;
-
-  asm volatile("in %1,%0" : "=a" (data) : "d" (port));
-  return data;
-}
-
-static inline void
-insl(int port, void *addr, int cnt)
-{
-  asm volatile("cld; rep insl" :
-               "=D" (addr), "=c" (cnt) :
-               "d" (port), "0" (addr), "1" (cnt) :
-               "memory", "cc");
-}
-
-static inline void
-outb(ushort port, uchar data)
-{
-  asm volatile("out %0,%1" : : "a" (data), "d" (port));
-}
-
-static inline void
-outw(ushort port, ushort data)
-{
-  asm volatile("out %0,%1" : : "a" (data), "d" (port));
-}
-
-static inline void
-outsl(int port, const void *addr, int cnt)
-{
-  asm volatile("cld; rep outsl" :
-               "=S" (addr), "=c" (cnt) :
-               "d" (port), "0" (addr), "1" (cnt) :
-               "cc");
-}
-
-static inline void
-stosb(void *addr, int data, int cnt)
-{
-  asm volatile("cld; rep stosb" :
-               "=D" (addr), "=c" (cnt) :
-               "0" (addr), "1" (cnt), "a" (data) :
-               "memory", "cc");
-}
-
-static inline void
-stosl(void *addr, int data, int cnt)
-{
-  asm volatile("cld; rep stosl" :
-               "=D" (addr), "=c" (cnt) :
-               "0" (addr), "1" (cnt), "a" (data) :
-               "memory", "cc");
-}
-
-static inline void
-lgdt(void *p)
-{
-  asm volatile("lgdt (%0)" : : "r" (p) : "memory");
-}
-
-static inline void
-lidt(void *p)
-{
-  asm volatile("lidt (%0)" : : "r" (p) : "memory");
-}
-
-static inline void
-ltr(ushort sel)
-{
-  asm volatile("ltr %0" : : "r" (sel));
-}
-
-static inline uint64
-readeflags(void)
-{
-  uint64 eflags;
-  asm volatile("pushf; pop %0" : "=r" (eflags));
-  return eflags;
-}
-
-static inline void
-loadgs(ushort v)
-{
-  asm volatile("movw %0, %%gs" : : "r" (v));
-}
-
-static inline void
-cli(void)
-{
-  asm volatile("cli");
-}
-
-static inline void
-sti(void)
-{
-  asm volatile("sti");
-}
-
-static inline uint
-xchg(volatile uint *addr, uint newval)
-{
-  uint result;
-
-  // The + in "+m" denotes a read-modify-write operand.
-  asm volatile("lock; xchgl %0, %1" :
-               "+m" (*addr), "=a" (result) :
-               "1" (newval) :
-               "cc");
-  return result;
-}
-
-static inline uint
-rcr2(void)
-{
-  uint64 val;
-  asm volatile("mov %%cr2,%0" : "=r" (val));
-  return val;
-}
-
-static inline void
-lcr3(uint64 val)
-{
-  asm volatile("mov %0,%%cr3" : : "r" (val));
-}
-
-static inline void
-writegs(uint16 v)
-{
-  __asm volatile("movw %0, %%gs" : : "r" (v));
-}
-
-
-//PAGEBREAK: 36
-// Layout of the trap frame built on the stack by the
-// hardware and by trapasm.S, and passed to trap().
-struct trapframe {
-   uint64 rax;      
-   uint64 rbx;
-   uint64 rcx;
-   uint64 rdx;
-   uint64 rbp;
-   uint64 rsi;
-   uint64 rdi;
-   uint64 r8;
-   uint64 r9;
-   uint64 r10;
-   uint64 r11;
-   uint64 r12;
-   uint64 r13;
-   uint64 r14;
-   uint64 r15;
-   uint64 trapno;
-   uint64 err;
-   uint64 rip;     
-   uint16 cs;
-   uint16 padding[3];
-   uint64 rflags;  
-   uint64 rsp;     
-   uint64 ss;      
-}__attribute__((packed));
-
-struct sysframe {
-  // arguments
-  uint64 rdi;
-  uint64 rsi;
-  uint64 rdx;
-  uint64 r10;
-  uint64 r8;
-  uint64 r9;
-  
-  // callee-saved registers
-  uint64 r15;
-  uint64 r14;
-  uint64 r13;
-  uint64 r12;
-  uint64 rbx;
-  uint64 rbp;
-
-  // return value
-  uint64 rax;
-
-  // syscall registers
-  uint64 r11;   // eflags
-  uint64 rcx;   // rip
-  uint64 rsp;
-  
-}__attribute__((packed));
-
-#endif
-
-#define TF_CS 144 // offset in trapframe for saved cs