Introduction to Computer Systems Homework 2

cs154: Introduction to Computer Systems

Homework 2

Submit your answers by adding and committing one file with your answers into the hw2 directory of your
CNETID-cs154-spr-20 svn repository1
. The file should be named either hw2.txt or hw2.pdf for
answers written in a plain ASCII text file or PDF file, respectively. PDFs of scanned hand-written pages must
not exceed 5 megabytes. No other file formats or filenames are acceptable, and no files besides hw2.txt
or hw2.pdf will be graded. Not following directions may result in losing points.
Note: Some of the operands and instructions below use the scaled indexed addressing mode. As the caption
for Figure 3.3 in the book explains, for x86 the valid scaling factors are 1, 2, 4, or 8. For this homework and
this homework only, however, you should assume that there are no restrictions on scaling factors.
(Q1. 12 points + 2 bonus points) The following values are stored at the indicated memory
addresses and registers:
Address Value Register Value
0x210 0xAB %rax 0x210
0x218 0xBC %rcx 0x220
0x220 0x09 %rdx 0x1
0x228 0x42 %rsi 0x8
0x230 0x54 %rdi 0x100
Assume that the Values occupy eight bytes of storage, but the endianness of storage is not specified. Each
part of this question concerns one item in the following list of operands. For the operands, give the Value of
the operand, and the addressing Mode used (copying from the “Name” column of Figure 3.3 in the textbook).
If the facts given here don’t provide sufficient information to answer the question unambiguously, for Value
say “unknown”, and for Mode give an explanation of what information is missing, without which there isn’t
an unambiguous answer. Give all Values in hex (unsigned), starting with “0x”.
Part Operand Value Mode
e.g. %rax 0x210 Register
A. (%rcx)
B. 560
C. (%rax,%rsi)
D. 0x108(%rdi,%rdx,0x20)
E. $251
F. (,%rsi,0x45)
(Bonus) G. 0x14(%rax)
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see https://classes.cs.uchicago.edu/current/15400-1/svn.html
(Q2. 20 points) Assume the same information about addresses, registers, and values as in the previous
question. The table is reprinted here for convenience:
Address Value Register Value
0x210 0xAB %rax 0x210
0x218 0xBC %rcx 0x220
0x220 0x09 %rdx 0x1
0x228 0x42 %rsi 0x8
0x230 0x54 %rdi 0x100
Each part of this question concerns a single instruction. Each instruction is to be considered in isolation (the
answer for one instruction does not affect any other instruction). The argument ordering for the instructions
is the same ATT format (not Intel format) as used in the book. Negative values are represented with two’s
complement.
For each part, give the Destination for the instruction (as either “0xADDR” for address ADDR or as ‘%reg”
for register reg), and the (unsigned) Value (in hex, starting with “0x”) stored in the Destination. If the
facts given don’t provide sufficient information to answer the question unambiguously, give “unknown” for
Destination, and a terse explanation why for Value.
Part Instruction Destination Value
e.g. addq %rdx,(%rax) 0x210 0xAC
A. incq %rsi
B. decq (%rax)
C. notq %rdx
D. shlq %rsi,(%rcx)
E. subq $0x100,%rcx
F. imulq %rdi,(%rax,%rsi)
G. orq (%rcx),%rax
H. shrq %rdx,(%rdi,%rsi,37)
I. xorq %rbx,%rbx
J. subq 0x220,%rdi
Note: For this homework, it is fine to use a calculator or some other program to aid with arithmetic.
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