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Date: Sat, 12 Aug 2000 21:40:00 +1000 (EST)
From: Iain Templeton <iain@research.canon.com.au>
To: andrew@ugh.net.au
Cc: freebsd-hackers@freebsd.org
Subject: Re: libvgl: free(): warning: junk pointer, too high to make sense.
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On Sat, 12 Aug 2000 andrew@ugh.net.au wrote:

> Hi,
> 
Hi Andrew :-)

> I'm using libvgl but when I call VGLTextSetFontFile(FONT) I get:
> 
> free(): warning: junk pointer, too high to make sense.
> 
> What am I doing wrong? The only other vgl call I have made at this point
> is VGLInit.
> 
Well, VGLInit() calls VGLTextSetFontFile((byte *)0)

We see in VGLTextSetFontFile() that

  if (filename==NULL) {
    VGLTextFont->Width = 8;
    VGLTextFont->Height = 8;
    VGLTextFont->BitmapArray = VGLFont;
  }

But I think that when you call VGLTextSetFontFile() later you'll run the
code at the beginning of the function

  if (VGLTextFont) {
    if (VGLTextFont->BitmapArray) 
      free (VGLTextFont->BitmapArray);		<--- This Line
    free(VGLTextFont);
  }

So what I suspect might be happening is that its the free() of the line
marked above thats failing, because it is trying to free something at
the address of VGLFont, which is a global array within libvgl.a.

Using gdb on the program should make it possible to confirm that or not.
As for how to get around it, I would say that this is a bug in libvgl.

> Also what sort of file is it after? I guessed one of the fonts in
> /usr/share/syscons/fonts/ after uudecoding...
> 

I think it might be. It reads the first 2 characters as width and
height, then the rest seems to be raw font data, which is read into
memory, not sure of the format other than that though.

Iain



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