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Mail Archives: djgpp/2000/05/06/13:48:50

From: buers AT gmx DOT de (Dieter Buerssner)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: inline asm problem
Date: 6 May 2000 18:06:54 GMT
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Paul Crone wrote:

>Please help.  I've used the following inline assembly code function in
>my program using gpp 2.8.1 and all was well.  I've just made a new
>installation on a different PC using gpp 2.9.5.2 and get a compiler
>error.  What have I missed?

There is a change in the handling of inline assembly in recent
versions of gcc. You are not allowed anymore, to put registers
in the input-list into the clobber list

>inline void set_vesa_bank_pm(int bank_number)
>{
>   asm (
>   " call *%0 "
>    :                             /* no outputs */
>    : "r" (pm_bank_switcher),     /* function pointer in any register */
>   "b" (0),                    /* set %ebx to zero */
>   "d" (bank_number)           /* bank number in %edx */
>
>    : "%eax",                     /* clobber list (we have no way of */
>   "%ebx",                     /* knowing which registers the VESA */
>   "%ecx",                     /* code is going to change, so we */
>   "%edx",                     /* have to assume the worst and list */
>   "%esi",                     /* them all here) */
>   "%edi"
>   );
>}

On possible (untested) fix, is to use temporary vars like:

/* Assume, the VESA-function does not change ebp */
  int unused1, unused2, unused3;
  asm (" call *%5 "
       : "=b" (unused1), "=d" (unused2), "=a" (unused3)
       : "0" (0), "1" (bank_number), "2" (pm_bank_switcher) 
       : "ecx", "esi", "edi" /* all other registers */); 

Or you push all the registers yourself onto the stack, call the function,
and pop the registers again.

  /* Untested */
  asm ("pushal; call *%2; popal"
       : 
       : "b" (0), "d" (bank_number), "r" (pm_bank_switcher));

-- 
Dieter Buerssner

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