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, 13 insertions, 8 deletions

diff --git a/proc.h b/proc.h
index 1647114..5ab2de5 100644
--- a/proc.h
+++ b/proc.h
@@ -1,5 +1,8 @@
 // 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
   uchar apicid;                // Local APIC ID
   struct context *scheduler;   // swtch() here to enter scheduler
   struct taskstate ts;         // Used by x86 to find stack for interrupt
@@ -7,7 +10,6 @@ struct cpu {
   volatile uint started;       // Has the CPU started?
   int ncli;                    // Depth of pushcli nesting.
   int intena;                  // Were interrupts enabled before pushcli?
-  struct proc *proc;           // The process running on this cpu or null
 };
 
 extern struct cpu cpus[NCPU];
@@ -25,20 +27,23 @@ extern int ncpu;
 // at the "Switch stacks" comment. Switch doesn't save eip explicitly,
 // but it is on the stack and allocproc() manipulates it.
 struct context {
-  uint edi;
-  uint esi;
-  uint ebx;
-  uint ebp;
-  uint eip;
+  uint64 r15;
+  uint64 r14;
+  uint64 r13;
+  uint64 r12;
+  uint64 r11;
+  uint64 rbx;
+  uint64 ebp; //rbp
+  uint64 eip; //rip;
 };
 
 enum procstate { UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };
 
 // Per-process state
 struct proc {
-  uint sz;                     // Size of process memory (bytes)
+  char *kstack;                // Bottom of kernel stack for this process, must be first entry
+  uint64 sz;                   // Size of process memory (bytes)
   pde_t* pgdir;                // Page table
-  char *kstack;                // Bottom of kernel stack for this process
   enum procstate state;        // Process state
   int pid;                     // Process ID
   struct proc *parent;         // Parent process