Message-Id: <3.0.6.32.20000413223445.007be930@pop.crosswinds.net>
X-Sender: shinelight AT pop DOT crosswinds DOT net
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Date: Thu, 13 Apr 2000 22:34:45 -0500
To: djgpp AT delorie DOT com
From: "Thomas J. Hruska" <shinelight AT crosswinds DOT net>
Subject: Help with Inline ASM...
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Reply-To: djgpp AT delorie DOT com

Hello, I got the following code to work (new to AT&T ASM, somewhat familiar
with Intel):

#include <stdio.h>
#include <conio.h>

int main(void)
{
  int x, y = 32;

  x = 0;
  x++;
  printf("%i\n", x);
  // Form __asm__ __volatile__ ("Code" : outputs : inputs :
registers-modified);
  // Allowed to destroy eax, ecx, edx, fs, gs, and eflags (although
pushing/popping them
  // is a whole lot safer
  __asm__ __volatile__("
      push %%eax
      movl %0, %%eax
      rol $32, %%eax
      movl %%eax, %0
      pop %%eax"
      :
      : "g" (x), "g" (y)
      : "ax", "cx", "memory"
      );
  printf("%i\n", x);
}

Basically, the ASM code does nothing, but I want to be able to self-modify
the code during run-time and replace the number $32 with the value in y.
The assembler complains whenever I try replacing the $32 with a variable
and I think that the only way that I am going to get that number to change
is to self-modify.  If someone knows of a better solution, let me know.
Otherwise, how do I self-modify ASM code in 32-bit PM (if such a thing is
even allowed).

Thanks in advance!


           Thomas J. Hruska -- shinelight AT crosswinds DOT net
Shining Light Productions -- "Meeting the needs of fellow programmers"
                  http://www.shininglightpro.com/