assembly
types of assembly:
Programmers model for MIPS
32 bit (4 byte) registers (1 word)
add $r7, $r4, $r3 | r7 = r4 + r3
dollar sign implies it is a variable, no dollar sign is a constant
special registers: program counter, stack pointer (points to end of stack frame)
memory is laid out in words as well
assembly: address, immediate C : pointer, constant
types of registers:
- $r0: always 0
- $at: assembler temporary, for expanding macros
- $v0, $v1: return
- $ra where to return to
- \(ao-\)a3, 4 args. Any more need to be on the stack
- \(s0-\)s7, \(t0-\)t9 local variables
registers are the only variables you can access directly
Load and Store
to get to the RAM
assembler takes symbols and makes a symbol table mapping symbols to addresses
array[index] is backwards in assembly, assembly has x($t1) which is t1[x / word size]
.word lets you define a symbol .space allows you to ask for space
call frame is an array off the stack pointer
jump to address,
beq lets you branch conditionally
jal: jump and link, jumps and sets the $ra for you to pc+word
calling multiple functions, you have to store the old $ra value to prevent $ra from getting overwritten by a jal
caller saved registers can be overwritten after a call, so if you’re making a call, it’s your responsibility to save them if you need them later.
callee saved registers are expected to be the same after a return, so if you want to change them, you better restore them before you exit
MARS assembly simulator
