Re: [dpdk-dev] [PATCH v3] eal_common_cpuflags: Fix %rbx corruption, and simplify the code

[Neil Horman <nhorman@tuxdriver.com>]

On Mon, Mar 24, 2014 at 01:47:55PM -0700, H. Peter Anvin wrote:
> On 03/24/2014 12:52 PM, Neil Horman wrote:
> >>
> > To add an extra sanity check in rte_get_flag_enabled.  If we were moving to the
> > use of C99 initalizers, I wanted something to catch the possibility that we skip
> > a flag by accident (i.e. leave a zero initalized hole in the array).  Except 0
> > from my read is a valid value for all the fields of the array.  So I bumped up
> > the cpuid register enum by one and wrapped it in a macro.  That way we can test
> > for !feat->reg as an indicator that we're requesting feature support for a flag
> > thats not listed in the array.
> 
> It actually isn't: there aren't any flags in CPUID leaf 0, so since the
> code only looks for bits it'd be perfectly okay to reject leaf 0.
> 
> Another thing that I noted is that the code doesn't actually check that
> any particular leaf is valid (by checking the maximum leaf number in
> CPUID leaf 0xXXXX0000:EAX).  Especially for the leaf 7 features this
> could result in false positives, which obviously would be disastrous.
> 
Thanks, I'll improve this checking today.

> 	-hpa
> 
> 
>