LAB 2 CSE 660 Submitted By: Arumugam Thendramil Pavai

Transcription

1 LAB 2 CSE 660 Submitted By: Arumugam Thendramil Pavai Steps to install Xv6 in CentOS 7 Copied the source code by using the git clone command, git clone git://github.com/mit-pdos/xv6-public.git Copied to a folder named lab2 cp -r xv6-public/ Documents/lab2 Installed QEMU using the following commands [root@localhost qemu]# git clonegit://git.qemu-project.org/qemu.git [root@localhost qemu]#./configure [root@localhost qemu]# make [root@localhost qemu]# make install Found the Path for QEMU using 'which' command [root@localhost qemu]# which qemu-system-i386 /usr/local/bin/qemu-system-i386

2 In the Makefile for Xv6 changed the path for QEMU QEMU = /usr/local/bin/qemu-system-i386 open terminal in lab2 folder which contains files for Xv6 Script for running Xv6 [root@localhost lab2]# make qemu-nox dd if=/dev/zero of=xv6.img count= records in records out bytes (5.1 MB) copied, s, 53.5 MB/s dd if=bootblock of=xv6.img conv=notrunc 1+0 records in 1+0 records out 512 bytes (512 B) copied, s, 348 kb/s dd if=kernel of=xv6.img seek=1 conv=notrunc records in records out bytes (181 kb) copied, s, 3.0 MB/s /usr/local/bin/qemu-system-i386 -nographic -drive file=fs.img,index=1,media=disk,format=raw -drive file=xv6.img,index=0,media=disk,format=raw -smp 2 -m 512 xv6... cpu1: starting cpu0: starting sb: size 1000 nblocks 941 ninodes 200 nlog 30 logstart 2 inodestart 32 bmap start 58 init: starting sh $ ls README cat echo forktest grep init kill ln ls mkdir rm sh stressfs usertests wc zombie console myfile myfile $ echo cse 660

3 cse 660 $ cat README xv6 is a re-implementation of Dennis Ritchie's and Ken Thompson's Unix Version 6 (v6). xv6 loosely follows the structure and style of v6, but is implemented for a modern x86-based multiprocessor using ANSI C. ACKNOWLEDGMENTS xv6 is inspired by John Lions's Commentary on UNIX 6th Edition (Peer to Peer Communications; ISBN: ; 1st edition (June 14, 2000)). See also which provides pointers to on-line resources for v6. xv6 borrows code from the following sources: JOS (asm.h, elf.h, mmu.h, bootasm.s, ide.c, console.c, and others) Plan 9 (entryother.s, mp.h, mp.c, lapic.c) FreeBSD (ioapic.c) NetBSD (console.c) The following people have made contributions: Russ Cox (context switching, locking), Cliff Frey (MP), Xiao Yu (MP), Nickolai Zeldovich, and Austin Clements. We are also grateful for the bug reports and patches contributed by Silas Boyd-Wickizer, Cody Cutler, Mike CAT, Nelson Elhage, Nathaniel Filardo, Peter Froehlich, Yakir Goaron, Shivam Handa, Bryan Henry, Jim Huang, Anders Kaseorg, kehao95, Wolfgang Keller, Eddie Kohler, Imbar Marinescu, Yandong Mao, Hitoshi Mitake, Carmi Merimovich, Joel Nider, Greg Price, Ayan Shafqat, Eldar Sehayek, Yongming Shen, Cam Tenny, Rafael Ubal, Warren Toomey, Stephen Tu, Pablo Ventura, Xi Wang, Keiichi Watanabe, Nicolas Wolovick, Jindong Zhang, and Zou Chang Wei. The code in the files that constitute xv6 is Copyright Frans Kaashoek, Robert Morris, and Russ Cox. ERROR REPORTS If you spot errors or have suggestions for improvement, please send to Frans Kaashoek and Robert Morris (kaashoek,rtm@csail.mit.edu). If you have suggestions for improvements, please keep in mind that the main purpose of xv6 is as a teaching operating system for MIT's For example, we are in particular interested in simplifications and clarifications, instead of suggestions for new systems calls, more portability, etc. BUILDING AND RUNNING XV6

