From: broeker AT acp3bf DOT knirsch DOT de (Hans-Bernhard Broeker)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Problems with DJGPP lib and grx23
Date: 29 Nov 1999 15:50:19 +0100
Organization: RWTH Aachen, III. physikalisches Institut B
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References: <4 DOT 2 DOT 0 DOT 58 DOT 19991126181032 DOT 00a65c40 AT hal DOT nt DOT tuwien DOT ac DOT at>
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Anton Helm (tony AT dictator DOT nt DOT tuwien DOT ac DOT at) wrote:
> At 07:40 PM 11/24/99 +0100, you wrote:

> Well, if you know what you are looking for, you probably find it. I
> don't.  Program crashes at _GR_shift_scanline+99 while running the
> first inline asm part.  This is somewhat mysterious as 99 is
> definitely out of this inline asm part.  (See the second asm file
> attached below.)  

No, it isn't. That '99' is decimal, I think, i.e. it's the code found
at address 0x63 in the disassembled listing, and that code is

	movb (%ecx),%ah

and comes from the inline asm part of the routine. To quote the 2.81
disassembly:

   56:  8a 2e           movb   (%esi),%ch
   58:  eb 06           jmp    60 <__GR_shift_scanline+60>
   5a:  8d b6 00 00 00  leal   0x0(%esi),%esi
   5f:  00 
   60:  4e              decl   %esi
   61:  88 e8           movb   %ch,%al
   63:  8a 26           movb   (%esi),%ah
   65:  88 e5           movb   %ah,%ch

That's the beginning of the inline assembly block. As you see, %esi was
chosen for term '%3' of the inline assembly. Same part, in 2.95 asm:

   51:  8a 29           movb   (%ecx),%ch
   53:  eb 0b           jmp    60 <L7+3f>
   55:  8d 74 26 00     leal   0x0(%esi,1),%esi
   59:  8d bc 27 00 00  leal   0x0(%edi,1),%edi
   5e:  00 00 
   60:  49              decl   %ecx
   61:  88 e8           movb   %ch,%al
   63:  8a 21           movb   (%ecx),%ah
   65:  88 e5           movb   %ah,%ch

I.e., it chose %ecx for %3. But that's *wrong*. It shouldn't have done
that, as %ch which is explicitly used is part of %ecx, and thus %ecx
is not available for holding an input/output expression.

So it looks like putting '%ch' into the output register list of that asm
block was not enough. Whole %ecx will have to be put there... I don't
know the exact syntax, though...

It's really time for the grx23 code to be patched, accordingly, or at
least an 'official' patch should be made available, by its
maintainers, on their web site.
-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.