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 --- console.c | 30 +++++++++++++++++++++++------- 1 file changed, 23 insertions(+), 7 deletions(-) (limited to 'console.c') diff --git a/console.c b/console.c index a280d2b..9986a9c 100644 --- a/console.c +++ b/console.c @@ -2,6 +2,8 @@ // Input is from the keyboard or serial port. // Output is written to the screen and serial port. +#include + #include "types.h" #include "defs.h" #include "param.h" @@ -24,10 +26,11 @@ static struct { int locking; } cons; +static char digits[] = "0123456789abcdef"; + static void printint(int xx, int base, int sign) { - static char digits[] = "0123456789abcdef"; char buf[16]; int i; uint x; @@ -48,14 +51,25 @@ printint(int xx, int base, int sign) while(--i >= 0) consputc(buf[i]); } + +static void +printptr(uint64 x) { + int i; + consputc('0'); + consputc('x'); + for (i = 0; i < (sizeof(uint64) * 2); i++, x <<= 4) + consputc(digits[x >> (sizeof(uint64) * 8 - 4)]); +} + + //PAGEBREAK: 50 // Print to the console. only understands %d, %x, %p, %s. void cprintf(char *fmt, ...) { + va_list ap; int i, c, locking; - uint *argp; char *s; locking = cons.locking; @@ -65,7 +79,7 @@ cprintf(char *fmt, ...) if (fmt == 0) panic("null fmt"); - argp = (uint*)(void*)(&fmt + 1); + va_start(ap, fmt); for(i = 0; (c = fmt[i] & 0xff) != 0; i++){ if(c != '%'){ consputc(c); @@ -76,14 +90,16 @@ cprintf(char *fmt, ...) break; switch(c){ case 'd': - printint(*argp++, 10, 1); + printint(va_arg(ap, int), 10, 1); break; case 'x': + printint(va_arg(ap, int), 16, 1); + break; case 'p': - printint(*argp++, 16, 0); + printptr(va_arg(ap, uint64)); break; case 's': - if((s = (char*)*argp++) == 0) + if((s = va_arg(ap, char*)) == 0) s = "(null)"; for(; *s; s++) consputc(*s); @@ -107,7 +123,7 @@ void panic(char *s) { int i; - uint pcs[10]; + uint64 pcs[10]; cli(); cons.locking = 0; -- cgit v1.2.3