Re: [PATCH] x86: Don't use NOPL on 32-bit cpu's because not all systems support it.

David Sanders
2008-09-16T17:48:37Z

On Tuesday 16 September 2008 12:32, H. Peter Anvin wrote:
> Oh good grief.
>
> VPC is apparently so broken that these instructions work *some* of the
> time, which may include the first time, but not later.  That is an
> impressive level of cockup.
>
> Given that, we should either just rip this code out, or detect VPC
> (how?).  The latter option can be done post-.27, of course; if so, we
> should just force the bit off for now rather than doing it in the
> alternatives code.  The only reason for doing the latter at all would be
> to mitigate the overhead of paravirt_ops and other dynamic patch sites.
>
> It would also be the least impact for .27, I believe.

I think you still want the nopl enabled for 64-bits.

This is how I detect virtual pc. I based it on a google search. Microsoft
itself provides no info:

#include <stdio.h>
#include <signal.h>
#include <stdlib.h>

void except(int e)
{
printf("Not in Virtual PC\n");
exit(1);
}

int main()
{
signal(SIGILL, except);
asm("\n"
"mov $0x01, %eax\n" /* function number */
".byte 0x0f, 0x3f, 0x07, 0x0b\n" /* call VPC */
);
printf("Inside Virtual PC\n");
return 0;
}