Re: [PATCH v3 1/2] ntdll: Add emulation for UMIP instructions.

[Alexandre Julliard]

Brendan Shanks  writes:
> +extern int have_cpuid (void );
> -
>
> +extern void do_cpuid_cx( unsigned int ax, unsigned int cx, unsigned int *p );
> +__ASM_GLOBAL_FUNC( do_cpuid_cx,
> -
>               "pushl %esi\n\t"
> -
>               "pushl %ebx\n\t"
> -
>               "movl 12(%esp),%eax\n\t"
> -
>               "movl 16(%esp),%ecx\n\t"
> -
>               "movl 20(%esp),%esi\n\t"
> -
>               "cpuid\n\t"
> -
>               "movl %eax,(%esi)\n\t"
> -
>               "movl %ebx,4(%esi)\n\t"
> -
>               "movl %ecx,8(%esi)\n\t"
> -
>               "movl %edx,12(%esi)\n\t"
> -
>               "popl %ebx\n\t"
> -
>               "popl %esi\n\t"
> -
>               "ret" )
> -
>
> +static int umip_enabled( void )
> +{
> - /* Check cpuid to see if UMIP is supported.
> -
> * UMIP bit is EAX=0x07,ECX=0x0, ECX bit 2
> -
> * (CPUID.07H.0H:ECX:UMIP[bit 2] in Intel syntax)
> -
> *
> -
> * It would be preferable to check if UMIP is actually enabled
> -
> * (CR4.UMIP), but that can't be done from userspace.
> -
> */
> - unsigned int regs[4];
> -
> - if (!have_cpuid()) return 0;
> -
> - do_cpuid_cx( 0x00000000, 0, regs );  /* get standard cpuid level and vendor name */
> - if (regs[0] >= 0x00000007)   /* Check for supported cpuid version */
> - {
> -
>    do_cpuid_cx( 0x00000007, 0, regs );
> -
>    if (regs[2] & (1 << 2))
> -
>        return 1;
> - }
> -
> - return 0;
>
> +}
> +#endif

There shouldn't be any reason to check this. If UMIP is not enabled you
won't get a fault in the first place.

Also I don't see why you use #ifdef linux, surely that code could work
on other platforms too.