From mboxrd@z Thu Jan  1 00:00:00 1970
Message-Id: <200207191819.TAA08286@cthulhu.dircon.co.uk>
Subject: Re: [9fans] useful language extension, or no?
In-Reply-To: <ea94bd2f40b35a968b743ea92d20d3d9@vitanuova.com> from "forsyth@vitanuova.com"
 at "Jul 19, 2002 04:45:14 pm"
To: 9fans@cse.psu.edu
From: Digby Tarvin <digbyt@acm.org>
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Date: Fri, 19 Jul 2002 19:19:43 +0100
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Thanks - I guess that confirms it does what I thought.

Are there any good papers on this sort of stuff, or does one
just have to wade through the source code?

Any recomendations on a worthy successor to the K&R book as a
good reference on the current state of the art of the language...?

Regards,
DigbyT

> it only uses the trampoline code when you call g indirectly through
> a function pointer.  if you call it directly it can provide the static link
> itself without that fuss.   when you create a function pointer to g,
> as in the call to printf, it does generate code onto the stack that
> loads the static link register then enters g.
> 	leal -16(%ebp),%eax
> 	movl $g.9-10,%edx
> 	movb $185,(%eax)
> 	movl %ebp,1(%eax)
> 	movb $233,5(%eax)
> 	subl %eax,%edx
> 	movl %edx,6(%eax)
> that's the generation on the fly of the trampoline code.
> note the movl %ebp,1(%eax), which stores the current frame pointer
> as a literal in the generated code.
> the `function pointer' that is later passed to printf is the address of
> -16(%ebp) [offsets might be different in your case], which when
> called will load the literal, and enter g with a pc-relative reference
> (i think that's about right).
> 
> you'd need to flush the cache(s) on some architectures, which is
> tricky when it's a privileged operation.
> 
> the problem it is trying to solve is to get the right value for the static link register,
> without passing the required value along with the function pointer as a pair.
> providing the right value for the static link register is
> easiest to do if it doesn't exist.  there are several
> approaches to implementing displays, and one of them allows nested
> function pointers as a single word but without this crud.
> 
> all these implementations of nested functions in C go sadly wrong if
> you call a nested function indirectly when it has gone out of scope.
> 
> 


-- 
Digby R. S. Tarvin                                              digbyt@acm.org
http://www.cthulhu.dircon.co.uk