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4.1 Runtime Administration

The document provides an overview of runtime memory organization in computer science, detailing the different types of memory allocation strategies: static, stack, and heap. It explains the structure of activation records and how they manage memory for procedures, including access to non-local variables. The document emphasizes the trade-offs between efficiency and flexibility in memory allocation methods.

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17 views11 pages

4.1 Runtime Administration

The document provides an overview of runtime memory organization in computer science, detailing the different types of memory allocation strategies: static, stack, and heap. It explains the structure of activation records and how they manage memory for procedures, including access to non-local variables. The document emphasizes the trade-offs between efficiency and flexibility in memory allocation methods.

Uploaded by

nikhil.2226cse1108
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Computer Science and Engineering

Anubhav Patrick

Assistant Professor
Fifth
Compiler Design
KCS502
Runtime Administration

A quick tutorial on Lex 1


Runtime Environment
l Run time memory organization.
char abc[1000];
char *fun1() { char buf[50], *c; buf[0] = ‘\0’; c=malloc(50);
return( c );}
main() {char *c; c = fun1();}

} We need to use memory to store:


– Code
– Static data (global variables)
– Dynamic data objects
• Data that are used when executing a certain procedure.
• Dynamically allocated objects (malloc, free).
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Typical organization of run-time memory

Low Address
Code

Static Data (global variables)

Stack (memory for procedures)

Heap (memory for dynamically allocated data)


High Address

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Activation Records
l Also called frames
l Information (memory) needed by a single execution of a procedure
l A general activation record:
return value
actual parameters
optional control link
optional access link
machine status
local variables
temporaries
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Types of Allocation
l Storage Allocation Strategies
} Static Allocation lays out storage for all data objects at compile time.
– Restrictions:
• Size of object must be known and alignment requirements must be known at compile time.
• No recursion.
• No dynamic data structure
} Stack allocation manages the run time storage as a stack
– The activation record is pushed on a stack as a function is entered.
– The activation record is popped off a stack as a function exits.
– Restrictions:
• Values of locals cannot be retained when an activation ends.
• A called activation cannot outlive a caller.

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Types of Allocation
} Heap allocation allocates and deallocates storage as needed at runtime
from a data area known as heap.
– Advantage:
• Most flexible: no longer requires the activation of procedures to be LIFO.
– Disadvantage:
• Most inefficient: need true dynamic memory management.

l Note: static allocation too restricted, heap allocation too inefficient. Most
current compiler/language/processor uses the stack allocation scheme.

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Example of stack allocation (downward
growing):

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Access to Non-Local Variables
l Access to nonlocal variables.
} e.g., Nonlocal variables in PASCAL (with nested procedures):
} The scheme for C will break (static for all non-locals).
} Solution -> Access links
– If p is nested immediately within q in the source text, then the access link in an
activation record for p points to the access link in the record for the most recent
activation of q.
– If a procedure p at nesting depth np accesses a nonlocal variable x which is an
element defined within some procedure q that surrounds p and has nesting depth nq:
we follow access links np – nq times

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Access to Non-Local Variables

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Access Links

10
Thank You

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