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, 28 insertions, 10 deletions

diff --git a/usertests.c b/usertests.c
index a1e97e7..07d10d4 100644
--- a/usertests.c
+++ b/usertests.c
@@ -363,17 +363,29 @@ preempt(void)
 
   printf(1, "preempt: ");
   pid1 = fork();
+  if(pid1 < 0) {
+    printf(1, "fork failed");
+    exit();
+  }
   if(pid1 == 0)
     for(;;)
       ;
 
   pid2 = fork();
+  if(pid2 < 0) {
+    printf(1, "fork failed\n");
+    exit();
+  }
   if(pid2 == 0)
     for(;;)
       ;
 
   pipe(pfds);
   pid3 = fork();
+  if(pid3 < 0) {
+     printf(1, "fork failed\n");
+     exit();
+  }
   if(pid3 == 0){
     close(pfds[0]);
     if(write(pfds[1], "x", 1) != 1)
@@ -1391,6 +1403,11 @@ forktest(void)
       exit();
   }
 
+  if (n == 0) {
+    printf(1, "no fork at all!\n");
+    exit();
+  }
+
   if(n == 1000){
     printf(1, "fork claimed to work 1000 times!\n");
     exit();
@@ -1414,16 +1431,16 @@ forktest(void)
 void
 sbrktest(void)
 {
-  int fds[2], pid, pids[10], ppid;
-  char *a, *b, *c, *lastaddr, *oldbrk, *p, scratch;
-  uint amt;
+  int i, fds[2], pids[10], pid, ppid;
+  char *c, *oldbrk, scratch, *a, *b, *lastaddr, *p;
+  uint64 amt;
+  #define BIG (100*1024*1024)
 
   printf(stdout, "sbrk test\n");
   oldbrk = sbrk(0);
 
   // can one sbrk() less than a page?
   a = sbrk(0);
-  int i;
   for(i = 0; i < 5000; i++){
     b = sbrk(1);
     if(b != a){
@@ -1449,9 +1466,8 @@ sbrktest(void)
   wait();
 
   // can one grow address space to something big?
-#define BIG (100*1024*1024)
   a = sbrk(0);
-  amt = (BIG) - (uint)a;
+  amt = (BIG) - (uint64)a;
   p = sbrk(amt);
   if (p != a) {
     printf(stdout, "sbrk test failed to grow big address space; enough phys mem?\n");
@@ -1508,7 +1524,7 @@ sbrktest(void)
     }
     wait();
   }
-
+    
   // if we run the system out of memory, does it clean up the last
   // failed allocation?
   if(pipe(fds) != 0){
@@ -1518,7 +1534,7 @@ sbrktest(void)
   for(i = 0; i < sizeof(pids)/sizeof(pids[0]); i++){
     if((pids[i] = fork()) == 0){
       // allocate a lot of memory
-      sbrk(BIG - (uint)sbrk(0));
+      sbrk(BIG - (uint64)sbrk(0));
       write(fds[1], "x", 1);
       // sit around until killed
       for(;;) sleep(1000);
@@ -1526,6 +1542,7 @@ sbrktest(void)
     if(pids[i] != -1)
       read(fds[0], &scratch, 1);
   }
+
   // if those failed allocations freed up the pages they did allocate,
   // we'll be able to allocate here
   c = sbrk(4096);
@@ -1549,7 +1566,7 @@ sbrktest(void)
 void
 validateint(int *p)
 {
-  int res;
+  /* XXX int res;
   asm("mov %%esp, %%ebx\n\t"
       "mov %3, %%esp\n\t"
       "int %2\n\t"
@@ -1557,13 +1574,14 @@ validateint(int *p)
       "=a" (res) :
       "a" (SYS_sleep), "n" (T_SYSCALL), "c" (p) :
       "ebx");
+  */
 }
 
 void
 validatetest(void)
 {
   int hi, pid;
-  uint p;
+  uint64 p;
 
   printf(stdout, "validate test\n");
   hi = 1100*1024;