Odd programming question

[trekiej]

Outside of header files and libraries, when does OS specific information get added?
When I run a programm, how does  the OS allocate memory and give control to the application and the application give it back.
The OS gives the application access to resources, how does it know what to give?
Source > Object > linking > Binary

[Piru]

@trekiej

Outside of header files and libraries, when does OS specific information get added?

Could you clarify that question a bit? What OS specific information?

When I run a programm, how does the OS allocate memory and give control to the application and the application give it back.

OS allocates memory in whatever way it does. You don't need to worry about that. Or what exactly are you asking here?

Entering the application typically happens by entering the very beginning of the first (code) segment. Application gives the control back by executing 'return from subroutine' with the original stack pointer (some platforms have different way to terminate, however).

The OS gives the application access to resources, how does it know what to give?

Again, I'm not quite sure what you're asking here. Access control for privileged resources?

[Trev]

In Amigaland, you transfer control to the operating system by calling library functions. Piru knows a lot more about this than I do, but generally, your header files include function table offsets (indexes). You store the library base address in your application via LoadLibrary, and a call to a function loads the table and jumps to the address referenced by the index.

In other systems, control is usually passed to the operating system using a system call instructon or interrupt or an invalid instruction exception trapped by an operating system dispatch routine. Windows uses INT 2E, for example, and Linux uses INT 80 (on x86--different architectures provide different means for making system calls).

For resources, the system functions store and keep track of allocations. For example, AllocMem and AllocVec track memory allocation. It's the application's responsibility to notify the system when those resources are no longer needed. This is true in most operating environments, althogh some, like Java, have garbage collection routines that will clean up resources that are no longer in use.

[trekiej]

Thanks alot.  I want to know more about OS and Application interactivity.

I guess I need to find out how a kernel works to get the info. in need.  As CSI Grissom would say, I am looking for the right question.

I know I have asked a similar question before and it led to System Calls.  I want to know how my application gets to the real world and there seems to be more than one answer.

What I wish I could do is learn how to use the header files and libraries to make a window to put my app.
Right now making a console app on an Amiga will do.
I wish they would teach Amiga Dos in college.

Windoz,Windoz,Windoz  :-(

[Piru]

Well, considering this is in Alternative Operating Systems section I don't think he's asking about AmigaOS ABI in particular.

[Piru]

Erm. Now I'm really confused.

If you're writing programs you don't need to know how the ABI works internally, It Just Works.

If you wish to have a GUI, look into intuition and gadtools, or if you wish to have something more fancy, MUI. All of those have plenty of programming examples (intui in RKRM, MUI in mui dev archive).

[Kronos]

If you just want to use Amiga-Windows ...

[shameless plug]
http://www.steamdraw.de/intuition1.c
http://www.steamdraw.de/intuition2.c
http://www.steamdraw.de/intuition3.c
http://www.steamdraw.de/intuition4.c
[/shameless plug]

 :-D

[Piru]

And while we're at it:

http://www.iki.fi/sintonen/src/misc/simplewindow.c

[trekiej]

I feel like there is information added during compile time that the user does not have to provide.

[Piru]

Such as?

(There is startup code added normally, but why would you need to worry about it?)

[trekiej]

@ Piru:
Maybe that is what gets me.   :-D
Learning C in an intro class we used include iostream.h to get I/O.
How does iostream.h work?

[Piru]

That's C++.

Why would you need to worry about how it works? Those things are something you don't need to worry about. You can concentrate on your own code.

Anyhoo, iostream is typically compiler specific. If you really must, you could take a look at gcc implementation for example. I can't see a reason to bother oneself about such messy details, however.

[trekiej]

Alright, thanks.
I will put this on the back burner.
I will look into how to work with libraries, etc.
I can not seem to get my c++ finished.  I guess I can still work with the Amiga without it.

[Trev]

There's nothing wrong with wanting to know how it all works, but what I think Piru is getting at is that you don't need to know how system calls work to write userland applications. All you need is a set of standard C (or C++) libraries, and you're good to go, on just about any operating system.

The source code for most C runtimes is available from the runtime's publisher. Even Microsoft ships runtime source code with their commercial compilers. Unfortunately, Amiga compilers are the exception, unless you're using gcc. Mapping most C library functions to an Amiga library function isn't too difficult, though.

MIT's OpenCourseWare program has a nice operating systems class available at http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-828Fall-2006/CourseHome/index.htm You'll start out by looking at how UNIX works, and by the end of the class, you'll have written your own operating system.

[Piru]

Sure all that is very interesting indeed, but I think it might be a bit too early for trekiej to delve into all that yet.

Granted, class explaining how to build your own OS from scratch could work even for beginners (as you then are not required to read and understand thousands of lines of existing code).