Hi,

Tony Wyatt wrote:

What about some advice on coding habits?

Bah, I'm not a teacher :) And I don't have any skill sin teaching whatsoever... I can't even explain very well...

Much old 68k code is fast and efficient because it relies on parameters like library and structure pointers remaining persistent in allocated 68k registers, eg a2, a6 always point to particular structures. In a big module consisting of dozens if not hundreds of very small functions, only one or two registers are ever used for volatile data. Most parameters are passed in assumed registers, so loading of arguments is minimised.

Uh, I beg to differ. I think he old habbit of keeping certain registers set up with a default meaning is the worst you can do, /especially/ when you have so little registers as the 68k. You say loading of arguments is minimised, but that's wrong.

The effect is two-fold:

1. Since some registers are fixed, this results in lots of splilling of scratch registers. A lot of code is "just" about moving stuff from memory into registers, manipulating it, and storing it back. Sure, the 68k can do a lot of it's operations also in memory, but that's much slower. The result is that with fixed registers like this, theamount of availabele registers is decreased. 2. Fixing registers will make them hang around forever, even when they aren't used. What use is it to have a2 and a6 constantly setup when there's no need for them at the moment, and they could be reused for other stuff ?

Modern compilers make "lifeliness analysis" (sp?): They assume "virtual" registers, analyse their life cycle, and assign them to hardware registers. This is nearly optimal in modern compilers, and far bettern than you would do it in your hand-written assembly code.

So what is a good way to maintain this register shortcut in a C version of a big program originally written in assembler? Obviously I can specify parameters to be passed in 68k registers, but I am trying to write this thing in a portable fashion, machine-independent.

There's not really any way to enforce this in C on the PPC. You can not assign a register to a variable, for example, and as I explained above, I wouldn't do that. One of the things to remember about the PPC is that it is a pure load/store architecture: You can not, like on the 68k, manipulate data in memory. It _must_ be in registers to be processed. The compiler will do this optimally, it will also try to keep variables in registers where appropriate, based on it's analysis.

I have no experience with PPC code yet. Is there a way to ask gcc to use registers for certain parameters, in a platform-independent way? I want the C code to remain pure ANSI-compliant. It would be nice to leave the code unchanged from its present SAS/C environment to PPC and gcc.

ANSI-compliant and specifying registers doesn't really mix ;)

There's no way to specify the placement of parameters on OS4. It's fully System V.4 compliant.

System V.4 places integer and pointer parameters into r3 - r10, and floating point parameters into f1 - f10. Excess parameters (which doesn't happen that often) are put on the stack. The only exception to this in OS4 is the VARARGS68K attribute, which places all parameters on the stack, to cope with 68k compatibility.

BTW, Linux PPC also uses the System V.4 ABI, so if for example Kaffee already contains trampoline code for Linux PPC, you can re-use that, it won't be different in OS4.

So bottom line, the best way to do it on OS4 is not to specify the placement, and everything should fall into place. Plus, the compiler will definitely know better how to use registers.

Regards,

Hi,

Timothy Cameron wrote:

Excuse the dumb question, but why use the stack for "Excess parameters" when the PPC has 32 general purpose and 32 floating point registers?

The other registers (r14 +) are "non-volatile", i.e. they must be preserved across function calls. The compilers uses them for local variables. r0, r3-r10, r11, r12 are volatile, i.e. they need not be preserved (with r3-r10 used as parameters when a function is called). Similar rules are in place for the floating point registers.

Please note the last time I've done any 68K ASM was on the "Sinclair QL" many years ago. I have not looked at PPC ASM yet either.

Is this "System V.4" limitation something to do with GCC?

Well, it's one possible ABI gcc supports (besides PowerOpen, AIX and WindowsNT).

However, it's not really a limitation, but a set of rules. It makes things a lot easier, since parameters are now defined by the C prototype of a function, and no compiler specific bindings for parameter passing is necessary... On the old system, every compiler had it's own rules: Aztec C used to pass parameters on the stack, SAS/C could select stack or register arguments, gcc used stack, etc.

Regards,

Hi,

Rose Humphrey wrote:

...

To dispell the silence a bit (hehe, any D&D fans here ;),

You called?

I knew you would say that ;)

...

Are there any projects up for grabs that I can look into ?

You are a very foolish perso, posting things like this.

No, just brave enough ;)

Actually, if someone could find it in him to write a Guide to Porting *nix Apps to OS4, even just a rough one that could be tidied up later, and/or by others, it would be a useful start.

Argh... I would love to do something like that, but my writing skills suck, and I can not really explain anything in a way people understand... sorry...

And if it were coupled with a How To Compile Using GCC for AmigaUsers, we might even be able to draw in a few extra coders...

You touch a sore point there, I have to admit. Documentation is really missing right now, but we are lacking the resources to do that properly... The only thing we can offer is to answer questons when people ask them...

Regards,

Le 02/05/2005, Thomas Frieden a écrit :

...

And if it were coupled with a How To Compile Using GCC for AmigaUsers, we might even be able to draw in a few extra coders...

You touch a sore point there, I have to admit. Documentation is really missing right now, but we are lacking the resources to do that properly... The only thing we can offer is to answer questons when people ask them...

I suppose if someone, even a total idiot (as far as programming is concerned) like me collected all the hints and tips it might help?

Maybe a Wiki format, although I'm not too happy with the "anyone can write/modify/delete" ethos. I'll need to look at this.

Salutations

Le 03/05/2005, Thomas Frieden a écrit :

Hi,

Rose Humphrey wrote:

...

I suppose if someone, even a total idiot (as far as programming is concerned) like me collected all the hints and tips it might help?

Theoretically, if you understood what I said... I normally don't understand it when I re-read it :S

Sounds like a perfect demonstration of the Second Law of Thermodynamics using knowledge instead of energy.

Salutations

Hi,

Peter Bengtsson wrote:

...

Argh... I would love to do something like that, but my writing skills suck, and I can not really explain anything in a way people understand... sorry...

If it would help, I could attempt to aid you in writing such a document (or write it with your input and corrections). Not that I have a lot of time, but I do work as a teacher (ComputerScience/SystemsProgramming) and even if I am not great at writing I have a little bit of practice.

Thanks for the offer, but as I said, my skills at explaining are rotten...

So, if you feel up to it I can probably come up with a (very) rough outline of such a document during the weekend (or possibly earlier) and we can take it from there. (If you say yes, you should also know that I write everything in LaTeX)

Whoa, LaTeX, the word processor's assembly language :) Used that during my university days, but that's long past ...

Regards,

On 30/052005, you wrote:

Hi,

Sorry, late, I know...

Mark Bond wrote:

...

The automake and autoconf scripts need testing now we have perl,

Are these already available for download ? I looked at the site, and couldn't find them.

Regards,

Thomas,

All the details are on the project site, but from what I can remember, the investigator said teh scripts are all just perl scripts (and so should just need testing), although I highly suspect a unix type shell will be needed, from the testing of perl that I've done generally.

Mark

Hello Olly,

On 03/052005, you wrote:

Thomas Frieden wrote:

...

Are there any projects up for grabs that I can look into ?

Slightly worrying is that our fearless leader hasn't stepped up with something for you to do :)

Our fearless leader, has two assistants (one of whom is myself), in his prolonged abscence (no I have no idea where he is), I did reply with a couple of tasks for Thomas.

What were the dependencies and which ones have already been taken?

Regards

Mark