Memory Layout and Stack Frame Allocation in SPIM, Study notes of Computer Science

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SPIM Memory Layout

Stack Segment Data SegmentText Segment

0x7fffff^ 0x

Layout of Memory

Layout of a Stack Frame

Parameter 5Parameter 6Parameter 7

... Saved RegistersLocal Variables Dynamic Variables

$fp $sp

Calling a Procedure: •^ Execute a

jal

instruction.

At the beginning of the called Procedure: •^ Register

$ra

needs to be saved to the location referenced by the stack

pointer • The appropriate display register must be saved into the following word ofthe stack frame. Save any other callee-saved registers in the frame. • Establish the new display pointer by copying

$sp

into the appropriate

display register. • Establish the stack frame by subtracting the frame size from the stackpointer. To return from a call: • Pop the stack frame by adding the frame size to

$sp

-^ Restore callee-saved registers, including the appropriate display register. •^ Return by jumping to the address in register

$ra

(it is also at the location

now referenced by

$sp

Procedures: No Parameters, with Recursion

Calling a Procedure: •^ Pass the parameters. By convention, the first four parameters are passed inregisters

$a0-$a

. The remaining arguments are pushed on the stack -^ Set up the static chain register (necessary if the procedure is nested withinanother dynamically allocated scope). •^ Save the caller-saved registers,

$t0-$t

, if they contain live values at the call

site. • Execute a

jal

instruction.

At the beginning of the called Procedure: •^ Save the callee-saved registers in the frame. Register

$fp

must be saved

since it is being used to reference variables in the calling frame. Register $ra

needs to be saved in order to allow the routine itself to make calls. Any of the registers

$s0-$s

that are used by the callee need to be saved.

-^ Establish the stack frame by subtracting the frame size from the stackpointer. Establish the frame pointer

$fp

by adding the stack frame size to

$sp

Procedures: Parameters and Recursion with Chains