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Subject: Re: GNAT parameter passing, C-style?
Date: Thu, 1 Jan 2004 11:32:45 -0500
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Date: 2004-01-01T11:32:45-05:00
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"Hyman Rosen" <hyrosen@mail.com> wrote in message
news:bAXIb.28439$tY5.3073@nwrdny01.gnilink.net...
> Even if parameters are passed on the stack, there is no need
> to process the arguments from right to left. You can just
> subtract the appropriate amount from the stack pointer and
> then fill in that space by processing the arguments from left
> to right.

The problem, again, is with variable argument lists. For functions with
variable argument lists, such as like printf and fprintf , the "appropriate
amount" will vary from call to call. In any such function, there are one or
more fixed parameters, from which one can the number and type of the
remaining parameters. Before we can determine the size of the argument
block, we must be able to retrieve the first few arguments. Given the "Last
in, First out" nature of a stack, the easiest way to do that is to push the
parameters on the stack in reverse order. With printf, for example, the
format string is the last parameter pushed on the stack. Within printf, the
format string is at the top of the stack, and it can be used to determine
the rest of the parameters.