4 To build xv6 on an x86 ELF machine (like Linux or FreeBSD), run "make". On non-x86 or non-elf machines (like OS X, even on x86), you will need to install a cross-compiler gcc suite capable of producing x86 ELF binaries. See Then run "make TOOLPREFIX=i386-jos-elf-". To run xv6, install the QEMU PC simulators. To run in QEMU, run "make qemu". To create a typeset version of the code, run "make xv6.pdf". This requires the "mpage" utility. See $ grep os README Version 6 (v6). xv6 loosely follows the structure and style of v6, 2000)). See also which kehao95, Wolfgang Keller, Eddie Kohler, Imbar Marinescu, Yandong Mao, Hitoshi suggestions for improvements, please keep in mind that the main purpose of xv6 need to install a cross-compiler gcc suite capable of producing x86 ELF binaries. See Then run "make TOOLPREFIX=i386-jos-elf-". $ cat README grep os wc $ echo cse 660 lab report > myfile $ cat myfile cse 660 lab report Learning and Observations: Ran various commands like ls, echo, cat, grep in Xv6. All commands seems to work same as basic linux commands. =================================================================================== Answer a) Debugging GDB [root@localhost lab2]# make qemu-nox-gdb dd if=/dev/zero of=xv6.img count= records in records out bytes (5.1 MB) copied, s, 79.6 MB/s dd if=bootblock of=xv6.img conv=notrunc 1+0 records in 1+0 records out 512 bytes (512 B) copied, s, 390 kb/s dd if=kernel of=xv6.img seek=1 conv=notrunc records in records out bytes (181 kb) copied, s, 6.7 MB/s sed "s/localhost:1234/localhost:25000/" <.gdbinit.tmpl >.gdbinit

5 *** Now run 'gdb'. /usr/local/bin/qemu-system-i386 -nographic -drive file=fs.img,index=1,media=disk,format=raw -drive file=xv6.img,index=0,media=disk,format=raw -smp 2 -m 512 -S -gdb tcp::25000 ============================================================================== Remote to XV6 [root@localhost lab2]# gdb GNU gdb (GDB) Red Hat Enterprise Linux el7 Copyright (C) 2013 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later < This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-redhat-linux-gnu". For bug reporting instructions, please see: < warning: File "/root/documents/lab2/.gdbinit" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/autoload:/usr/bin/mono-gdb.py". To enable execution of this file add add-auto-load-safe-path /root/documents/lab2/.gdbinit line to your configuration file "/root/.gdbinit". To completely disable this security protection add set auto-load safe-path / line to your configuration file "/root/.gdbinit". For more information about this security protection see the "Auto-loading safe path" section in the GDB manual. E.g., run from the shell: info "(gdb)auto-loading safe path" (gdb) target remote : Remote debugging using : x0000fff0 in?? () (gdb) file kernel A program is being debugged already. Are you sure you want to change the file? (y or n) y Reading symbols from /root/documents/lab2/kernel...done. (gdb) break swtch Breakpoint 1 at 0x b: file swtch.s, line 10. Breakpoint 1, swtch () at swtch.s:10 10 movl 4(%esp), %eax 11 movl 8(%esp), %edx 14 pushl %ebp swtch () at swtch.s:15

6 15 pushl %ebx swtch () at swtch.s:16 16 pushl %esi swtch () at swtch.s:17 17 pushl %edi swtch () at swtch.s:20 20 movl %esp, (%eax) 21 movl %edx, %esp swtch () at swtch.s:24 24 popl %edi swtch () at swtch.s:25 25 popl %esi swtch () at swtch.s:26 26 popl %ebx swtch () at swtch.s:27 27 popl %ebp swtch () at swtch.s:28 28 ret forkret () at proc.c: { forkret () at proc.c: release(&ptable.lock); release (lk=<error reading variable: can't compute CFA for this frame>, lk@entry=0x80112da0 <ptable>) at spinlock.c:48 48 { 49 if(!holding(lk)) holding (lock=0x80112da0 <ptable>) at spinlock.c:92 92 return lock->locked && lock->cpu == cpu; release (lk=<error reading variable: can't compute CFA for this frame>, lk@entry=0x80112da0 <ptable>) at spinlock.c:52 52 lk->pcs[0] = 0; 53 lk->cpu = 0; Breakpoint 1, swtch () at swtch.s:10 10 movl 4(%esp), %eax (gdb) clear

