ASM Community

function	PROC	param1:DWORD

	LOCAL	local1:DWORD
	.
	.
	.
function	ENDP



it generates the code like this:


 
function:

	Push	ebp		; Save base pointer
	Mov	ebp, esp	; Point base pointer to stack pointer
	Add	esp, -4		; Allocate space in stack for local
				; Here I find using sub esp, 4 does no
				; harm. But I don't know why MASM does this.
				; I checked the bytes and cycles used
				; for both of them.


	Leave			; Reset base pointer and stack pointer
	Ret	4		; Return to caller


Now the parameter is referred as  and the local as .

1. Why should we use ebp instead of esp?

It generates smaller code when you use ebp than esp.
You save one byte always and no time difference in execution. 
For example, if you refer parametersand locals using EBP, 
say 10 times, you are saving 10 bytes. So all available compilers 
and MASM generates this type of code.

2. Your quote "I like the type checking of the PROC, but I think 
it should manage the stack for us, too."

MASM does that for you. Don't confuse with ebp and esp registers. You see



	Mov	ebp, esp



instruction. Now ebp points to esp. This is required to save bytes. In order
to use ebp at will, you have to save and restore its value.



	Push	ebp



saves the value for you.

NOTE:
	You can achieve the same effect with a single instruction



	Enter	0, 4



I think it is too slow. See AOA.


MASM generates LEAVE instruction. What it does?

	Its effect is equivalent to



	Mov	esp, ebp
	Pop	ebp

Or

	Add	esp, 4
	Pop	ebp



It costs 3 bytes and 6 cycles whereas LEAVE costs 1 byte and 4 cycles.

Also if you don't want to create a stack frame, then pass the
parameter values in available register. That is faster too.

You can allocate space for local at will by



	Sub	esp, SIZE_OF_VARIABLE



Good example will be M32LIB\FPTOA.ASM.

See function FloatToBCD, you see "sub esp, 10" at the start and "add esp, 10"
at the end of the function.