NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/sys/amiga/programmer/5259

Internet Message Format | 1996-08-05 | 3.5 KB

Path: vb.franken.de!volker
From: [e-mail] (Volker Barthelmann)
Subject: Re: 680X0 -> PPC translator?
Newsgroups: comp.sys.amiga.programmer
References: <[e-mail]> <[e-mail]> <[e-mail]>
X-Newsreader: TIN [AMIGA 1.3 950726BETA PL0]
Message-ID: <[e-mail]>
Date: 11 Mar 96 23:02:07 MET
Organization: home


In article <[e-mail]> you wrote:
:
: Well, even so it still doesn't affect the translation process and that's simply becuase in
: order to make a dynamic call (ie run-time address calc.) the base address of the function is
: referenced somewhere in the program right?!

It doesn't have to be.

: so you can collect all these addresses and then see
: where they're used as jump/call operands in an indirect call somewhere else in the program.

Easy said, but really doing this is a different story. First, You'll have to
kind of disassemble the program and therefore You have to know what is data
and what is code, but that's what You want to decide, so...

Also doing this kind of analysis is pretty much impossible on Assembler code.

: remember that all such addresses are 'lea'ed somewhere in the program and probably stored in
: some variable in memory and when needed is used to load an address register for making the jump

And a variable in memory in assembler looks like xyz(a7), but only at one
point, because at another point it is xyz+c(a7). It is probably impossible
to detect if they point to the same address.

: or simply used directly, in either case to resolve the problem of dynamic address resolution,
: address context analysis must be performed on EACH such address in the program, while it
: implies hugh data structures, it is very much theoratically possible. also bear in mind that

It is not theoretically possible. There are some simple cases where it may
work, that's all.

: all external references are assumed to be translated code already, so we don't care about that
: but ALL internal references can be resolved because SOMEWHERE, SOMEONE must have used them and
: don't tell me that function addresses are being used in arithmatic calculations, that is simply
: weird programming, don't you agree and so the exact entry point is located somewhere in the

I don't agree.
Function addresses are often used in arithmetic calculations. Examples are
copying of code or control-structures like in special switch-statements.

: program, hey no one said that the translator has to be a stupid one, hell no, it is pretty much
: intelligent in that respect, that is one of the fields in which it excels i think, to be able
: to resolve dynamic addresses. if the branch is to some externally allocated memory, in which
: case you don't have an address, then this falls under the heading of self

There are many many cases where You don't know the address. You could get the
adress by an external function or it could be contained in data structure etc.etc.

: modifying/relocating code and then you have to simply change the source bytes, meaning the
: code bytes being copied to PPC code ofcourse, however a problem arises if the code size differs
: from the translated code size, then you'll have to locate the code that does the copying and

And You have to locate the place where the memory for the code is allocated
and then adjust it according to the new size for the PPC code. And You have to
change all the other points where this size is used e.g in a loop.
There is absolutely no way to do this reliably.


Volker