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frame pointers and stack pointers
Posted by Nobody/Anonymous on June 24, 2005
Can anyone tell me the difference between frame pointers and stack pointers??
thanks in advance
thanks in advance
RE: frame pointers and stack pointers
Posted by Nobody/Anonymous on June 24, 2005
As an example, assume you are running an 8bit system and you call a function that declares four 8 bit local variables. Also assume your target processor has a stack pointer (SP) and another register X.
A compiler that uses frame pointers (not all do) might behave as follows:
When the function is entered the first thing that is done is to set X equal to SP. Next SP is decremented by 4 (assumes stack grows down). The space between X and SP is used for the four local variables.
Now X is the function frame pointer. It is used to access the four local variables as X+1, X+2, X+3 and X+4.
SP is the stack pointer (obviously still). The function is free to use the stack. If the function allocates more data on the stack then SP will change but X will remain the same - so the four variables can still be access as offsets from X no matter what value SP holds.
A compiler that uses frame pointers (not all do) might behave as follows:
When the function is entered the first thing that is done is to set X equal to SP. Next SP is decremented by 4 (assumes stack grows down). The space between X and SP is used for the four local variables.
Now X is the function frame pointer. It is used to access the four local variables as X+1, X+2, X+3 and X+4.
SP is the stack pointer (obviously still). The function is free to use the stack. If the function allocates more data on the stack then SP will change but X will remain the same - so the four variables can still be access as offsets from X no matter what value SP holds.
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Any and all data, files, source code, html content and documentation included in the FreeRTOSTM distribution or available on this site are the exclusive property of Real Time Engineers Ltd.. See the files license.txt (included in the distribution) and this copyright notice for more information. FreeRTOSTM and FreeRTOS.orgTM are trade marks of Real Time Engineers Ltd.