From:	"lewi9908" <lewi9908 AT ghc DOT ctc DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	AT&T inline asm in DJGPP...
Date:	Sat, 30 Nov 2002 08:50:31 -0800
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

I am tring to build an OS...

I have a bootsector that loads a loader that setup PMode and loads the DJGPP
built program(not yet a real OS kernel)...

Using the next code

CStartup.asm (NASM)

[BITS 32]

extern _main
call _main
retf

Ker.cpp (DJGPP)

int main()
{
    char* screen = (char*)0xb8000;
    const char* msg = "Hello, world!";

    while (*msg)
    {
       *screen++ = *msg++;
       *screen++ = 0x4f;
    }

    return 0;
}

This allows me to make a far call to FLAT_CCODE:0x0000 which FLAT_CCODE is
the PMode gdt based at 0x20000 When main() return the CStartup.asm use retf
to return to loader...

Now before moving to DJGPP I was using Borland C++ 3.1 which is 16-bit so
main() had to loop for forever and not end the function and it used asm to
print to print to screen...

void main()
{
 char* pC = "Hello World";

  asm {
   mov si, word ptr pC
   cld
  }
 PrintAgain:
  asm {
   lodsb
   or  al,al
   jz  short PrintOver

   mov ah,0Eh
   mov bl,4fh
   int 10h

   jmp short PrintAgain
  }
 PrintOver:
 for(;;);
}

Note: there was some rule that inline asm couldn't have labels so C labels
are used and the asm is broken up in to two...

Now I have looked into AT&T inline asm in serveral online docs and haven't
found a real good source of infomation and examples...

Also I was thinking about just using NASM to make to asm code to link with
the C code and setup gobal/extern to make funtion call to the asm from C.
But I don't know if this is best but looking at Mixed ASM/C it look easier
to do...

That is all I have...

Any more help...

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