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 --- syscall.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 49 insertions(+), 9 deletions(-) (limited to 'syscall.c') diff --git a/syscall.c b/syscall.c index ee85261..3ffe3d8 100644 --- a/syscall.c +++ b/syscall.c @@ -15,13 +15,13 @@ // Fetch the int at addr from the current process. int -fetchint(uint addr, int *ip) +fetchint(uint64 addr, int *ip) { struct proc *curproc = myproc(); if(addr >= curproc->sz || addr+4 > curproc->sz) return -1; - *ip = *(int*)(addr); + *ip = *(uint64*)(addr); return 0; } @@ -29,7 +29,7 @@ fetchint(uint addr, int *ip) // Doesn't actually copy the string - just sets *pp to point at it. // Returns length of string, not including nul. int -fetchstr(uint addr, char **pp) +fetchstr(uint64 addr, char **pp) { char *s, *ep; struct proc *curproc = myproc(); @@ -45,11 +45,51 @@ fetchstr(uint addr, char **pp) return -1; } +static uint64 +fetcharg(int n) +{ + struct proc *curproc = myproc(); + switch (n) { + case 0: + return curproc->tf->rdi; + case 1: + return curproc->tf->rsi; + case 2: + return curproc->tf->rdx; + case 3: + return curproc->tf->r10; + case 4: + return curproc->tf->r8; + case 5: + return curproc->tf->r9; + } + panic("fetcharg"); + return -1; +} + +int +fetchaddr(uint64 addr, uint64 *ip) +{ + struct proc *curproc = myproc(); + if(addr >= curproc->sz || addr+sizeof(uint64) > curproc->sz) + return -1; + *ip = *(uint64*)(addr); + return 0; +} + // Fetch the nth 32-bit system call argument. int argint(int n, int *ip) { - return fetchint((myproc()->tf->esp) + 4 + 4*n, ip); + *ip = fetcharg(n); + return 0; +} + +int +argaddr(int n, uint64 *ip) +{ + *ip = fetcharg(n); + return 0; } // Fetch the nth word-sized system call argument as a pointer @@ -58,10 +98,10 @@ argint(int n, int *ip) int argptr(int n, char **pp, int size) { - int i; + uint64 i; struct proc *curproc = myproc(); - if(argint(n, &i) < 0) + if(argaddr(n, &i) < 0) return -1; if(size < 0 || (uint)i >= curproc->sz || (uint)i+size > curproc->sz) return -1; @@ -134,12 +174,12 @@ syscall(void) int num; struct proc *curproc = myproc(); - num = curproc->tf->eax; + num = curproc->tf->rax; if(num > 0 && num < NELEM(syscalls) && syscalls[num]) { - curproc->tf->eax = syscalls[num](); + curproc->tf->rax = syscalls[num](); } else { cprintf("%d %s: unknown sys call %d\n", curproc->pid, curproc->name, num); - curproc->tf->eax = -1; + curproc->tf->rax = -1; } } -- cgit v1.2.3