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, 22 insertions, 57 deletions

diff --git a/Makefile b/Makefile
index 09d790c..b199842 100644
--- a/Makefile
+++ b/Makefile
@@ -51,7 +51,7 @@ TOOLPREFIX := $(shell if i386-jos-elf-objdump -i 2>&1 | grep '^elf32-i386$$' >/d
 endif
 
 # If the makefile can't find QEMU, specify its path here
-# QEMU = qemu-system-i386
+QEMU = qemu-system-x86_64
 
 # Try to infer the correct QEMU
 ifndef QEMU
@@ -76,11 +76,16 @@ AS = $(TOOLPREFIX)gas
 LD = $(TOOLPREFIX)ld
 OBJCOPY = $(TOOLPREFIX)objcopy
 OBJDUMP = $(TOOLPREFIX)objdump
-CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -O2 -Wall -MD -ggdb -m32 -Werror -fno-omit-frame-pointer
+
+XFLAGS = -m64 -mcmodel=large -ggdb
+# CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -O2 -Wall -MD -ggdb -Werror -fno-omit-frame-pointer
+CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -Wall -MD -ggdb -Werror -fno-omit-frame-pointer
+CFLAGS += -ffreestanding -fno-common -nostdlib $(XFLAGS)
 CFLAGS += $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
-ASFLAGS = -m32 -gdwarf-2 -Wa,-divide
+ASFLAGS = -gdwarf-2 -Wa,-divide $(XFLAGS)
 # FreeBSD ld wants ``elf_i386_fbsd''
-LDFLAGS += -m $(shell $(LD) -V | grep elf_i386 2>/dev/null | head -n 1)
+LDFLAGS += -m $(shell $(LD) -V | grep elf_x86_64 2>/dev/null | head -n 1)
+LDFLAGS += -z max-page-size=4096
 
 # Disable PIE when possible (for Ubuntu 16.10 toolchain)
 ifneq ($(shell $(CC) -dumpspecs 2>/dev/null | grep -e '[^f]no-pie'),)
@@ -90,23 +95,10 @@ ifneq ($(shell $(CC) -dumpspecs 2>/dev/null | grep -e '[^f]nopie'),)
 CFLAGS += -fno-pie -nopie
 endif
 
-xv6.img: bootblock kernel
-	dd if=/dev/zero of=xv6.img count=10000
-	dd if=bootblock of=xv6.img conv=notrunc
-	dd if=kernel of=xv6.img seek=1 conv=notrunc
-
-xv6memfs.img: bootblock kernelmemfs
-	dd if=/dev/zero of=xv6memfs.img count=10000
-	dd if=bootblock of=xv6memfs.img conv=notrunc
-	dd if=kernelmemfs of=xv6memfs.img seek=1 conv=notrunc
-
-bootblock: bootasm.S bootmain.c
-	$(CC) $(CFLAGS) -fno-pic -O -nostdinc -I. -c bootmain.c
-	$(CC) $(CFLAGS) -fno-pic -nostdinc -I. -c bootasm.S
-	$(LD) $(LDFLAGS) -N -e start -Ttext 0x7C00 -o bootblock.o bootasm.o bootmain.o
-	$(OBJDUMP) -S bootblock.o > bootblock.asm
-	$(OBJCOPY) -S -O binary -j .text bootblock.o bootblock
-	./sign.pl bootblock
+kernel: $(OBJS) entry.o entryother initcode kernel.ld
+	$(LD) $(LDFLAGS) -T kernel.ld -o kernel entry.o $(OBJS) -b binary initcode entryother
+	$(OBJDUMP) -S kernel > kernel.asm
+	$(OBJDUMP) -t kernel | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > kernel.sym
 
 entryother: entryother.S
 	$(CC) $(CFLAGS) -fno-pic -nostdinc -I. -c entryother.S
@@ -120,23 +112,6 @@ initcode: initcode.S
 	$(OBJCOPY) -S -O binary initcode.out initcode
 	$(OBJDUMP) -S initcode.o > initcode.asm
 
