From ab0db651af6f1ffa8fe96909ce16ae314d65c3fb Mon Sep 17 00:00:00 2001 From: Frans Kaashoek Date: Sun, 23 Sep 2018 08:24:42 -0400 Subject: 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 --- proc.c | 34 ++++++++++++++++------------------ 1 file changed, 16 insertions(+), 18 deletions(-) (limited to 'proc.c') diff --git a/proc.c b/proc.c index 806b1b1..58ae948 100644 --- a/proc.c +++ b/proc.c @@ -6,6 +6,7 @@ #include "x86.h" #include "proc.h" #include "spinlock.h" +#include "msr.h" struct { struct spinlock lock; @@ -16,7 +17,7 @@ static struct proc *initproc; int nextpid = 1; extern void forkret(void); -extern void trapret(void); +extern void sysexit(void); static void wakeup1(void *chan); @@ -104,13 +105,13 @@ found: // Set up new context to start executing at forkret, // which returns to trapret. - sp -= 4; - *(uint*)sp = (uint)trapret; + sp -= sizeof(uint64); + *(uint64*)sp = (uint64)sysexit; sp -= sizeof *p->context; p->context = (struct context*)sp; memset(p->context, 0, sizeof *p->context); - p->context->eip = (uint)forkret; + p->context->eip = (uint64)forkret; return p; } @@ -128,16 +129,12 @@ userinit(void) initproc = p; if((p->pgdir = setupkvm()) == 0) panic("userinit: out of memory?"); - inituvm(p->pgdir, _binary_initcode_start, (int)_binary_initcode_size); + inituvm(p->pgdir, _binary_initcode_start, (uint64)_binary_initcode_size); p->sz = PGSIZE; memset(p->tf, 0, sizeof(*p->tf)); - p->tf->cs = (SEG_UCODE << 3) | DPL_USER; - p->tf->ds = (SEG_UDATA << 3) | DPL_USER; - p->tf->es = p->tf->ds; - p->tf->ss = p->tf->ds; - p->tf->eflags = FL_IF; - p->tf->esp = PGSIZE; - p->tf->eip = 0; // beginning of initcode.S + p->tf->r11 = FL_IF; + p->tf->rsp = PGSIZE; + p->tf->rcx = 0; // beginning of initcode.S safestrcpy(p->name, "initcode", sizeof(p->name)); p->cwd = namei("/"); @@ -201,7 +198,7 @@ fork(void) *np->tf = *curproc->tf; // Clear %eax so that fork returns 0 in the child. - np->tf->eax = 0; + np->tf->rax = 0; for(i = 0; i < NOFILE; i++) if(curproc->ofile[i]) @@ -289,8 +286,8 @@ wait(void) pid = p->pid; kfree(p->kstack); p->kstack = 0; - freevm(p->pgdir); - p->pid = 0; + freevm(p->pgdir, p->sz); + p->pid = 0; p->parent = 0; p->name[0] = 0; p->killed = 0; @@ -339,6 +336,7 @@ scheduler(void) // Switch to chosen process. It is the process's job // to release ptable.lock and then reacquire it // before jumping back to us. + c->proc = p; switchuvm(p); p->state = RUNNING; @@ -408,7 +406,7 @@ forkret(void) iinit(ROOTDEV); initlog(ROOTDEV); } - + // Return to "caller", actually trapret (see allocproc). } @@ -514,7 +512,7 @@ procdump(void) int i; struct proc *p; char *state; - uint pc[10]; + uint64 pc[10]; for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){ if(p->state == UNUSED) @@ -525,7 +523,7 @@ procdump(void) state = "???"; cprintf("%d %s %s", p->pid, state, p->name); if(p->state == SLEEPING){ - getcallerpcs((uint*)p->context->ebp+2, pc); + getcallerpcs((uint64*)p->context->ebp+2, pc); for(i=0; i<10 && pc[i] != 0; i++) cprintf(" %p", pc[i]); } -- cgit v1.2.3