From: buers AT gmx DOT de (Dieter Buerssner)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Inline ASM
Date: 24 Mar 2000 21:29:54 GMT
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Alexei A. Frounze wrote:

>Yes, I tried. I have *really* working program.

I believe you.
You might have been lucky, your example is wrong. Adding the following
lines at the top of your example to make it compilable.

/* just guesses */
extern unsigned short VGA_sel;
extern char *VGAAddr; /* unsigned char would be preferable */
extern long scanline_width;

#define y2addr(y) ((y)*scanline_width)

and compile it with gcc -O -S, I get the following output:
[Comments are mine again]

        .file   "a.c"
gcc2_compiled.:
___gnu_compiled_c:
.text
        .p2align 2
.globl _putpixel
_putpixel:
        pushl %ebp
        movl %esp,%ebp
        pushl %ebx
        ; there should be a push %edi here
        movl 8(%ebp),%ebx      ;ebx=x
        movl 12(%ebp),%edx     ;edx=y
        movl 16(%ebp),%ecx     ;cl=color
        movb %cl,%al           ;al=color
        cmpl $0,_VGAAddr
        je L3
        imull _scanline_width,%edx
        movl _VGAAddr,%eax
        addl %ebx,%eax
        movb %cl,(%edx,%eax)
        jmp L4
        .p2align 4,,7
L3:
/APP

      pushw   %es
      movw    _VGA_sel, %ax      ;overwrite al!
      movw    %ax, %es
      movl    %edx, %edi
      shl     $6, %edi
      movl    %edi, %eax
      shl     $2, %eax
      addl    %eax, %edi
      addl    %ebx, %edi
      movb    %al, %al           ;Huh, gcc thinks al is still color
      stosb
      popw    %es
/NO_APP
L4:
        ;There should be a popl %edi here
        popl %ebx
        movl %ebp,%esp
        popl %ebp
        ret

I suggest to read (or reread) in the gcc manual about inline assembly.

-- Regards, Dieter