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, 18 insertions, 11 deletions

diff --git a/trap.c b/trap.c
index 41c66eb..f27b99b 100644
--- a/trap.c
+++ b/trap.c
@@ -9,8 +9,8 @@
 #include "spinlock.h"
 
 // Interrupt descriptor table (shared by all CPUs).
-struct gatedesc idt[256];
-extern uint vectors[];  // in vectors.S: array of 256 entry pointers
+struct intgate idt[256];
+extern uint64 vectors[];  // in vectors.S: array of 256 entry pointers
 struct spinlock tickslock;
 uint ticks;
 
@@ -19,17 +19,22 @@ tvinit(void)
 {
   int i;
 
-  for(i = 0; i < 256; i++)
-    SETGATE(idt[i], 0, SEG_KCODE<<3, vectors[i], 0);
-  SETGATE(idt[T_SYSCALL], 1, SEG_KCODE<<3, vectors[T_SYSCALL], DPL_USER);
-
+  for(i=0; i<256; i++) {
+    idt[i] = INTDESC(KCSEG, vectors[i], INT_P | SEG_INTR64);
+  }
+  idtinit();
+    
   initlock(&tickslock, "time");
 }
 
 void
 idtinit(void)
 {
-  lidt(idt, sizeof(idt));
+  struct desctr dtr;
+
+  dtr.limit = sizeof(idt) - 1;
+  dtr.base = (uint64)idt;
+  lidt((void *)&dtr.limit);
 }
 
 //PAGEBREAK: 41
@@ -74,7 +79,7 @@ trap(struct trapframe *tf)
   case T_IRQ0 + 7:
   case T_IRQ0 + IRQ_SPURIOUS:
     cprintf("cpu%d: spurious interrupt at %x:%x\n",
-            cpuid(), tf->cs, tf->eip);
+            cpuid(), tf->cs, tf->rip);
     lapiceoi();
     break;
 
@@ -83,14 +88,14 @@ trap(struct trapframe *tf)
     if(myproc() == 0 || (tf->cs&3) == 0){
       // In kernel, it must be our mistake.
       cprintf("unexpected trap %d from cpu %d eip %x (cr2=0x%x)\n",
-              tf->trapno, cpuid(), tf->eip, rcr2());
+              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 "
             "eip 0x%x addr 0x%x--kill proc\n",
             myproc()->pid, myproc()->name, tf->trapno,
-            tf->err, cpuid(), tf->eip, rcr2());
+            tf->err, cpuid(), tf->rip, rcr2());
     myproc()->killed = 1;
   }
 
@@ -105,8 +110,10 @@ trap(struct trapframe *tf)
   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();
 }
+
+