Is there any reason why the PROLOGUE and EPILOGUE can't be redefined to not create a stack frame. I know stack frames have their uses, but most the time we could just reference from ESP. I think MASM will always use for locals and passed params, then I need to write my own assembler. :) I like the type checking of the PROC, but I think it should manage the stack for us, too. :) Even if I put something on it - as long as it's not in a varible loop, it should know to adjust all the varibles that point to locals on the stack :) A better way exists. bitRAKE
OK, let's clear up a few points. First, PROC does not do any param checking. PROTO and INVOKE together do that, with PROTO telling the compiler how many parameters to expect, and INVOKE providing those parameters. MASM32 does no type checking, so the only thing that may be checked is the count. However, INVOKE does expect to ultimately call a procedure. You can't trick it to INVOKE a lable (more later). Now then, together PROC and ENDP do establish a stack frame. At the top of a procedure a PROC will add this to your code:
The last number subtracted being the count of bytes allocated on the stack for LOCALS. Each time a RET is issued inside a PROC, this code is emitted:
push ebp ; save previous ebp mov ebp, esp ; set ebp for the frame add esp, 0FFFFFFF0h ; -16D for 4 dwords
The "leave" instruction does the inverse to ebp as we did upon entry:
leave ret 000Fh
That's all the PROLOGUE and EPILOGUE do. They can't be redefined to not create a stack frame, because that is their one task in life. MASM is quite optomized, meaning if you don't use the stack frame, it does not generate one. Referencing your variables from esp is fine if you like keeping track of lots of little nit picking details, such as procedure parameters are higher then esp and LOCALS are lower... unless of cource you've pushed anything on the stack, then LOCALS may be lower. No one needs this headache. If you think you know better then the compiler, then go have at it. Nothing says you MUST use PROC and ENDP. Just write your procedure without them. CALL a lable (after pushing the required params), and keep track of where esp is NOW relative to where it was when you last pushed something there. And make sure you pop all the params off the stack at exit. Get this right or you'll crash fast and hard. But if you do this, you'll hate yourself in the morning. ;-)
mov esp, ebp ; restore esp from theframe pop ebp ; restore previous ebp
You can use ESP to refer to parameter and locals. But I hope there is atleast one reason for using EBP than esp. Let me try to explain it. When you are declaring a function/procedure in MASM, it creates the following stuff for you. If you declare a function like this,
function PROC param1:DWORD LOCAL local1:DWORD . . . function ENDP
it generates the code like this: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
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 callerinstruction. 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.
Mov ebp, espsaves the value for you. NOTE: You can achieve the same effect with a single instruction
Push ebpI think it is too slow. See AOA. MASM generates LEAVE instruction. What it does? Its effect is equivalent to
Enter 0, 4It 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
Mov esp, ebp Pop ebp Or Add esp, 4 Pop ebpGood 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.
Sub esp, SIZE_OF_VARIABLE
I was just hoping there was a way to coherse MASM into manange my headaches :P I have done without PROC/INVOKE in other assemblers. Yes, it's helpfull to say the least - I'm not knocking it that hard :) Just saying some stuff could be better, or at least have more options :) Thanks for clearing things up Ernie :) I did mis-understand the 'typing' of stuff - should be counting :) I suppose it documents the code as well. It really wouldn't be a headache if you could define prologue and epilogue yourself in more detail. Just like other macros aren't a headache. Thanks for your help, bitRAKE
Primarily a PROC is a label followed by a RET.
You can do all of this stuff manually but it just does not work any better and it is very error prone code to write. There is no problem in code to use "CALL LABEL" and at times if you have a block of code that you need to call recursively, you can use this technique to some advantage in terms of speed over using a normal procedure. There are some examples in the MASM32 example code under the directory TSTYLE but they are examples of how NOT to write code. Regards, email@example.com
label: ; address of following instruction ; your code RET Assuming STDCALL and DWORD size you call a proc as follows, push par4 push par3 push par2 push par1 call label_address To keep track of the stack in the PROC that is being called, it preserves the base pointer (EBP) and copies the stack pointer into it. push ebp ; preserve base pointer mov ebp, esp ; stack pointer into ebp To access the four parameters pushed onto the stack within the PROC, you start from the address . = par1 = par2 = par3 = par4 At the completion of the code in the PROC you restore the stack pointer(ESP) and the base pointer(EBP). mov esp, ebp ; restore stack pointer pop ebp ; restore base pointer ret This leaves you with a balanced stack and the correct adress so that RET jumps back to the following instruction after CALL. If this is messed up you get EXTREMELY unpredictable results READ ==> (CRASH). :)
Actually, you can make masm not generate epilogue/prologue. Only problem is that locals and paramaters to the PROC will not be accessible automatically, and you will have to do manual ESP referencing. As far as I remember, epilogue and prologue can be set to use any macro you desire - with "none" being the only one I can think of a use for. As for opcodes being one byte larger when using ESP...I have only one thing to say: sometimes an extra free register (EBP) is much more worth than a small(!) increase in opcode size. And, yes, removing prologue/epilogue can be very useful. Jump tables. Then again, you could just use labels for that.