7 Deleted breakpoint 1 (gdb) break exec Breakpoint 2 at 0x801009b0: file exec.c, line 12. [New Thread 2] [Switching to Thread 2] Breakpoint 1, exec (path=0x1c "/init", argv=argv@entry=0x8dfffeb0) at exec.c:12 12 { 21 begin_op(); Ran the following command in the Xv6 main terminal init: starting sh $ ls -l The Breakpoint was hit at the other terminal Breakpoint 1, exec (path=0x1940 "ls", argv=argv@entry=0x8dfbeeb0) at exec.c:12 12 { 21 begin_op(); (gdb) print argv[0] $1 = 0x1940 "ls" (gdb) print argv[1] $2 = 0x1943 "-l" (gdb) print argv[2] $3 = 0x0 Ran Backtrace command (gdb) backtrace #0 exec (path=0x1940 "ls", argv=argv@entry=0x8dfbeeb0) at exec.c:21 #1 0x801051d3 in sys_exec () at sysfile.c:418 #2 0x in syscall () at syscall.c:133 #3 0x801056c1 in trap (tf=0x8dfbefb4) at trap.c:43 #4 0x801054aa in alltraps () at trapasm.s:23 #5 0x8dfbefb4 in?? () Backtrace stopped: previous frame inner to this frame (corrupt stack?) (gdb) up #1 0x801051d3 in sys_exec () at sysfile.c: return exec(path, argv); (gdb) list 413 break; 414 } 415 if(fetchstr(uarg, &argv[i]) < 0) 416 return -1; 417 } 418 return exec(path, argv);

8 419 } int 422 sys_pipe(void) Learning and Observations: Learned how to run Xv6 in debug mode. Ran various commands to debug and to put breakpoints for debugging. Examined context switching by putting breakpoint on swtch using break swtch command. Ran continue and step commands to step through the context switching functions. Learned how to debug input command from the terminal such as ls -l Also learned how to apply patch to the Xv6 file and updating qemu path in Makefile in order to run Xv6 with Qemu. Difficulties encountered I was getting following error while using break exec Breakpoint 2, exec ( path=<error reading variable: can't compute CFA for this frame>, argv=<error reading variable: can't compute CFA for this frame>, argv@entry=0x8dfffeb0) at exec.c:12 Solution: Applied following patch to existing Makefile CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -Wall -MD - ggdb -m32 -Werror -fno-omit-frame-pointer -gdwarf-2 Answer b) Examined and debugged 'wait' function in proc.c wait function does the following Waits for a child process to exit and return its pid Return -1 if this process has no children. Applied breakpoints in proc.c (gdb) break wait Breakpoint 7 at 0x80103d90: file proc.c, line 232. Execute echo command in the Xv6 main terminal $ echo lab2 It hits the breakpoint at line 7 Breakpoint 7, wait () at proc.c: { Applied more breakpoints in the same wait function (gdb) break 246 Breakpoint 8 at 0x80103e00: file proc.c, line 246. (gdb) break 254

9 Breakpoint 9 at 0x80103e3d: file proc.c, line 254. (gdb) break 262 Breakpoint 10 at 0x80103e52: file proc.c, line 262. (gdb) break 267 Breakpoint 11 at 0x80103deb: file proc.c, line 267. Stepping through the function 236 acquire(&ptable.lock); acquire (lk=lk@entry=0x80114ce0 <tickslock>) at spinlock.c:27 27 pushcli(); // disable interrupts to avoid deadlock. Breakpoint 11, wait () at proc.c: sleep(proc, &ptable.lock); //DOC: wait-sleep It switches to thread 2 and execute echo command in the Xv6 main terminal $ echo lab2 lab2 In the other terminal breakpoint is hit [Switching to Thread 2] Breakpoint 8, wait () at proc.c: pid = p->pid; Breakpoint 9, wait () at proc.c: p->state = UNUSED; 255 release(&ptable.lock); (gdb) next 269 } (gdb) next 256 return pid; Finally wait function returns the pid for the child process. Answer C) Disassemble the kernel in i386 While running in debug mode, following commands were executed (gdb) set disassembly-flavor intel (gdb) disass Dump of assembler code for function acquire: 0x801041b0 <+0>: push ebp

