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Date: Thu, 06 May 2010 06:37:00 -0000
Subject: [Bug inline-asm/43998]  New: inline assembler: can't set clobbering for input register
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mmarkk@mmarkk-desktop:~/src/vmdetect$ gcc --version
gcc (Ubuntu 4.4.1-4ubuntu9) 4.4.1
----------------------------------------------
#include <sys/types.h> 
#include <stdio.h> 
int main (void)
{
  size_t ecx;
  asm ("cpuid": "=c" (ecx): "a" (0x1):"eax","ebx","edx");
  printf ("Suspected %s machine!\n", (ecx >> 31) ? "virtual" : "real");
  return 0;
}

mmarkk@mmarkk-desktop:~/src/vmdetect$ gcc 1main.c 
1main.c: In function ‘main’:
1main.c:7: error: can't find a register in class ‘AREG’ while reloading ‘asm’
1main.c:7: error: ‘asm’ operand has impossible constraints
------------------------------------------------
#include <sys/types.h> 
#include <stdio.h> 
int main (void)
{
  size_t ecx, dontneed;
  asm ("cpuid": "=c" (ecx),"=a"(dontneed): "a" (0x1):"ebx","edx");
  printf ("Suspected %s machine!\n", (ecx >> 31) ? "virtual" : "real");
  return 0;
}
works OK.

How to correctly say compiler about clobbering eax register ?


-- 
           Summary: inline assembler: can't set clobbering for input
                    register
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: inline-asm
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: socketpair at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43998