2 Jan
2009
2 Jan
'09
8:25 a.m.
Since SP is in I/O space and not register space, it
takes extra
instructions to perform stack-relative addressing (got to get SP into
X, Y, or Z) for stack-local variables, etc.
Nothing says that the hardware's stack has to be the same as the C
local-variable stack, and indeed on an architecture like that it might
be smarter to use the hardware's stack - the thing SP points to - only
for return addresses, with local variables and arguments kept on a
separate stack, maintained by the function call/return boilerplate.
Of course, that means you have to keep the data stack pointer
somewhere, since you can't keep it in SP for free....
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