Checkpoint port of xv6 to x86-64. Passed usertests on 2 processors a few times.

The x86-64 doesn't just add two levels to page tables to support 64 bit
addresses, but is a different processor. For example, calling conventions,
system calls, and segmentation are different from 32-bit x86. Segmentation is
basically gone, but gs/fs in combination with MSRs can be used to hold a
per-core pointer. In general, x86-64 is more straightforward than 32-bit
x86. The port uses code from sv6 and the xv6 "rsc-amd64" branch.

A summary of the changes is as follows:

- Booting: switch to grub instead of xv6's bootloader (pass -kernel to qemu),
because xv6's boot loader doesn't understand 64bit ELF files.  And, we don't
care anymore about booting.

- Makefile: use -m64 instead of -m32 flag for gcc, delete boot loader, xv6.img,
bochs, and memfs. For now dont' use -O2, since usertests with -O2 is bigger than
MAXFILE!

- Update gdb.tmpl to be for i386 or x86-64

- Console/printf: use stdarg.h and treat 64-bit addresses different from ints
  (32-bit)

- Update elfhdr to be 64 bit

- entry.S/entryother.S: add code to switch to 64-bit mode: build a simple page
table in 32-bit mode before switching to 64-bit mode, share code for entering
boot processor and APs, and tweak boot gdt.  The boot gdt is the gdt that the
kernel proper also uses. (In 64-bit mode, the gdt/segmentation and task state
mostly disappear.)

- exec.c: fix passing argv (64-bit now instead of 32-bit).

- initcode.c: use syscall instead of int.

- kernel.ld: load kernel very high, in top terabyte.  64 bits is a lot of
address space!

- proc.c: initial return is through new syscall path instead of trapret.

- proc.h: update struct cpu to have some scratch space since syscall saves less
state than int, update struct context to reflect x86-64 calling conventions.

- swtch: simplify for x86-64 calling conventions.

- syscall: add fetcharg to handle x86-64 calling convetions (6 arguments are
passed through registers), and fetchaddr to read a 64-bit value from user space.

- sysfile: update to handle pointers from user space (e.g., sys_exec), which are
64 bits.

- trap.c: no special trap vector for sys calls, because x86-64 has a different
plan for system calls.

- trapasm: one plan for syscalls and one plan for traps (interrupt and
exceptions). On x86-64, the kernel is responsible for switching user/kernel
stacks. To do, xv6 keeps some scratch space in the cpu structure, and uses MSR
GS_KERN_BASE to point to the core's cpu structure (using swapgs).

- types.h: add uint64, and change pde_t to uint64

- usertests: exit() when fork fails, which helped in tracking down one of the
bugs in the switch from 32-bit to 64-bit

- vectors: update to make them 64 bits

- vm.c: use bootgdt in kernel too, program MSRs for syscalls and core-local
state (for swapgs), walk 4 levels in walkpgdir, add DEVSPACETOP, use task
segment to set kernel stack for interrupts (but simpler than in 32-bit mode),
add an extra argument to freevm (size of user part of address space) to avoid
checking all entries till KERNBASE (there are MANY TB before the top 1TB).

- x86: update trapframe to have 64-bit entries, which is what the processor
pushes on syscalls and traps.  simplify lgdt and lidt, using struct desctr,
which needs the gcc directives packed and aligned.

TODO:
- use int32 instead of int?
- simplify curproc(). xv6 has per-cpu state again, but this time it must have it.
- avoid repetition in walkpgdir
- fix validateint() in usertests.c
- fix bugs (e.g., observed one a case of entering kernel with invalid gs or proc

1 files changed, 23 insertions, 7 deletions

diff --git a/console.c b/console.c
index a280d2b..9986a9c 100644
--- a/console.c
+++ b/console.c
@@ -2,6 +2,8 @@
 // Input is from the keyboard or serial port.
 // Output is written to the screen and serial port.
 
+#include <stdarg.h>
+
 #include "types.h"
 #include "defs.h"
 #include "param.h"
@@ -24,10 +26,11 @@ static struct {
   int locking;
 } cons;
 
+static char digits[] = "0123456789abcdef";
+
 static void
 printint(int xx, int base, int sign)
 {
-  static char digits[] = "0123456789abcdef";
   char buf[16];
   int i;
   uint x;
@@ -48,14 +51,25 @@ printint(int xx, int base, int sign)
   while(--i >= 0)
     consputc(buf[i]);
 }
+
+static void
+printptr(uint64 x) {
+  int i;
+  consputc('0');
+  consputc('x');
+  for (i = 0; i < (sizeof(uint64) * 2); i++, x <<= 4)
+    consputc(digits[x >> (sizeof(uint64) * 8 - 4)]);
+}
+
+
 //PAGEBREAK: 50
 
 // Print to the console. only understands %d, %x, %p, %s.
 void
 cprintf(char *fmt, ...)
 {
+  va_list ap;
   int i, c, locking;
-  uint *argp;
   char *s;
 
   locking = cons.locking;
@@ -65,7 +79,7 @@ cprintf(char *fmt, ...)
   if (fmt == 0)
     panic("null fmt");
 
-  argp = (uint*)(void*)(&fmt + 1);
+  va_start(ap, fmt);
   for(i = 0; (c = fmt[i] & 0xff) != 0; i++){
     if(c != '%'){
       consputc(c);
@@ -76,14 +90,16 @@ cprintf(char *fmt, ...)
       break;
     switch(c){
     case 'd':
-      printint(*argp++, 10, 1);
+      printint(va_arg(ap, int), 10, 1);
       break;
     case 'x':
+      printint(va_arg(ap, int), 16, 1);
+      break;
     case 'p':
-      printint(*argp++, 16, 0);
+      printptr(va_arg(ap, uint64));
       break;
     case 's':
-      if((s = (char*)*argp++) == 0)
+      if((s = va_arg(ap, char*)) == 0)
         s = "(null)";
       for(; *s; s++)
         consputc(*s);
@@ -107,7 +123,7 @@ void
 panic(char *s)
 {
   int i;
-  uint pcs[10];
+  uint64 pcs[10];
 
   cli();
   cons.locking = 0;