10 0x801041b1 <+1>: mov ebp,esp 0x801041b3 <+3>: sub esp,0x18 0x801041b6 <+6>: pushf 0x801041b7 <+7>: pop ecx 0x801041b8 <+8>: cli 0x801041b9 <+9>: mov eax,gs:0x0 0x801041bf <+15>: mov edx,dword PTR [eax+0xac] 0x801041c5 <+21>: test edx,edx 0x801041c7 <+23>: jne 0x801041d5 <acquire+37> 0x801041c9 <+25>: and ecx,0x200 0x801041cf <+31>: mov DWORD PTR [eax+0xb0],ecx 0x801041d5 <+37>: add edx,0x1 0x801041d8 <+40>: mov DWORD PTR [eax+0xac],edx 0x801041de <+46>: mov edx,dword PTR [ebp+0x8] 0x801041e1 <+49>: mov ecx,dword PTR [edx] 0x801041e3 <+51>: test ecx,ecx 0x801041e5 <+53>: je 0x801041ec <acquire+60> 0x801041e7 <+55>: cmp eax,dword PTR [edx+0x8] 0x801041ea <+58>: je 0x <acquire+120> 0x801041ec <+60>: mov ecx,0x1 0x801041f1 <+65>: jmp 0x801041fb <acquire+75> ---Type <return> to continue, or q <return> to quit---return 0x801041f3 <+67>: nop 0x801041f4 <+68>: lea esi,[esi+eiz*1+0x0] => 0x801041f8 <+72>: mov edx,dword PTR [ebp+0x8] 0x801041fb <+75>: mov eax,ecx 0x801041fd <+77>: lock xchg DWORD PTR [edx],eax 0x <+80>: test eax,eax 0x <+82>: jne 0x801041f8 <acquire+72> 0x <+84>: mfence 0x <+87>: mov eax,dword PTR [ebp+0x8] 0x a <+90>: mov edx,dword PTR gs:0x0 0x <+97>: add eax,0xc 0x <+100>: mov DWORD PTR [eax-0x4],edx 0x <+103>: mov DWORD PTR [esp+0x4],eax 0x b <+107>: lea eax,[ebp+0x8] 0x e <+110>: mov DWORD PTR [esp],eax 0x <+113>: call 0x <getcallerpcs> 0x <+118>: leave 0x <+119>: ret 0x <+120>: mov DWORD PTR [esp],0x x f <+127>: call 0x <panic> Answer d) Implementation of cp command to copy one file to two others /* * copy command, cp for xv6 which copies one file to two other files */ #include "types.h" #include "stat.h" #include "user.h"

11 #include "fcntl.h" char buf[512]; void copy(char *file1, char *file2){ int fd0, fd1, n; // Validation for opening of files if((fd0 = open(file1, O_RDONLY)) < 0){ printf(1, "cp: cannot open %s\n", file1); exit(); } if((fd1 = open(file2, O_CREATE O_RDWR)) < 0){ printf(1, "cp: cannot open %s\n", file2); exit(); } } // Read file1 and write it to file2 while((n = read(fd0, buf, sizeof(buf))) > 0){ write(fd1, buf, n); } close(fd0); close(fd1); int main(int argc, char *argv[]) { // Check for number of parameters if(argc <= 3){ printf(1, "Need 3 arguments!\n"); exit(); } //Call copy function twice to copy from first file to other files copy(argv[1], argv[2]); copy(argv[1], argv[3]); exit(); } Testing and Execution a) Ran ls command. Output shows that cp has been added to Xv6 $ ls README cat echo forktest grep init

12 kill ln ls mkdir rm sh stressfs usertests wc cp zombie console b) Ran cp command with no parameters $ cp Need 3 arguments! c) Ran cp command with only one parameter $ cp README Need 3 arguments! d) Ran cp with valid parameters $ cp README myfile1 myfile2 e) Ran ls command to see whether files have been added. Output show files have been added with exact same size (in bytes) as of README. $ ls README cat echo forktest grep init kill ln ls mkdir rm sh stressfs usertests wc cp zombie console myfile myfile

