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 --- exec.c | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) (limited to 'exec.c') diff --git a/exec.c b/exec.c index b40134f..b1a9229 100644 --- a/exec.c +++ b/exec.c @@ -4,6 +4,8 @@ #include "mmu.h" #include "proc.h" #include "defs.h" +#include "traps.h" +#include "msr.h" #include "x86.h" #include "elf.h" @@ -12,18 +14,18 @@ exec(char *path, char **argv) { char *s, *last; int i, off; - uint argc, sz, sp, ustack[3+MAXARG+1]; + uint64 argc, sz, sp, ustack[3+MAXARG+1]; struct elfhdr elf; struct inode *ip; struct proghdr ph; pde_t *pgdir, *oldpgdir; struct proc *curproc = myproc(); - + uint64 oldsz = curproc->sz; + begin_op(); if((ip = namei(path)) == 0){ end_op(); - cprintf("exec: fail\n"); return -1; } ilock(ip); @@ -72,7 +74,7 @@ exec(char *path, char **argv) for(argc = 0; argv[argc]; argc++) { if(argc >= MAXARG) goto bad; - sp = (sp - (strlen(argv[argc]) + 1)) & ~3; + sp = (sp - (strlen(argv[argc]) + 1)) & ~(sizeof(uint64)-1); if(copyout(pgdir, sp, argv[argc], strlen(argv[argc]) + 1) < 0) goto bad; ustack[3+argc] = sp; @@ -81,10 +83,13 @@ exec(char *path, char **argv) ustack[0] = 0xffffffff; // fake return PC ustack[1] = argc; - ustack[2] = sp - (argc+1)*4; // argv pointer + ustack[2] = sp - (argc+1)*sizeof(uint64); // argv pointer + + curproc->tf->rdi = argc; + curproc->tf->rsi = sp - (argc+1)*sizeof(uint64); - sp -= (3+argc+1) * 4; - if(copyout(pgdir, sp, ustack, (3+argc+1)*4) < 0) + sp -= (3+argc+1) * sizeof(uint64); + if(copyout(pgdir, sp, ustack, (3+argc+1)*sizeof(uint64)) < 0) goto bad; // Save program name for debugging. @@ -92,20 +97,21 @@ exec(char *path, char **argv) if(*s == '/') last = s+1; safestrcpy(curproc->name, last, sizeof(curproc->name)); - + // Commit to the user image. oldpgdir = curproc->pgdir; curproc->pgdir = pgdir; curproc->sz = sz; - curproc->tf->eip = elf.entry; // main - curproc->tf->esp = sp; + curproc->tf->rip = elf.entry; // main + curproc->tf->rcx = elf.entry; + curproc->tf->rsp = sp; switchuvm(curproc); - freevm(oldpgdir); + freevm(oldpgdir, oldsz); return 0; bad: if(pgdir) - freevm(pgdir); + freevm(pgdir, sz); if(ip){ iunlockput(ip); end_op(); -- cgit v1.2.3