From 01a6c054d548d9fff8bbdfac4d3f3de4ae8677a1 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Wed, 7 Sep 2011 11:49:14 -0400 Subject: Remove web directory; all cruft or moved to 6.828 repo --- web/xv6-intro.html | 163 ----------------------------------------------------- 1 file changed, 163 deletions(-) delete mode 100644 web/xv6-intro.html (limited to 'web/xv6-intro.html') diff --git a/web/xv6-intro.html b/web/xv6-intro.html deleted file mode 100644 index 3669866..0000000 --- a/web/xv6-intro.html +++ /dev/null @@ -1,163 +0,0 @@ -Homework: intro to xv6 - - - - - -

Homework: intro to xv6

- -

This lecture is the introduction to xv6, our re-implementation of - Unix v6. Read the source code in the assigned files. You won't have - to understand the details yet; we will focus on how the first - user-level process comes into existence after the computer is turned - on. -

- -Hand-In Procedure -

-You are to turn in this homework during lecture. Please -write up your answers to the exercises below and hand them in to a -6.828 staff member at the beginning of lecture. -

- -

Assignment: -
-Fetch and un-tar the xv6 source: - -

-sh-3.00$ wget http://pdos.csail.mit.edu/6.828/2007/src/xv6-rev1.tar.gz 
-sh-3.00$ tar xzvf xv6-rev1.tar.gz
-xv6/
-xv6/asm.h
-xv6/bio.c
-xv6/bootasm.S
-xv6/bootmain.c
-...
-$
-

- -Build xv6: -

-$ cd xv6
-$ make
-gcc -O -nostdinc -I. -c bootmain.c
-gcc -nostdinc -I. -c bootasm.S
-ld -N -e start -Ttext 0x7C00 -o bootblock.o bootasm.o bootmain.o
-objdump -S bootblock.o > bootblock.asm
-objcopy -S -O binary bootblock.o bootblock
-...
-$ 
-

- -Find the address of the main function by -looking in kernel.asm: -

-% grep main kernel.asm
-...
-00102454 <mpmain>:
-mpmain(void)
-001024d0 <main>:
-  10250d:       79 f1                   jns    102500 <main+0x30>
-  1025f3:       76 6f                   jbe    102664 <main+0x194>
-  102611:       74 2f                   je     102642 <main+0x172>
-

-In this case, the address is 001024d0. -

- -Run the kernel inside Bochs, setting a breakpoint -at the beginning of main (i.e., the address -you just found). -

-$ make bochs
-if [ ! -e .bochsrc ]; then ln -s dot-bochsrc .bochsrc; fi
-bochs -q
-========================================================================
-                       Bochs x86 Emulator 2.2.6
-                    (6.828 distribution release 1)
-========================================================================
-00000000000i[     ] reading configuration from .bochsrc
-00000000000i[     ] installing x module as the Bochs GUI
-00000000000i[     ] Warning: no rc file specified.
-00000000000i[     ] using log file bochsout.txt
-Next at t=0
-(0) [0xfffffff0] f000:fff0 (unk. ctxt): jmp far f000:e05b         ; ea5be000f0
-(1) [0xfffffff0] f000:fff0 (unk. ctxt): jmp far f000:e05b         ; ea5be000f0
-<bochs> 
-

- -Look at the registers and the stack contents: - -

-<bochs> info reg
-...
-<bochs> print-stack
-...
-<bochs>
-

- -Which part of the stack printout is actually the stack? -(Hint: not all of it.) Identify all the non-zero values -on the stack.

- -Turn in: the output of print-stack with -the valid part of the stack marked. Write a short (3-5 word) -comment next to each non-zero value explaining what it is. -

- -Now look at kernel.asm for the instructions in main that read: -

-  10251e:       8b 15 00 78 10 00       mov    0x107800,%edx
-  102524:       8d 04 92                lea    (%edx,%edx,4),%eax
-  102527:       8d 04 42                lea    (%edx,%eax,2),%eax
-  10252a:       c1 e0 04                shl    $0x4,%eax
-  10252d:       01 d0                   add    %edx,%eax
-  10252f:       8d 04 85 1c ad 10 00    lea    0x10ad1c(,%eax,4),%eax
-  102536:       89 c4                   mov    %eax,%esp
-

-(The addresses and constants might be different on your system, -and the compiler might use imul instead of the lea,lea,shl,add,lea sequence. -Look for the move into %esp). -

- -Which lines in main.c do these instructions correspond to? -

- -Set a breakpoint at the first of those instructions -and let the program run until the breakpoint: -

-<bochs> vb 0x8:0x10251e
-<bochs> s
-...
-<bochs> c
-(0) Breakpoint 2, 0x0010251e (0x0008:0x0010251e)
-Next at t=1157430
-(0) [0x0010251e] 0008:0x0010251e (unk. ctxt): mov edx, dword ptr ds:0x107800 ; 8b1500781000
-(1) [0xfffffff0] f000:fff0 (unk. ctxt): jmp far f000:e05b         ; ea5be000f0
-<bochs> 
-

-(The first s command is necessary -to single-step past the breakpoint at main, otherwise c -will not make any progress.) -

- -Inspect the registers and stack again -(info reg and print-stack). -Then step past those seven instructions -(s 7) -and inspect them again. -Convince yourself that the stack has changed correctly. -

- -Turn in: answers to the following questions. -Look at the assembly for the call to -lapic_init that occurs after the -the stack switch. Where does the -bcpu argument come from? -What would have happened if main -stored bcpu -on the stack before those four assembly instructions? -Would the code still work? Why or why not? -

- - - -- cgit v1.2.3