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
My changes have a race with re-used bufs and the code doesn't seem to get shorter
Keep the changes that fixed ip->off race
This reverts commit 3a5fa7ed90.
Conflicts:
defs.h
file.c
file.h
Remove I_BUSY, B_BUSY, and intrans defs and usages
One spinlock per buf to avoid ugly loop in bget
fix race in filewrite (don't update f->off after releasing lock)
give cpu1 a TSS and gdt for when it enters scheduler()
and a pseudo proc[] entry for each cpu
cpu0 waits for each other cpu to start up
read() for files
wakeup1() assumes you hold proc_table_lock
sleep(chan, lock) provides atomic sleep-and-release to wait for condition
ugly code in swtch/scheduler to implement new sleep
fix lots of bugs in pipes, wait, and exit
fix bugs if timer interrupt goes off in schedule()
console locks per line, not per byte
nesting cli/sti: release shouldn't always enable interrupts
separate setup of lapic from starting of other cpus, so cpu() works earlier
flag to disable locking in console output
make locks work even when curproc==0
(still crashes in clock interrupt)