13 f) Ran cat command for myfile1 and myfile2 to test the content of the files. Output shows that files have been successfully copied from README. $ cat myfile1 xv6 is a re-implementation of Dennis Ritchie's and Ken Thompson's Unix Version 6 (v6). xv6 loosely follows the structure and style of v6, but is implemented for a modern x86-based multiprocessor using ANSI C. ACKNOWLEDGMENTS xv6 is inspired by John Lions's Commentary on UNIX 6th Edition (Peer to Peer Communications; ISBN: ; 1st edition (June 14, 2000)). See also which provides pointers to on-line resources for v6. xv6 borrows code from the following sources: JOS (asm.h, elf.h, mmu.h, bootasm.s, ide.c, console.c, and others) Plan 9 (entryother.s, mp.h, mp.c, lapic.c) FreeBSD (ioapic.c) NetBSD (console.c) The following people have made contributions: Russ Cox (context switching, locking), Cliff Frey (MP), Xiao Yu (MP), Nickolai Zeldovich, and Austin Clements. We are also grateful for the bug reports and patches contributed by Silas Boyd-Wickizer, Cody Cutler, Mike CAT, Nelson Elhage, Nathaniel Filardo, Peter Froehlich, Yakir Goaron, Shivam Handa, Bryan Henry, Jim Huang, Anders Kaseorg, kehao95, Wolfgang Keller, Eddie Kohler, Imbar Marinescu, Yandong Mao, Hitoshi Mitake, Carmi Merimovich, Joel Nider, Greg Price, Ayan Shafqat, Eldar Sehayek, Yongming Shen, Cam Tenny, Rafael Ubal, Warren Toomey, Stephen Tu, Pablo Ventura, Xi Wang, Keiichi Watanabe, Nicolas Wolovick, Jindong Zhang, and Zou Chang Wei. The code in the files that constitute xv6 is Copyright Frans Kaashoek, Robert Morris, and Russ Cox. ERROR REPORTS If you spot errors or have suggestions for improvement, please send to Frans Kaashoek and Robert Morris (kaashoek,rtm@csail.mit.edu). If you have suggestions for improvements, please keep in mind that the main purpose of xv6 is as a teaching operating system for MIT's For example, we are in particular interested in simplifications and clarifications, instead of suggestions for new systems calls, more portability, etc.

14 BUILDING AND RUNNING XV6 To build xv6 on an x86 ELF machine (like Linux or FreeBSD), run "make". On non-x86 or non-elf machines (like OS X, even on x86), you will need to install a cross-compiler gcc suite capable of producing x86 ELF binaries. See Then run "make TOOLPREFIX=i386-jos-elf-". To run xv6, install the QEMU PC simulators. To run in QEMU, run "make qemu". To create a typeset version of the code, run "make xv6.pdf". This requires the "mpage" utility. See $ cat myfile2 xv6 is a re-implementation of Dennis Ritchie's and Ken Thompson's Unix Version 6 (v6). xv6 loosely follows the structure and style of v6, but is implemented for a modern x86-based multiprocessor using ANSI C. ACKNOWLEDGMENTS xv6 is inspired by John Lions's Commentary on UNIX 6th Edition (Peer to Peer Communications; ISBN: ; 1st edition (June 14, 2000)). See also which provides pointers to on-line resources for v6. xv6 borrows code from the following sources: JOS (asm.h, elf.h, mmu.h, bootasm.s, ide.c, console.c, and others) Plan 9 (entryother.s, mp.h, mp.c, lapic.c) FreeBSD (ioapic.c) NetBSD (console.c) The following people have made contributions: Russ Cox (context switching, locking), Cliff Frey (MP), Xiao Yu (MP), Nickolai Zeldovich, and Austin Clements. We are also grateful for the bug reports and patches contributed by Silas Boyd-Wickizer, Cody Cutler, Mike CAT, Nelson Elhage, Nathaniel Filardo, Peter Froehlich, Yakir Goaron, Shivam Handa, Bryan Henry, Jim Huang, Anders Kaseorg, kehao95, Wolfgang Keller, Eddie Kohler, Imbar Marinescu, Yandong Mao, Hitoshi Mitake, Carmi Merimovich, Joel Nider, Greg Price, Ayan Shafqat, Eldar Sehayek, Yongming Shen, Cam Tenny, Rafael Ubal, Warren Toomey, Stephen Tu, Pablo Ventura, Xi Wang, Keiichi Watanabe, Nicolas Wolovick, Jindong Zhang, and Zou Chang Wei. The code in the files that constitute xv6 is Copyright Frans Kaashoek, Robert Morris, and Russ Cox.

15 ERROR REPORTS If you spot errors or have suggestions for improvement, please send to Frans Kaashoek and Robert Morris If you have suggestions for improvements, please keep in mind that the main purpose of xv6 is as a teaching operating system for MIT's For example, we are in particular interested in simplifications and clarifications, instead of suggestions for new systems calls, more portability, etc. BUILDING AND RUNNING XV6 To build xv6 on an x86 ELF machine (like Linux or FreeBSD), run "make". On non-x86 or non-elf machines (like OS X, even on x86), you will need to install a cross-compiler gcc suite capable of producing x86 ELF binaries. See Then run "make TOOLPREFIX=i386-jos-elf-". To run xv6, install the QEMU PC simulators. To run in QEMU, run "make qemu". To create a typeset version of the code, run "make xv6.pdf". This requires the "mpage" utility. See Learnings and Observations: a) Learned various functions for reading/writing files (e.g. read(), open() and write()) b) Learned how to implement a new command in the Xv6. All the required parts for this lab were successfully completed.