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 --- usertests.c | 38 ++++++++++++++++++++++++++++---------- 1 file changed, 28 insertions(+), 10 deletions(-) (limited to 'usertests.c') diff --git a/usertests.c b/usertests.c index a1e97e7..07d10d4 100644 --- a/usertests.c +++ b/usertests.c @@ -363,17 +363,29 @@ preempt(void) printf(1, "preempt: "); pid1 = fork(); + if(pid1 < 0) { + printf(1, "fork failed"); + exit(); + } if(pid1 == 0) for(;;) ; pid2 = fork(); + if(pid2 < 0) { + printf(1, "fork failed\n"); + exit(); + } if(pid2 == 0) for(;;) ; pipe(pfds); pid3 = fork(); + if(pid3 < 0) { + printf(1, "fork failed\n"); + exit(); + } if(pid3 == 0){ close(pfds[0]); if(write(pfds[1], "x", 1) != 1) @@ -1391,6 +1403,11 @@ forktest(void) exit(); } + if (n == 0) { + printf(1, "no fork at all!\n"); + exit(); + } + if(n == 1000){ printf(1, "fork claimed to work 1000 times!\n"); exit(); @@ -1414,16 +1431,16 @@ forktest(void) void sbrktest(void) { - int fds[2], pid, pids[10], ppid; - char *a, *b, *c, *lastaddr, *oldbrk, *p, scratch; - uint amt; + int i, fds[2], pids[10], pid, ppid; + char *c, *oldbrk, scratch, *a, *b, *lastaddr, *p; + uint64 amt; + #define BIG (100*1024*1024) printf(stdout, "sbrk test\n"); oldbrk = sbrk(0); // can one sbrk() less than a page? a = sbrk(0); - int i; for(i = 0; i < 5000; i++){ b = sbrk(1); if(b != a){ @@ -1449,9 +1466,8 @@ sbrktest(void) wait(); // can one grow address space to something big? -#define BIG (100*1024*1024) a = sbrk(0); - amt = (BIG) - (uint)a; + amt = (BIG) - (uint64)a; p = sbrk(amt); if (p != a) { printf(stdout, "sbrk test failed to grow big address space; enough phys mem?\n"); @@ -1508,7 +1524,7 @@ sbrktest(void) } wait(); } - + // if we run the system out of memory, does it clean up the last // failed allocation? if(pipe(fds) != 0){ @@ -1518,7 +1534,7 @@ sbrktest(void) for(i = 0; i < sizeof(pids)/sizeof(pids[0]); i++){ if((pids[i] = fork()) == 0){ // allocate a lot of memory - sbrk(BIG - (uint)sbrk(0)); + sbrk(BIG - (uint64)sbrk(0)); write(fds[1], "x", 1); // sit around until killed for(;;) sleep(1000); @@ -1526,6 +1542,7 @@ sbrktest(void) if(pids[i] != -1) read(fds[0], &scratch, 1); } + // if those failed allocations freed up the pages they did allocate, // we'll be able to allocate here c = sbrk(4096); @@ -1549,7 +1566,7 @@ sbrktest(void) void validateint(int *p) { - int res; + /* XXX int res; asm("mov %%esp, %%ebx\n\t" "mov %3, %%esp\n\t" "int %2\n\t" @@ -1557,13 +1574,14 @@ validateint(int *p) "=a" (res) : "a" (SYS_sleep), "n" (T_SYSCALL), "c" (p) : "ebx"); + */ } void validatetest(void) { int hi, pid; - uint p; + uint64 p; printf(stdout, "validate test\n"); hi = 1100*1024; -- cgit v1.2.3