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28 Cards in this Set
- Front
- Back
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What are some advantages of high-level Languages? |
-give symbolic names to values -provides abstraction of underlying hardware -provides expressiveness -enhances readability -safeguards against bugs |
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What are two different strategies in translating high-level languages? |
-interpretation -compilation |
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What are advantages to interpretation? |
-easy to debug, make changes -one command per line |
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What are advantages to compilation? |
-translate statements into machine language -harder to debug |
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What are two ways of passing parameters to a function? |
call-by-value - caller passes value to function and function holds copy - caller does not see changes call-by-reference: caller passes address of a variable to the function - caller and function operate on same value |
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What is the header structure for main? |
int main ( int argc, char * argv[] ) argc is no. of arguments including name of program argv[] is listing of all the arguments |
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What is stored in a symbol table? |
stores name, type, location, scope |
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What is R5? |
frame pointer -holds address of the base of current frame stack grows downward so offsets are <= 0 |
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What is R6? |
R6 points to top of stack |
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What is R4? |
global data pointer - grows upwards after instructions - points to base |
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Why are global variables initialized but function variables not? |
static variables are initialized at compile-time, since their address is known and fixed. Initializing them to 0 does not incur a runtime cost. automatic variables can have different addresses for different calls and would have to be initialized at runtime each time the function is called, incurring a runtime cost that may not be needed. If you do need that initialization, then request it. |
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What is an activation record? |
information about each function including arguments, local variables, return address stored on run-time stack |
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What happens in calling a function from the point of view of the caller? |
copy values into arguments call function (after function complete) get result from stack |
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What happens in calling a function from the point of view of the called function? |
set up environment execute code put result in activation record pop activation record from stack return |
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Which register points to the beginning of the activation record's local variable store? |
Frame pointer R5 |
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What happens when a new function is called? |
it's activation record is pushed onto the stack |
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What happens when a function returns? |
its activation record is popped off the stack |
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In the activation record, what comes before the local variables?
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arguments starting from last argument then return value then return address then dynamic link |
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What is a dynamic link? |
-caller's frame pointer -used to pop this activation record from the stck |
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What is the return address? |
pointer to NEXT INSTRUCTION in calling function convenient location to store R7 in case another function is called |
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Is the return value allocated if the function does not return a value? |
YES |
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What does JSR do? |
Jumps to location AND saves current PC (next instruction) in R7 |
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What is linking? |
saving the return address |
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What is determined by bit 11 of JSR? |
if 1 - target address = (PC + Sext(IR[10:0])) if 0 - target address = contents of register IR[8:6] JSRR in book |
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What is the sequence for returning from a function? |
copy return value pop local variables pop dynamic link pop return address |
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What does the RET command do? |
JMP R7 |
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What happens when the caller resumes? |
load return value perform assignment pop return value pop arguments |
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summary of LC-3 function call implementation? |
caller pushes arguments (last to first) caller invokes subroutine with JSR callee allocates return value, pushes R7 & R5 callee allocates space for local variables callee executes function code callee stores results into return value slot callee pops local vars, R5, R7 caller loads return value and pops argument caller resumes computation |
