RE: [Xen-devel] [PATCH] Xen: fix various checks of unsigned integers < 0

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> diff -r 3cc0fac4a49e -r 52ce5ef855cf
> xen/arch/x86/x86_emulate/x86_emulate.c
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c  Fri Oct 29 14:57:50
> 2010 +0100
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c  Fri Oct 29 14:57:54
> 2010 +0100
> @@ -2102,7 +2102,7 @@ x86_emulate(
>              _regs.edx = (uint32_t)(((int32_t)_regs.eax < 0) ? -1 : 0);
>              break;
>          case 8:
> -            _regs.edx = (_regs.eax < 0) ? -1 : 0;
> +            _regs.edx = ((int64_t)_regs.eax < 0) ? -1 : 0;
>              break;
>          }
>          break;

(/me goes and looks up the cwd instruction...)

Wow, I wonder how many times this code has executed
and returned the wrong (incorrectly sign-extended) value?
Talk about a possible silent-but-deadly bug that would
be impossible to track down!

Nice catch!  Future Xen support people thank you!

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