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 --- trap.c | 29 ++++++++++++++++++----------- 1 file changed, 18 insertions(+), 11 deletions(-) (limited to 'trap.c') diff --git a/trap.c b/trap.c index 41c66eb..f27b99b 100644 --- a/trap.c +++ b/trap.c @@ -9,8 +9,8 @@ #include "spinlock.h" // Interrupt descriptor table (shared by all CPUs). -struct gatedesc idt[256]; -extern uint vectors[]; // in vectors.S: array of 256 entry pointers +struct intgate idt[256]; +extern uint64 vectors[]; // in vectors.S: array of 256 entry pointers struct spinlock tickslock; uint ticks; @@ -19,17 +19,22 @@ tvinit(void) { int i; - for(i = 0; i < 256; i++) - SETGATE(idt[i], 0, SEG_KCODE<<3, vectors[i], 0); - SETGATE(idt[T_SYSCALL], 1, SEG_KCODE<<3, vectors[T_SYSCALL], DPL_USER); - + for(i=0; i<256; i++) { + idt[i] = INTDESC(KCSEG, vectors[i], INT_P | SEG_INTR64); + } + idtinit(); + initlock(&tickslock, "time"); } void idtinit(void) { - lidt(idt, sizeof(idt)); + struct desctr dtr; + + dtr.limit = sizeof(idt) - 1; + dtr.base = (uint64)idt; + lidt((void *)&dtr.limit); } //PAGEBREAK: 41 @@ -74,7 +79,7 @@ trap(struct trapframe *tf) case T_IRQ0 + 7: case T_IRQ0 + IRQ_SPURIOUS: cprintf("cpu%d: spurious interrupt at %x:%x\n", - cpuid(), tf->cs, tf->eip); + cpuid(), tf->cs, tf->rip); lapiceoi(); break; @@ -83,14 +88,14 @@ trap(struct trapframe *tf) if(myproc() == 0 || (tf->cs&3) == 0){ // In kernel, it must be our mistake. cprintf("unexpected trap %d from cpu %d eip %x (cr2=0x%x)\n", - tf->trapno, cpuid(), tf->eip, rcr2()); + tf->trapno, cpuid(), tf->rip, rcr2()); panic("trap"); } // In user space, assume process misbehaved. cprintf("pid %d %s: trap %d err %d on cpu %d " "eip 0x%x addr 0x%x--kill proc\n", myproc()->pid, myproc()->name, tf->trapno, - tf->err, cpuid(), tf->eip, rcr2()); + tf->err, cpuid(), tf->rip, rcr2()); myproc()->killed = 1; } @@ -105,8 +110,10 @@ trap(struct trapframe *tf) if(myproc() && myproc()->state == RUNNING && tf->trapno == T_IRQ0+IRQ_TIMER) yield(); - + // Check if the process has been killed since we yielded if(myproc() && myproc()->killed && (tf->cs&3) == DPL_USER) exit(); } + + -- cgit v1.2.3