c - Stack / base pointers in assembly -

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i know topic has been covered ad nauseam here, , other places on internet - question simple 1 try head around assembly...

so if understand correctly ebp (base pointer) point top of stack, , esp (stack pointer) point bottom -- since stack grows downward. esp therefore points 'current location'. on function call, once you've saved ebp on stack insert new stack frame - function. in case of image below, if started n-3 go n-2 function call. when @ n-2 - ebp == 25 , esp == 24 (at least initially, before data placed on stack)?

is correct or off on tangent here?

thanks!

http://upload.wikimedia.org/wikipedia/en/a/a7/programcallstack2.png http://upload.wikimedia.org/wikipedia/en/a/a7/programcallstack2.png

this depends upon not hardware architecture , compiler, calling convention, agreed-upon way in functions work stack call 1 another. in other words, there different orders in function can push things onto stack, depending on compiler settings (and peculiar #pragma options, etc, etc).

it looks talking cdecl calling convention on x86 architecture. in case, caller's ebp pushed onto stack after return address. so, in example's n-2, location 25 contain pointer calling function n-3 (ie, contain address of instruction after call got n-2) , location 24 contain old ebp, , esp = 23 after call, before locals have been pushed onto stack. (except compilers make space on stack after call, , esp 20 instead of moving , down inside function n-2.)

however aware on x86 there particular optimization compiler can called frame pointer omission, avoids pushing old ebp onto stack altogether under conditions.


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