.:: Bots United ::. - gcc function order

.:: Bots United ::. (http://forums.bots-united.com/index.php)

- General Programming (http://forums.bots-united.com/forumdisplay.php?f=25)

- - gcc function order (http://forums.bots-united.com/showthread.php?t=4707)

gcc function order

Is there a way to make sure a function is the first one to be compiled and first one written to the executable/object?
Since I'm not using any libraries passing -nostdlib to gcc will require _start instead of main.
This works fine except if _start is not the first function the whole thing messes up.
What happens is...
Compile->Link->copy code to raw binary

I did try a hack where I put a function at the beginning of the source file which called _start but after adding a few more functions that broke too.
My goal is the smallest possible binary size, which is why I'm working directly with hardware instead of using a high level library...

Code:

#include <gba_base.h>

#include <gba_video.h>



#define FRAMEBUFFER ( ( volatile u16* ) 0x06000000 )

#define RGB15( r, g, b ) ( ( r << 10 ) + ( g << 5 ) + ( b ) )

#define ru32 register u32

#define ru16 register u16



// HACKHACKHACK

// MAKE SURE THIS IS THE FIRST FUNCTION IN THE ONLY SOURCE FILE

void _start( void );

static void GCCStartHack( void ) {

        _start( );

}



// Draws a 1 pixel wide line at the given coordinates with the given height

static void line( ru32 iX, ru32 iY, ru32 iHeight, ru16 iColor ) {

        ru32 iTarget = iY + iHeight;



        for ( ; iY < iTarget; iY++ )

                FRAMEBUFFER[ iX + ( iY * 240 ) ] = iColor;

}



static void game_drawborder( void ) {

        line( 70, 10, 150, RGB15( 15, 15, 15 ) );

        line( 170, 10, 150, RGB15( 15, 15, 15 ) );

}



// DO NOT ADD ANY CODE BEFORE THIS FUNCTION

void _start( void ) {

        REG_DISPCNT = MODE_3 | BG2_ENABLE;        // Set framebuffer mode



        game_drawborder( );



// Enter infinite loop 

main_loop:

        goto main_loop;

}

I haven't gotten far but that compiles to around 60 bytes, it'd be smaller but for some reason thumb code isn't working.
Here is my cheap makefile...

Code:

CC=arm-elf-gcc

OBJCOPY=arm-elf-objcopy

CFLAGS=-Os -fomit-frame-pointer -mcpu=arm7tdmi -I/home/lazy/dev/tools/devkitARM/libgba/include -c

LFLAGS=-mno-fpu -nostdlib



minitris.o:

        $(CC) $(CFLAGS) -o minitris.o minitris.c



minitris.elf: minitris.o

        $(CC) $(LFLAGS) -o minitris.elf minitris.o



minitris.gba: minitris.elf

        $(OBJCOPY) -O binary minitris.elf minitris.gba



all: clean minitris.gba



clean:

        rm -fv *.o

        rm -fv *.elf

        rm -fv *.gba

Any help is appreciated since I'm new to gcc and this won't work unless _start is at the beginning of the binary.

Re: gcc function order

not sure if a custom link script (like that one in Metamod-p) will work, but I have never done this so I don't know further.

Re: gcc function order

ouch, w/o any libc you will be very much on you own, no one does this for long :)

Prehaps give dietclib a try, it's commonly used in embedded and mirco linux systems (4 mb ram+).

--OK

Re: gcc function order

Actually, the only ram I have to work with is 256kb - and even that is cut down since in my case it is shared with the program itself.
http://en.wikipedia.org/wiki/Gba

I just want to see if I can code a simple game in less than 256 bytes. I know it has been done for x86 but I wanted to see if it's possible with C since all of the ones I looked at were done in assembly.

But it's not going anywhere since gcc seems to put _start wherever it wants which results in some other function getting called and the system not being initialized.

I'm going to try a few more things later tonight and see what happens.

Re: gcc function order

well, then good luck :)

Re: gcc function order

You should ask the guys at the demo scene (start at www.pouet.net if they have a forum there). They know how to do heaps of things in 256 bytes.

Re: gcc function order

Bah.
Got too frustrated with it so I decided to port sdl sopwith to the nintendo ds.
Its working very well on real hardware so once I get the input and sound finished I can release it into the wild.
:)