[FFmpeg-cvslog] r17543 - trunk/libavcodec/x86/cpuid.c

[Reimar Döffinger]

On Tue, Feb 24, 2009 at 11:18:48AM +0800, Zuxy Meng wrote:
> Long mode support itself is reported thru CPUID, and an AMD64 kernel won't 
> ever boot if it can't detect the existence of CPUID.

However AFAICT CPUID is not necessary to detect long mode availability,
the kernel could do the steps necessary to transition to long mode and
see if the LMA (long mode active) bit is set. Failing safe would
probably be hard to do though.
You need to use the RDMSR and WRMSR instructions for that though, and
determining support for them without CPUID would be quite a mess, too.
Well, it does not matter much, when every operating system in existence
would need to be changed also having to change FFmpeg would not be much
additional effort, I was just hoping that you might have something
authoritative.