1. What is the definition used in this chapter for “simple” subprograms?
Subprograms cannot be nested and all local variables are static.

2. Which of the caller of callee saves execution status information?
Either can save the execution status

3. What must be stored for the linkage to a subprogram?
Execution status information

4. What is the task of a linker?
Find files that contain the translated subprograms referenced in that program and load them into memory, set target addresses of all calls to those subprograms in the main program to the entry addresses of those subprograms.

8. What kind of machines often use registers to pass parameters?
RISC Machines

10. Define static chain, static_depth, nesting_depth,and chain_offset.
– static chain : a chain of static links that connect certain activation record instances in the stack.
– static depth : integer associated with a static scope that indicates how deeply it is nested in the outermost scope.
– nesting_depth : difference between static_depth of a subprogram containing reference to x and the static_depth of a subprogram containing the declaration of x.
– chain_offset : number of links to the correct activation record instance

12. How are references to variables represented in the static-chain method?
It is represented by static depth.

Problem Set

6. Although local variables in Java methods are dynamically allocated at the beginning of each activation, under what circumstances could the value of a local variable in a particular activation retain the value of previous activation?
If the variable is declared as static. Static modifier is a modifier that makes a variable history – sensitive.

7. It is stated in this chapter that when nonlocal variables are accessed in a dynamic-scoped language using the dynamic chain, variable names must be stored in the activation records with the values. If this were actually done, every nonlocal access would require a sequence of costly string comparisons on names. Design an alternative to these string comparisons that would be faster.

Using approach that uses an auxiliary data structure called a display. Or, to write variable names as integers. These integers act like an array. So when the activation happens, the comparisons will be faster.

8. Pascal allows gotos with nonlocal targets. How could such statements be handled if static chains were used for nonlocal variable access? Hint:Consider the way the correct activation record instance of the static parent of a newly enacted procedure is found(see Section 10.4.2).

Based on the hint statement, the target of every goto in a program could be represented as an address and a nesting_depth, where the nesting_depth is the difference between the nesting level of the procedure that contains the goto and that of the procedure containing the target. Then, when a goto is executed, the static chain is followed by the number of links indicated in the nesting_depth of the goto target. The stack top pointer is reset to the top of the activation record at the end of the chain.

9. The static-chain method could be expanded slightly by using two static links in each activation record instance where the second points to the static grandparent activation record instance. How would this approach affect the time required for subprogram linkage and nonlocal references?

Including two static links would reduce the access time to nonlocals that are defined in scopes two steps away to be equal to that for nonlocals that are one step away. Overall, because most nonlocal references are relatively close, this could significantly increase the execution efficiency of many programs.

11. If a compiler uses the static chain approach to implementing blocks, which of the entries in the activation records for subprograms are needed in the activation records for blocks?

There are two options for implementing blocks as parameterless subprograms: One way is to use the same activation record as a subprogram that has no parameters. This is the most simple way, because accesses to block variables will be exactly like accesses to local variables. Of course, the space for the static and dynamic links and the return address will be wasted. The alternative is to leave out the static and dynamic links and the return address, which saves space but makes accesses to block variables different from subprogram locals.