-kernel: $(OBJS) entry.o entryother initcode kernel.ld
-	$(LD) $(LDFLAGS) -T kernel.ld -o kernel entry.o $(OBJS) -b binary initcode entryother
-	$(OBJDUMP) -S kernel > kernel.asm
-	$(OBJDUMP) -t kernel | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > kernel.sym
-
-# kernelmemfs is a copy of kernel that maintains the
-# disk image in memory instead of writing to a disk.
-# This is not so useful for testing persistent storage or
-# exploring disk buffering implementations, but it is
-# great for testing the kernel on real hardware without
-# needing a scratch disk.
-MEMFSOBJS = $(filter-out ide.o,$(OBJS)) memide.o
-kernelmemfs: $(MEMFSOBJS) entry.o entryother initcode kernel.ld fs.img
-	$(LD) $(LDFLAGS) -T kernel.ld -o kernelmemfs entry.o  $(MEMFSOBJS) -b binary initcode entryother fs.img
-	$(OBJDUMP) -S kernelmemfs > kernelmemfs.asm
-	$(OBJDUMP) -t kernelmemfs | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > kernelmemfs.sym
-
 tags: $(OBJS) entryother.S _init
 	etags *.S *.c
 
@@ -190,8 +165,8 @@ fs.img: mkfs README $(UPROGS)
 clean: 
 	rm -f *.tex *.dvi *.idx *.aux *.log *.ind *.ilg \
 	*.o *.d *.asm *.sym vectors.S bootblock entryother \
-	initcode initcode.out kernel xv6.img fs.img kernelmemfs \
-	xv6memfs.img mkfs .gdbinit \
+	initcode initcode.out kernel fs.img kernelmemfs \
+	mkfs .gdbinit \
 	$(UPROGS)
 
 # make a printout
@@ -204,12 +179,6 @@ xv6.pdf: $(PRINT)
 
 print: xv6.pdf
 
-# run in emulators
-
-bochs : fs.img xv6.img
-	if [ ! -e .bochsrc ]; then ln -s dot-bochsrc .bochsrc; fi
-	bochs -q
-
 # try to generate a unique GDB port
 GDBPORT = $(shell expr `id -u` % 5000 + 25000)
 # QEMU's gdb stub command line changed in 0.11
@@ -219,25 +188,21 @@ QEMUGDB = $(shell if $(QEMU) -help | grep -q '^-gdb'; \
 ifndef CPUS
 CPUS := 2
 endif
-QEMUOPTS = -drive file=fs.img,index=1,media=disk,format=raw -drive file=xv6.img,index=0,media=disk,format=raw -smp $(CPUS) -m 512 $(QEMUEXTRA)
-
-qemu: fs.img xv6.img
+QEMUOPTS = -kernel kernel -drive file=fs.img,index=1,media=disk,format=raw -smp $(CPUS) -m 512 $(QEMUEXTRA)
+qemu: fs.img
 	$(QEMU) -serial mon:stdio $(QEMUOPTS)
 
-qemu-memfs: xv6memfs.img
-	$(QEMU) -drive file=xv6memfs.img,index=0,media=disk,format=raw -smp $(CPUS) -m 256
-
-qemu-nox: fs.img xv6.img
+qemu-nox: fs.img kernel
 	$(QEMU) -nographic $(QEMUOPTS)
 
-.gdbinit: .gdbinit.tmpl
+.gdbinit: .gdbinit.tmpl-x64
 	sed "s/localhost:1234/localhost:$(GDBPORT)/" < $^ > $@
 
-qemu-gdb: fs.img xv6.img .gdbinit
+qemu-gdb: fs.img kernel .gdbinit
 	@echo "*** Now run 'gdb'." 1>&2
-	$(QEMU) -serial mon:stdio $(QEMUOPTS) -S $(QEMUGDB)
+	$(QEMU) $(QEMUOPTS) -S $(QEMUGDB)
 
-qemu-nox-gdb: fs.img xv6.img .gdbinit
+qemu-nox-gdb: fs.img kernel .gdbinit
 	@echo "*** Now run 'gdb'." 1>&2
 	$(QEMU) -nographic $(QEMUOPTS) -S $(QEMUGDB)