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, 0 insertions, 88 deletions

diff --git a/bootasm.S b/bootasm.S
deleted file mode 100644
index 257867c..0000000
--- a/bootasm.S
+++ /dev/null
@@ -1,88 +0,0 @@
-#include "asm.h"
-#include "memlayout.h"
-#include "mmu.h"
-
-# Start the first CPU: switch to 32-bit protected mode, jump into C.
-# The BIOS loads this code from the first sector of the hard disk into
-# memory at physical address 0x7c00 and starts executing in real mode
-# with %cs=0 %ip=7c00.
-
-.code16                       # Assemble for 16-bit mode
-.globl start
-start:
-  cli                         # BIOS enabled interrupts; disable
-
-  # Zero data segment registers DS, ES, and SS.
-  xorw    %ax,%ax             # Set %ax to zero
-  movw    %ax,%ds             # -> Data Segment
-  movw    %ax,%es             # -> Extra Segment
-  movw    %ax,%ss             # -> Stack Segment
-
-  # Physical address line A20 is tied to zero so that the first PCs 
-  # with 2 MB would run software that assumed 1 MB.  Undo that.
-seta20.1:
-  inb     $0x64,%al               # Wait for not busy
-  testb   $0x2,%al
-  jnz     seta20.1
-
-  movb    $0xd1,%al               # 0xd1 -> port 0x64
-  outb    %al,$0x64
-
-seta20.2:
-  inb     $0x64,%al               # Wait for not busy
-  testb   $0x2,%al
-  jnz     seta20.2
-
-  movb    $0xdf,%al               # 0xdf -> port 0x60
-  outb    %al,$0x60
-
-  # Switch from real to protected mode.  Use a bootstrap GDT that makes
-  # virtual addresses map directly to physical addresses so that the
-  # effective memory map doesn't change during the transition.
-  lgdt    gdtdesc
-  movl    %cr0, %eax
-  orl     $CR0_PE, %eax
-  movl    %eax, %cr0
-
-//PAGEBREAK!
-  # Complete the transition to 32-bit protected mode by using a long jmp
-  # to reload %cs and %eip.  The segment descriptors are set up with no
-  # translation, so that the mapping is still the identity mapping.
-  ljmp    $(SEG_KCODE<<3), $start32
-
-.code32  # Tell assembler to generate 32-bit code now.
-start32:
-  # Set up the protected-mode data segment registers
-  movw    $(SEG_KDATA<<3), %ax    # Our data segment selector
-  movw    %ax, %ds                # -> DS: Data Segment
-  movw    %ax, %es                # -> ES: Extra Segment
-  movw    %ax, %ss                # -> SS: Stack Segment
-  movw    $0, %ax                 # Zero segments not ready for use
-  movw    %ax, %fs                # -> FS
-  movw    %ax, %gs                # -> GS
-
-  # Set up the stack pointer and call into C.
-  movl    $start, %esp
-  call    bootmain
-
-  # If bootmain returns (it shouldn't), trigger a Bochs
-  # breakpoint if running under Bochs, then loop.
-  movw    $0x8a00, %ax            # 0x8a00 -> port 0x8a00
-  movw    %ax, %dx
-  outw    %ax, %dx
-  movw    $0x8ae0, %ax            # 0x8ae0 -> port 0x8a00
-  outw    %ax, %dx
-spin:
-  jmp     spin
-
-# Bootstrap GDT
-.p2align 2                                # force 4 byte alignment
-gdt:
-  SEG_NULLASM                             # null seg
-  SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff)   # code seg
-  SEG_ASM(STA_W, 0x0, 0xffffffff)         # data seg
-
-gdtdesc:
-  .word   (gdtdesc - gdt - 1)             # sizeof(gdt) - 1
-  .long   gdt                             # address gdt
-