X86 calling conventions

x86
Main article: x86 calling conventions
The x86 architecture features many different calling conventions. Due to the small number of architectural registers, the x86 calling conventions mostly pass arguments on the stack, while the return value (or a pointer to it) is passed in a register. Some conventions use registers for the first few parameters, which may improve performance for some very frequently invoked short and simple subroutines.
Example call:
push eAX ; pass some register result
push byte[eBP+20] ; pass some memory variable (FASM/TASM syntax)
push 3 ; pass some constant
call calc ; the returned result is now in eAX
Typical callee structure: (some or all (except ret) of the instructions below may be optimized away in simple procedures)
calc:
push eBP ; save old frame pointer
mov eBP,eSP ; get new frame pointer
sub eSP,localsize ; reserve place for locals
.
. ; perform calculations, leave result in AX
.
mov eSP,eBP ; free space for locals
pop eBP ; restore old frame pointer
ret paramsize ; free parameter space and return
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