Implement Subprograms

Question 1

Subroutine linkage

Answer 1

Subroutine call and return operations

Question 2

Implementation of subroutines must be based on ….

Answer 2

Semantics of the subroutine linkage

Question 3

Semantics of a subroutine call (4)

Answer 3

(1) save the execution status of the current Program unit
(2) pass the Parameters
(3) pass the return address to the callee
(4) transfer control to the callee

Question 4

Subroutine return:

If there are pass-by-value-result or out-mode parameters, the current values of those parameters are move to …

Answer 4

The corresponding actual parameters

Question 5

Subroutine return:

Move the return value to…

Answer 5

A place accessible to the caller

Question 6

Subroutine return:

Execution status of the caller is …

Answer 6

Returned

Question 7

Subroutine return:

Control is transferred …

Answer 7

Back to the caller

Question 8

Storage:

Call and return actions require storage for … (5)

Answer 8

Status information about the caller, parameters, return address, return value for functions, and local variables

Question 9

“Simple” subroutines are

Answer 9

Those that cannot be nested and all local variables are static.

Question 10

A simple subroutine consists of two parts: (give def for each to/size)

Answer 10

Code and data
Code: constant (instruction space)
Data: can change when the subroutine is executed (data space)
Both have fixed size

Question 11

Activation record is

Answer 11

The format or layout of the data part because the data is relevant to an activation, execution, of the subroutine

Question 12

The formation of an activation record is

Answer 12

Static

Question 13

An activation record instance is a

Answer 13

Concrete example of an activation record corresponding to one execution

Question 14

An activation record for a simple subroutine

What does the stack look like, size, allocation type, side note

Answer 14

Local var
Params
Return Add

Fixed size (statically allocated)

Could be attached to the code part of the sub Program

Question 15

When each programming unit is compiling is it

Answer 15

Machine code along with a list of references to external sub programs are written to a file

Question 16

A linker is called for …

Answer 16

MAIN to create an executable program

Question 17

What does a linker do? (4)

Answer 17

Is a part of the OS
Also called loader, linker/loader, loader, link editor
Finds and loads all referenced subroutines including code and activation records into memory
Sets the target addresses of calls to those subroutines entry addresses

Question 18

Call stack is

Answer 18

A stack data structure that stores information about the active subroutines of a Program

Also known as execution stack, control stack, runtime stack, machine stack.

Frowns downward in memory towards lower addresses and shrinks upwards

Question 19

The activation record on stack is also called

Answer 19

Stack frame

Question 20

stack pointer (sp) points to

Answer 20

The frame top

Question 21

Frame pointer (to) points

Answer 21

To the frame base

Question 22

Important advantage of stack dynamic local variables

Answer 22

Support for recursion

Question 23

Comple activation record stack contents

Answer 23

Local variables 
Parameters 
Dynamic link 
Return address 
Stacktop

Question 24

Dynamic link (control links) =

Answer 24

Previous sp

Question 25

What is dynamic link used for?

Answer 25

In destruction of the current activation record instance when the procedure completes its execution

Question 26

What does the dynamic link restore?

Answer 26

The sp in the previous frame (caller)

Question 27

What is a collection of dynamic links in the stack at a given time called? And what do the represent?

Answer 27

Called dynamic chain (call chain)

Represents the dynamic history of how execution got to its current position

Question 28

What is the purpose of a dynamic link?

Answer 28

Required when there are allocations from the stack by a subroutine by one it’s activation record (temporaries)
Access biblical variables in dynamic scoped languages

Question 29

Local scalar variables are bound to

Answer 29

Storage within an activation record instance

Question 30

Local variables that are structures are sometimes allocate elsewhere and only leave their …

Answer 30

Descriptors and a pointer to the storage as a part of their activation record

Question 31

Recursion adds the possibility of multiple …

Answer 31

Simultaneous activations of a subroutine at a given time with atleast one call from outside the subroutine and one or more recursive calls.

Question 32

Each recursion activation requires

Answer 32

It’s own activation record instance

Question 33

What static scoped languages use stack dynamic local variables and allow subroutine to be nested?

Answer 33

Fortran, ada, Python, JavaScript

Question 34

Finding access to non local variables in nested subroutines of static scoped Lang but stack dynamic local variables

Answer 34

(1) find activation record instance on the stack where variable is allocation
(2) local-offset of the variables to access it

Question 35

Local offset describes the …

Answer 35

Offset from the beginning/bottom of an activation record

Question 36

Finding activation record instance:

Static chaining (3)

Answer 36

(1) new ptr (static link aka static scope pointer/access links) point to bottom of activation record instance of the static parent
(2) used to access non local varicela
(3) static link appears below parameters on activation record

Question 37

Activation record instance with static link stack

Answer 37

Local variables 
Parameters 
Dynamic link 
Static link 
Return address

Question 38

A static chain is a chain of

Answer 38

Static links that connect the activation record instances of all static ancestors for an executing subroutine

Question 39

Static chain can be used to implement

Answer 39

No local variable access

Question 40

Static_depth and nesting_depth difference

Answer 40

Static depth: how deeply it is nested in the outermost scope for a non local reference

Static depth of a variable definition is the nesting_depth/chain_depth of the reference