Architecture 04

Question 1

What is the general form of memory addressing word in the x86 architecture?

Answer 1

disp (%reg1, %reg2, scale)
• disp is a constant integer (offset)
• reg1 is the base register of the operand
• reg2 is the index register of the operand
• scale can only be 1, 2, 4, 8

Question 2

Show how you could use indirect mode addressing in the x86 architecutre

Answer 2

General: disp (%reg1, %reg2, scale)

Indirect mode: (%reg1)

Question 3

Show how you could use direct mode addressing in the x86 architecutre

Answer 3

General: disp (%reg1, %reg2, scale)

Direct mode: disp

Question 4

What is meant by AT&T syntax?

Answer 4

A convention for assembly languages, for example in AT&T syntax the destination address comes last:
• movq source, dest

Question 5

What is the typical characteristic of a CISC instruction?

Answer 5

The instruction combines load of values and the arithmetic

Question 6

What is meant by assembly calling convention?

Answer 6

A convention people agree on for assembly languages, declaring
• How arguments are passed
• How results are returned
• How registers may be used for storing intermediate values

Question 7

What is the calling convention for C on x86-64 in terms of function arguments?

Answer 7

If
• A Function has N <= 6 arguments
• And all fit into 64 bits

Then the arguments are stored in the first N of
rdi rsi rdx rcx r8 r9

Additional (and longer than 64 bit) arguments go on the stack

Question 8

What is the calling convention for C on x86-64 in terms of return value?

Answer 8

If return type fits in 64 fits, then it is returned in rax

Question 9

What are the characteristics of a high level language?

Answer 9

• One to many translation (each statement corresponds to multiple machine level instructions)
• Hardware independence (Abstracts over underlying hardware)
• Application orientation (Designed to create application programs)
• General purpose (Not restricted to a specific task)
• Powerful abstractions (Complex tasks can be expressed succinctly)

Question 10

What are the characteristics of a low level language?

Answer 10

• One to one translation (each statement correspons to one machine level instruction)
• Hardware dependence (Dependent on type of processor)
• Systems programming orientation (Can create software that directly controls hardware)
• Special purpose (Used when extreme control or efficiency is needed)
• Few abstractions (Forces programmer to construct abstractions)